Every year, construction presents developers with not only new materials, but also methods for constructing residential buildings. Of course, such innovations occur much less frequently than the discovery of a new product, but they still occur. For example, not so long ago a fashion came to the CIS countries - a rafter system in the form of a pitched roof. This innovation immediately caused a storm of emotions and indignation among developers. The fact is that for quite a long period two slopes were considered the standard roof, but here there is only one. Let's look at such a system in more detail.
Introduction
Some people think that a pitched roof, by design, can only have a gentle slope, but this is not so. The slope of such roofs can reach 65 degrees. Large values can be explained by the presence of attic space in the building.
This type of roofing is performed both with and without a ventilation system. Its absence is most suitable for open terraces. It is in this case that there is no need to create a steep slope, and often this roof slopes only 5-7% in order to have natural precipitation. Positive feature What can be noted about flat roofs is that, thanks to their design, they allow you to mark out some buildings or adapt the roof area to your needs, for example, you can arrange a swimming pool or lawn. It is worth noting that if you do not plan to burden your roof with additional elements, then it will be enough to create a ventilated type with a slope of 5 to 20 degrees.
In private construction, pitched roofs, as a rule, are used only on outbuildings and very rarely on residential buildings, but over time, more and more developers are choosing the second option, because it is quite profitable. But, as with everything, there are downsides and as for this roof, you may have problems with it winter period of the year. The fact is that a small roof slope will collect quite a large number of snow, therefore, it needs to be cleared off periodically, and if you don’t do this yourself and hire a team of cleaners, you can end up costing a pretty penny.
The rafter system of these roofs is similar to gable roof, but is only part of it.
Shed roof rafters
If you are an experienced roofer, then you probably know what hanging and layered rafter legs are, but for people who are far from construction, I will try to explain it in the most understandable language.
The use of different types of rafters depends on various nuances, for example, the slope of the slope, the width of the building, the span distance or the external shape of the structure. Only by making calculations that take into account all these parameters can you understand the type of future roof.
It is worth noting that the use of hanging rafters was most often seen in buildings whose width is 4-5 meters, and for larger values it is necessary to use additional struts resting on special protrusions. Such elements can be used up to seven meters, but if this is not enough, then vertical stops, called headstocks, and struts that fix these vertical elements are added to this system.
Now let's figure out what such systems actually look like.
Hanging rafter system
Experienced assemblers of roofing systems will unanimously answer you that there is no system more complex than the use of hanging elements in it.
In order to create the necessary roof on your own, you will need not only a clear drawing, but also a complete understanding of your own actions. If you pay attention to the mistakes of many developers, then I advise you to choose the highest quality Mauerlat for a pitched roof. After all, it is on it that the entire weight of the roofing system will converge. This beam is laid along the main walls and is rigidly attached to it using embedded parts or other methods. By the way, for pitched roof you would only need two Mauerlat.
The construction of a pitched roof is very simple and the support beams need to be placed only on the lower and upper walls. In fact, the top element will not be a Mauerlat; rather, it performs the functions ridge beam, but despite this, it should be laid according to all the rules of the Mauerlat. It is worth noting that in places where the wood adjoins the wall, it is necessary to lay several layers of roofing felt as a waterproofing material. This is done so that moisture impregnating the outer walls cannot damage the structure of the wood. After all the processes, the rafter legs are laid on top of the support beam and fastened to it.
This structure will be an independent supporting system with a given slope.
By the way, I promised that I would use clear language, so let's be clear on the following definitions:
- Grandma– a vertical part that performs the function of a stand. The ends of this element are located between the rafter legs and the purlin. This beam, in turn, is located on interfloor covering building
- Strut- a wooden beam located at a certain angle. Its main task is to fix the previous element - the headstock, therefore, it is located there. The brace can be used without holding vertical elements, but in this case it will support the rafter legs and rest on specially created protrusions
- Run. It looks like a reliable and massive wooden beam. Multiple struts and various types of racks rest on this element
Rafter system made of layered rafters
Now that we have understood a little about hanging rafters, we can move on to the next type - layered rafters. Basic distinctive feature of this system is that they rest on the main walls rather than on projections. Collected together, additional elements in the form of struts and racks, resting on the main walls, allow you to move the walls of your house a considerable distance, but if you do not need to build a huge house, then you can be content with a simple system and thereby save on material.
Rough calculations allow developers to take into account all the nuances, so when constructing a building yourself, do them as well.
Let's look at the range of distances and see how the configuration changes rafter system.
- From 7 to 12 meters. This width is the most common option for constructing pitched roofs. In this design there will be only one auxiliary rack (which will be equal to the width of your building), resting against the load-bearing wall. Installation of such a rack is possible only if the structure of the house has a main wall, which will bear the entire mass of this element.
- The case when the width of the house is in the range from 12 to 14 meters. This length is quite a common occurrence, because when residents do not want to huddle in a very small space, they expand it somewhat. According to statistics, a standard house is considered to be a square of 10x10 meters, but these parameters can be changed at will.
This width allows the use of the following type of rafter system. The vertical support is built in such a way that on one side it finds support in a reliable wall, and on the other in the rafter legs. By the way, such roofs, in addition to their design, must include auxiliary struts in order to support the rafters resting on the wall inside the building
- Distance 14-16 meters. It’s a rare occurrence to come across such wide rafter systems, but they still happen. As a rule, these structures are not housing, but rather outbuildings, because with such dimensions of the system, it is difficult to talk about safety or any savings. Wide spans will make it possible to erect a pitched roof on them only if the building has two stable walls. It is on them that the vertical posts and multiple struts will rest. But outbuildings with interior walls are a rather rare sight.
Remember that covering the roof with profiled metal sheets is only possible on roofs with a slope of more than 20 degrees.
The metal analogue - metal tiles must be laid on steeper slopes in order to reduce the load on the wooden elements of the rafter system.
When laying metal roofs do not forget about high-quality waterproofing and vapor barrier of the roofing pie, because this type the coating, although protected by special polymers, will quickly begin to corrode when exposed to excess moisture and you will need to replace damaged sheets with new material.
Installation of a pitched roof rafter system
The scheme according to which the truss system of a pitched roof is erected has two types.
- The installation of rafter legs on support beams laid on load-bearing walls, which in turn are located in different planes. This option is recognized as the most expedient in terms of financial efficiency, because it is with this structure that it is possible to save quite a large number of wooden elements. But you should understand that you won’t be able to save much. The point is that in order to ensure a certain roof slope, it is necessary to set an angle, and this can only be done by erecting a large wall
- Installation of a standard triangular system. It contains the usual rafter legs, beams and posts. Thanks to this design, there is no need to increase the length of the walls, but this consumes much more lumber. Therefore, if you have access to it, then you can safely choose this type, but if the situation is the opposite, then think about the first one. By the way, if you have a crane, such a rafter system can be assembled directly on the ground, and then, using mechanisms, delivered to where it is needed. This trick will significantly save you not only time, but will also be as convenient as possible for installers
IMPORTANT: Choosing one of the above methods for constructing a rafter system will not in any way affect the service life of the roof and will not in any way affect the quality of the structure. Design features– individual preference of the developer.
The number of auxiliary supports or struts will largely depend on the following parameters:
- Roof slope
- Weight of rafter leg
- Rafter lengths
- Roofing
- Characteristics of thermal insulation boards
- The gap between the wall and the roof junction
As a rule, installing rafters for a pitched roof is a very simple job; the main thing is to choose the appropriate material and if you don’t know how to do it, contact a specialist or consult a store salesperson. By the way, fastening the rafters of a pitched roof should be done using large nails or metal staples, but in addition to them, special grooves are cut out on the wooden elements in order to create a strong stop.
Remember that the Mauerlat in the rafter system of a pitched roof is the basis. That is why choose it wisely and wisely.
The shed roof design is most likely the simplest design in construction industry. Thanks to it, you can build inexpensive housing or cover a temporary structure, such as a barn or woodshed.
Due to their design, as a rule, shed roofs are not created with a very large slope, which makes it possible to lay bitumen coatings. Ruberoid will be excellent choice on an outbuilding.
It is worth noting that a pitched roof will look rather meager and primitive if you do not apply architectural tricks to it, for example, covering the building and the garage at once. Of course, such a design will take more money out of you, but you will be very satisfied. If you do not need to set up complex systems, then you can stay with a simple form.
-
Rafter system of a pitched roof In terms of the level of assembly complexity, it is one of the simplest options, and also the most economical in terms of material consumption. Therefore, this design is most often used for roofing utility rooms: garages, outbuildings, workshops and others. But also this type rafter frame also used for residential buildings.
However, despite the ease of assembly, in the design of pitched roofs, and even more so during their construction, it is imperative to comply with all the rules and requirements in accordance with SNiP. Why do you need to take the assembly of such a simple rafter system seriously, and what should you consider during the work process?
What are the advantages of pitched roof types?
As mentioned in the introduction, a shed roof is superior to gable roofs in terms of ease of construction. Such a roof can be erected even alone, and in a shorter time. In addition, there are many other positive aspects that make it worth choosing this option.
1Significantly lower material consumption:
2 Easy to install. All the work can be done by one person, because there is no need to assemble rafter pairs, and even more so to lift heavy parts to the place where the rafter frame is assembled. 3 Less weight of the structure. Due to the use of a small amount of materials, weight is reduced, which makes it possible to lay a lighter foundation for the entire structure. 4 Reduced wind load. Due to the lower silhouette, the pitched roof is not so susceptible to windage, and this does not create wind resistance. 5 Equipment for a residential attic (attic) is allowed. With appropriate design of the structure, it is quite possible to create an attic under a pitched roof. 6 Possibility of creating an exploitable roof.However, despite a lot of advantages, such designs also have negative qualities, not always allowing the use of these types of roofs. The main negative properties of single-pitch types of roofing structures are as follows:
- Undesirable use in regions with high rainfall in winter. In other areas of the country, accurate calculations are required, with careful selection of the cross-section of lumber.
It is worth considering that such designs of rafter systems are more appropriate to use in southern regions with low rainfall and constant winds. To the north, you should not build a roof with a slope angle of less than 45 degrees.
- Higher requirements for waterproofing.
- A pitched roof is not always compatible with the chosen style and design of the house.
Despite the disadvantages, pitched roof options are a popular option, especially in low-rise private construction.
Design of pitched roofs. What to consider
When planning the assembly of a pitched roof, you need to take into account and calculate many factors: the layout of the rafter system, the angle of inclination, loads, and select the appropriate materials. The result should be a drawing with complete information about the future roof.
The classic scheme of a single-pitch rafter system consists of beams laid across the structure with fastenings installed along the load-bearing walls. This is a so-called shed roof with simple layered rafters. But this option is only possible for spans with a length of no more than 4500 mm. However, it is permissible to use pitched roofs of greater length.
- With a span width of 5000-6000 mm, the layered rafters need to be reinforced with struts, which rest on a load-bearing wall with an additional Mauerlat.
- If the span width reaches 6000-7500 mm, you will need to assemble more difficult option– with an emphasis on the truss truss. A headstock is added to the design, supporting additional beam, on which the rafter rests. Naturally, the racks (headstocks) are additionally reinforced with struts.
In addition to choosing the layout of the rafter system at the project stage, you will need to plan the step between the beams, as well as their cross-section. Such parameters also depend on the width of the span and the length of the rafters used between load-bearing walls. General recommendations the following:
- When the length of the rafter beam is up to 3000 mm, its cross-section is selected within the range of 80×100 or 90×160 mm. Step between separate elements should be from 1100 to 2100 mm (depending on the cross-section!).
- If the rafter is 6500 mm long, then a beam section of 120×220 mm is selected with a pitch between parts of 1100-1400 mm.
But, in addition to choosing the appropriate section of rafter beams and the assembly scheme, a very important factor is the angle of inclination of the future roof.
Selecting the slope angle
The future functioning of the roof, as well as its strength, depends on the angle of inclination of the assembled slope. The optimal slope should ensure the removal of precipitation from the plane (especially snow), low wind load, and stable fastening of the roof deck.
Calculation of the angles of inclination of all roofing structures must be carried out in strict accordance with SNiP 2.01.07-85 “Loads and impacts”. These building codes provide all the information for a specific region of the country.
It is also worth considering the type of roofing material used, which is also recommended for use at different slope angles. For example, you can use the data from the table below.
Do not forget that in regions with high rainfall in winter, the most optimal location of the slopes is 45°.
When choosing slope angles and roofing material, you need to take into account that planes with slight slopes will have to be cleared of accumulated masses of snow, so it is best to choose a flooring that can withstand the weight of a person without subsequent deformations.
Assembly of various options for pitched roof truss systems
Single slope types truss structures Most often they are used to cover ancillary buildings: garages, sheds and outbuildings. How is the assembly work carried out?
Shed garage roof
Typically, the span width of garages rarely exceeds 4000 mm, so above this building you can use the simplest scheme rafter frame. Assembly is carried out in stages as follows:
- The Mauerlat is made from timber with a cross-section of at least 100×150 mm. The part should not move closer than 50 mm to the outer edge. The element is secured to studs pre-embedded in the masonry. If the structure is made of wood, then the function of the Mauerlat is performed by the upper crown of the walls.
- It is best to prepare a template of the appropriate length for the rafters in advance. Moreover, it is desirable that initially the timber be a little larger (50-100 mm from each edge) from the planned length. The required overhang of the cornices is formed after installing the rafters, cutting off the excess edges. Typically, roof overhangs are made within 400-500 mm on each side.
- Along the entire length of the mauerlat, markings are made for the notch for the rafters. The step between them is in accordance with the project. The wood is sampled to a depth not exceeding 1/3 of the thickness of the timber.
- The manufactured rafters are installed in their places and connected to the Mauerlat using the chosen method (nails, staples, corners, etc.).
- Upon completion of installation, the rafters are trimmed to the required length and covered with a padded wind board.
- To form the roof overhangs in front and behind the garage, you can use two methods.
- The Mauerlat is carried out to the required length beyond the walls of the building.
- Additional elements - fillies - are attached to the outer rafters.
On a note
Accordingly, the sheathing for the roofing is then made!
Formation of the rafter system of the extension
Extensions to a house can have different parameters, and with a span width of less than 4000 mm, you can use the classic scheme with the rafters supported on two load-bearing points. However, with wider buildings (˃4000 mm), it will be necessary to install struts that rest against the wall of the building.
- On external wall In the extension, a mauerlat made of 100×150 mm timber is laid. The part is fastened using the chosen method (on studs, anchors), in wooden building the part is not mounted using the upper crown of the wall as a support for the rafters.
- In the opposite wall of the house, under the rafters, you need to prepare nests to match the size of the rafters in the thickness of the wall (such grooves can be made at the masonry stage).
Shed roofs are successfully used in the construction of utility buildings: garages, sheds, sheds, terraces and gazebos. It's practical and economical way protect the building from precipitation, wind and cold. However, the construction of a pitched roof is also suitable for private houses.
With the help of this construction solution, architects create bold design projects with several slopes of different heights. A huge advantage of roofs consisting of a single slope is its accessibility to the masses of homeowners due to the low price of the materials used and ease of installation.
This article will tell you what the structure looks like, how to calculate the slope of the slope and build it yourself.
Shed roof
Composition of a pitched roof
Most often, the term “single-pitched” refers to a roof that has one slope. The slope, the slope of which is set by a simple rafter system, rests on the load-bearing walls of the building and internal partitions, if any.
The roofing materials used are soft tiles, ondulin, corrugated sheets, metal tiles or euro slate. There are two types of pitched roofs:
- Ventilated. The ventilated roof design is suitable for equipping terraces and gazebos open type, used in summer. The slope of the slope of such a roof varies between 3-6 degrees. The installation of a ventilated pitched roof does not imply insulation, and sometimes even cladding of the gable.
- Non-ventilated. The slope of a roof with one slope of a non-ventilated type is 2-25 degrees, depending on the type of roofing material used. This option is used to cover premises used all year round, residential buildings, heated garages. An unventilated roof is carefully insulated and sealed to reduce heat loss.
The peculiarity of single-pitched roof types is that one gentle slope does not ensure independent melting of snow masses in winter, especially if roofing material with a rough structure was used in construction. Therefore, it is possible that in particularly snowy winters the homeowner will have to take up a shovel.
Strengths of a pitched roof
Increasingly, designers and developers are abandoning complex projects in favor of buildings with a pitched roof. This is easy to explain by its advantages:
- Low cost. Thanks to savings building materials, the installation of a pitched roof is 2-2.5 times cheaper than a gable roof of the same size.
- Simplicity. The single ramp design is simple enough for self-installation. Even with little experience in construction, a novice craftsman can cope with the work alone, having a drawing and the necessary tools.
- High resistance to gusty winds. A pitched roof is the safest option if the construction site is located in an area with permanent rose winds, the main thing is to correctly determine the windward side and orient the slope along it.
- Reduced heating costs. Since the distance between the slope and the ceiling is less than that of other types, the heated rooms do not cool down, which means that heat loss when heating the house becomes less.
- Availability of projects. Even if you are not able to make a drawing yourself, on the Internet and construction literature there are a huge number of ready-made, calculated projects with detailed diagrams of the rafter system and components.
- Easy to maintain. The design of a pitched roof allows you to assess the condition of the rafter system at any time, replace damaged parts, and strengthen the roofing material yourself, without the involvement of hired roofers, whose services are not cheap.
Types of rafter system
System rafter elements roof - a frame that carries and distributes the weight of the roof along the perimeter of the load-bearing walls, giving stability to the structure. Depending on the placement of supports, there are two types of rafters:
The basis for the construction of a hanging or layered rafter system is a detailed drawing reflecting the exact dimensions and relative position of the elements and the method of fastening the main components.
Composition of the rafter system
The scheme of a pitched roof for a structure up to 4.5 m wide, of a layered type, includes a limited number of elements. The basis for the rafter system is a mauerlat made of durable timber 150x150 mm.
It is attached to the top frame of the building along the walls on which the slopes are mounted. To form a roof slope, walls are erected at different heights. The roof also requires rafter legs, which are made from boards measuring 50x150 mm.
At both ends of the board, cuts are made for the Mauerlat. The legs are installed on the mauerlat beam, inserting it into the cuts, fixing it with metal corners.
To evenly distribute the weight of the roofing material across all rafters, installation of sheathing is required. For soft species roofs that are unable to hold their shape on their own use a continuous type of sheathing made of moisture-resistant plywood sheets.
If corrugated sheeting or tiles are used, it is enough to nail 25x50 mm slats across the rafters in increments of 20-13 cm. The complex rafter system of a pitched roof includes a tie, struts, a post and a headstock.
All elements are made from first-grade wood, dried to an optimal humidity of 15-18%, sanded and treated with deep-penetration antiseptic impregnation.
It is important to maintain a balance between the complexity of the rafter system and the cross-section of its elements - by complicating the structure, you increase its weight. The recommended rafter size is calculated based on temporary and permanent loads acting on the roof or determined from tables of ready-made values, taking into account the length and pitch between the legs, and the type of wood.
Calculation of the slope angle
A shed roof is good because, if it is correctly oriented according to the wind rose and the optimal slope is selected, it will withstand strong squally winds, which would destroy a gable roof. To choose the angle of inclination of the slopes, you need to take into account 2 parameters:
Construction installation roof – great option, if you want to quickly and inexpensively cover outbuildings or attach a shed to your house. In addition, this is an excellent opportunity to hone your construction skills without the risk of damaging your roof due to poor quality work.
Video instruction
For construction small buildings and houses there is no need for complex roof configurations. A truss system of a pitched roof can be adopted as a design solution. In this case, the scheme is simplified, but some nuances appear.
Advantages and features of a single-pitched system
The advantages include:
- simple calculation;
- reducing the number of nodes and connections;
- simplified installation;
- reduction in wood costs;
- maintainability.
A pitched roof is resistant to external negative conditions, inexpensive and easy to install
- the need to build high longitudinal walls buildings or special frames;
- the difficulty of using the under-roof space as an attic space;
- it is necessary to locate a house or building on the site so that in most cases the wind blows on the high wall of the building (you need to familiarize yourself with the wind rose of the construction area);
- The angle of inclination is taken depending on the coating material used.
The scheme includes the following main elements:
- two mauerlats;
- rafter legs.
The design of the truss system for a pitched roof
For large spans, you will need a DIY device additional elements, which strengthen the load-bearing beams and increase their load-bearing capacity:
All elements are made from first or second grade coniferous wood. To choose the right one suitable material you need to pay attention to the following points:
- felling location (it is better to choose northern regions);
- time of felling (a tree cut down at the end of winter - beginning of spring will be stronger).
System calculation
Before you start assembling the structure with your own hands, you need to make a calculation and select the correct cross-section of all elements.
Installing a roof is a responsible process in which mistakes should not be made.
Depending on the width of the building and the required section of the rafter leg for the designed span, select constructive solution rafter system.
Calculation of the length of rafter legs
Selection of section
When a house is erected by professional builders according to a pre-prepared project, calculations are made using two limit states, which determines the height and width of the load-bearing beams according to two requirements:
- rigidity;
- strength.
Dependence of the structure on the span
When building a private house with your own hands, you don’t have to perform the calculation, but you need to take into account the recommendations depending on the span. Rafters on a pitched roof are always layered.
- Span up to 4.5 meters. The scheme involves the use of solid rafter legs, without bracing with struts or racks. It is also convenient to use if you plan to install an attic: it allows you to increase free space due to the absence of intermediate supports. The recommended cross-section of the rafters at a pitch of 0.6 m is 50x150 mm; for a pitch of 1.1 m, an increase to 75x175 mm will be required.
- Span up to 6 meters. In this case, everything depends on the angle of inclination and span. In some cases, the standard length of a board or beam - 6 m - is sufficient. With a large angle of inclination and a span approaching 6 m, it will be necessary to join the rafter legs along the length. As additional support, struts (rafter legs) are provided. At the point where the strut joins the rafters, the leg is joined lengthwise. The recommended cross-section at a step of 0.6 m is 50x200 mm, at a step of 1.1 m - 100x200 mm.
- The span is more than 6 meters. In this case, you need to make intermediate racks that will take on part of the load and reduce the sagging of the beam. Correctly install the supports so that each span of the rafter leg is less than 6 meters. In this case, the calculation is performed as for a multi-span beam, taking into account intermediate supports. When building with your own hands, the cross-section is taken in the same way as for a span of up to 6 m (previous point). In this case, all rafters are composite.
If you plan to lay insulation between the rafters yourself (warm attic, attic), then the calculation takes into account minimum height beams
The thickness of the insulation should not be greater than the height of the rafters for polyurethane foam, polystyrene foam and extruded polystyrene foam.
If you plan to install mineral wool, then additionally take into account ventilation gap 5 cm. It is provided partly by the load-bearing beams, and partly by the counter-lattice, which is mounted on top of them.
Selection of beam pitch
The pitch of the rafter legs depends on the following factors:
Table of rafter sections depending on their length and pitch
In the first case, the dependence is inversely proportional. The design of a pitched roof involves reducing the rafter pitch as the span or load increases. For the type of insulation, the following recommended values for the distance between the rafters in the light (clean) can be given:
- polystyrene foam and extruded polystyrene foam - 0.6 m;
- mineral wool - 0.58 m;
- polyurethane foam - the step does not depend on the insulation.
When designing an attic and using skylights as light sources, it will be necessary to ensure that the rafter spacing is 4-6 cm greater than the width of the window in the places where they are installed.
Tilt angle
Depending on the type of roofing used, it is allowed to take different angles slope of the roof slope. Below are the values for the most common materials. It is important to remember that the steeper the slope, the lower the likelihood of leakage and the load on the elements, but this complicates construction and requires the construction of a high longitudinal wall.
- Ceramic tiles. The optimal tilt angle is 30-45 degrees, acceptable is 12-65 degrees.
- Bituminous (soft) tiles. Optimal - 20-45 degrees, acceptable - from 6 degrees.
- Metal tiles. Optimal - 20-45 degrees, acceptable - from 12 degrees.
- Galvanized roofing steel. Acceptable - from 14 degrees.
- Slate. Acceptable - 6-27 degrees.
The smaller the angle of inclination, the lower the consumption of materials for construction, but at the same time the load on the roof and the likelihood of leaks increases.
Work order
After the calculation is completed, we begin purchasing the material and assembling the structure.
- Treating elements with an antiseptic. This can be done after installation in the design position, but if you plan to store the wood, you need to process it immediately after purchase.
- Waterproofing areas of contact between materials with different properties. Where the mauerlats are laid on a brick or concrete wall you need to lay a layer of roofing felt, linochrome or waterproofing.
- Laying the Mauerlat and securing it to the wall. Can be done on wire, staples, studs, anchor bolts.
- Laying rafter legs. Fastening them to the Mauerlat. Can be fastened using staples, nails or corners with self-tapping screws.
- Installation of waterproofing and sheathing.
- Laying insulation.
- Roofing covering.
- Installation of the bottom sheathing and ceiling trim.
It is important to correctly select the scheme of a pitched roof, the cross-section of elements, the pitch of the rafters and the angle of inclination. Compliance with the technology of doing the work yourself will ensure the reliability and durability of the structure.
Rafter system of a pitched roof: diagram
The construction of a pitched roof is easier than other foundations. We will tell you how to calculate and install a truss system for a pitched roof
Rafter system of a pitched roof: structure and fastening
The rafter system of a pitched roof has a number of advantages that make it good choice for installation on auxiliary buildings, garages, extensions to the main building.
Advantages of a pitched roof
Installation of a pitched roof on buildings various types beneficial due to a number of factors:
- low weight of the structure;
- low construction cost;
- simple installation technology;
- possibility of using a wide range of structural and roofing materials;
- ease of installation of the drainage system and chimney.
The roof design with one slope can be used when building a house to implement original design ideas. In addition, this is a favorite option for the roof frame of outbuildings, garages, bathhouses, sheds and verandas.
When building a detached brick garage, the base for installing roofing material can be concrete plates or metal structure. But no less often a rafter system is built from wooden elements. You can calculate rafters for small buildings yourself; in difficult cases, it is recommended to contact professionals.
Rafters: design calculations and material preparation
The construction scheme for a pitched roof is extremely simple: the rafters cover the span between end walls the buildings. The angle of inclination of the slope is determined by the difference in height of the walls. To achieve this difference in height, two methods can be used:
- masonry of one of the opposite load-bearing walls is carried out to a greater height;
- Special supports are mounted on one of the walls, on which a purlin is laid to support the upper ends of the rafters.
The first option is most suitable when constructing a structure from piece materials. The second method allows you to save building materials from which walls are built.
A roof structure with one slope should have a slope of no more than 50-60°. Optimal value an angle of 18-35° is considered, but specific parameters should be selected taking into account various factors. The rafter system must withstand its own weight and high external loads - wind and snow. The intensity of the loads directly depends on the angle of the slopes. In addition, you should pay attention to the values at which installation of the selected roofing material is possible.
The pitch of the rafters also affects the reliability of the roof. The smaller the pitch, the higher the calculated load that the roof can withstand. But if the installation step of the rafter legs is unreasonably small, this leads to an increase in the weight of the structure, and, accordingly, the load on the walls and foundation of the building. Too large a rafter pitch will not allow you to create a roof that is resistant to external influences.
The design calculation can be performed manually, but it is more convenient to do this using special program. The developed project should reflect not only the pitch, dimensions and sections of the elements, but also the execution diagrams of the roof frame components.
The rafters of a pitched roof for small spans are made of boards or beams. If the span exceeds 4.5 meters, extended rafter legs may be necessary.
Timber and boards for the manufacture of a rafter system for a garage or other building must be well dried and free of damage that affects the strength characteristics. Before installation, prepared wooden elements must be treated with a fire-retardant compound to protect the frame from accidental fire and extend its service life.
Installation diagram of garage roof rafters
The truss system of a garage roof during the construction of a lean-to structure may vary depending on the characteristics of the building. On a small structure, it is enough to simply lay the rafters, resting them on the top of the opposite walls, made of bricks or blocks. If the construction of a garage with an attic is planned, then in this case it is necessary to lay beams across the span (step - 1-1.5 m), which will serve as the basis for the floor. The rafters, as in the first case, are attached to opposite walls, but are additionally reinforced with struts - this allows for the necessary rigidity of the garage roof frame.
If the box of the structure is constructed of brick, the ends of the beams and rafters of the garage shed roof can be laid in special nests provided in the walls. In this case, the beams are attached to the long walls, and the rafters are attached to the end walls. The tall wall should be the wall with the garage door. Waterproofing made of rolled bitumen-containing material is pre-installed into the nests.
Wooden rafters for a pitched roof can be mounted directly on the walls of the structure if a small span is being covered and the pitch of the rafters is sufficient to accept and distribute the load fairly evenly. In other cases, the rafter legs are attached to the mauerlat.
The requirements for the Mauerlat are quite simple: it must be strong, durable, firmly attached to a wall built from piece building materials. Theoretically, the rafters should be attached to the Mauerlat mounted on reinforced belt walls. But since the garage is a building with light loads, the support beam under the rafters can be laid directly on the upper edge of the wall and secured with anchors and rolled wire embedded in the masonry. Mauerlat requires reliable waterproofing made from rolled materials.
The reinforced belt of the wall under a pitched roof is made of reinforced concrete. To equip it, you need to make plank formwork, secure reinforcement in it and install studs. The height of the embedded fasteners should allow subsequent laying of a mauerlat beam with pre-drilled holes for studs on top of the monolithic beam and fastening with nuts equipped with wide washers.
If a garage or other building is built from timber or logs, the function of the mauerlat is performed by the top frame of the log house. The installation pitch of rafter legs on a pitched roof is most often 60-70cm - this parameter makes it possible to use almost any piece or roll material for the roof, provided that the appropriate type of sheathing is installed.
In order for the rafter system to allow the installation of a roof that can protect building structures from the effects of precipitation, the rafter legs must protrude 30-40 cm beyond the edge of the wall, forming an overhang.
Installation of the extension roof
A residential or commercial extension is a building adjacent to the main building. Most often, a pitched roof is erected over it, adjacent to the wall of the main building or its roof. Fastening the rafters of a lean-to roof of an extension differs to some extent from installing a roof frame on a free-standing structure. The main difference concerns the installation of the upper part of the rafters - the lower ends of the rafter legs are attached to the Mauerlat or a special support using standard methods.
Before erecting a shed roof for an extension, it is important to determine the required slope angle. In accordance with the obtained value of the required difference between the front wall of the extension and the rear, a wooden structure made of timber with a cross-section of at least 150×150 mm is mounted. Special attention it is necessary to pay attention to the connection of the frame for the rafters with the wall of the main building.
It is not recommended to use rigid fastening, since adjacent buildings may have different shrinkage rates, which over time will lead to the formation of cracks in the walls. The construction of such a ligament usually involves the use of an elastic layer between the support beam for the rafters and the wall. The beam can be laid on columnar supports or a timber frame. A gap of 2-3 cm between the beam and the wall ( expansion joint) should be filled with polyurethane foam or other elastic material with low thermal conductivity. It is allowed to attach the beam to the wall using anchors.
If it is required that the roof of the extension adjoins not the wall, but the roof of the main building, it is advisable to think in advance about what technology will be used to install the rafter system. To ensure maximum reliability of the shed roof of a new building, it is recommended to completely dismantle the adjacent roof slope of the main building in order to install new rafters from the ridge of the main roof to the extension's mauerlat. It is necessary to provide for the extension of the rafters beyond the plane of the extension wall for the installation of a cornice. Another option involves connecting the rafters of the extension to the rafters of the main roof at a certain distance from its ridge. In this case, the roof joining device requires the dismantling of only part of the main roof slope.
When choosing the angle of inclination of the roof of the extension, you should pay attention to the following points:
- the greater the angle of inclination of the rafters, the less the danger of accumulation of rainwater or snow mass that has “moved” from the main roof;
- rafters of the extension located with south side, may have a smaller slope than a similar design with north side, because The sun promotes intense evaporation of moisture.
Wooden rafters for a pitched roof are sensitive to moisture. The junction of the rafter legs to the wall or main roof should be carefully sealed - for this purpose, a roofing apron is installed.
Rafter system of a pitched roof: how to install, fastening, device
Construction and fastening of a rafter system for a pitched roof. Design, installation and selection of rafter spacing for a pitched roof of a house, garage or extension.
How to install a pitched roof rafter system - rafter installation guide
Among the wide variety of roof types, the simplest and most economical is the shed roof. The design requires a minimum amount of materials with simple installation technology. Building a pitched roof can be a good lesson for a novice roofer. But success even in a simple matter can only be achieved if strict technological requirements are observed. To ensure quality work and reliability of the roof, you need to know the features and basic rules for installing a pitched roof truss system.
Roofs with one slope for low-rise construction
Shed roofs are most often used in the construction of small-sized buildings, such as terraces, garages, verandas and domestic premises. On residential buildings Such a roof can be seen very rarely; most often these are buildings in the Art Nouveau and high-tech styles.
The attic space under a pitched roof has small area, so it is very difficult to arrange a room in this space. In this case, the question may arise as to whether it is necessary to make a ceiling between the attic and the main building. If the ceiling is not practical, then you can replace it with spacers and rafter legs. This option is very often used by builders in practice.
In general, the rafter system of a pitched roof is similar to a floor laid at an angle or half of a layered system, that is, it is structural element buildings. For its construction, layered rafter legs are required. In other words, the frame of a pitched roof is constructed from rafters that have strong support at the top and bottom.
The following can be used as support for the rafters of a pitched roof:
- Two load-bearing walls. In this case, the intermediary between the elements of the rafter system and the walls can be a double Mauerlat, an upper beam or log of a wooden structure, or a reinforced concrete belt, which must be installed during the construction of the walls.
- One load-bearing wall and opposite supports. This method is used in the construction of extensions and sheds. The support of the upper heel of the rafter leg falls on a steel bracket, which is screwed to the load-bearing wall, or on a socket selected in the load-bearing wall. At the bottom, the rafter rests on the harness support pillars.
- Two rows of supports. The support for the upper and lower heels of the rafter legs is the strapping of the support posts. In this case, you can use supports as elements for fastening the sheathing and forming the frame.
In private construction, small buildings are most often found, so it is worth taking a closer look at the structure of the truss system of a pitched roof. If you understand this issue, you can do all the work yourself, making the necessary additions and changes.
When drawing up a diagram of the rafters of a pitched roof, it is worth taking into account the direction of the wind and positioning the slope so that a strong gust does not blow off the roof.
Approximate parameters of pitched roof elements
Layered rafters can be made from grade 2 lumber. Most often these are round hewn logs, plates, which are a log, timber or boards hewn on both sides, sewn together in pairs.
The cross-section of the rafters is determined by the load on the roof from wind, snow and roofing. To determine the parameters of the elements of a pitched roof, you can use a computer program.
But in most cases these values are constant:
- A rafter frame covering a span of more than 4.5 meters should be constructed from logs and plates with a diameter of 18-20 cm and timber with a cross-section of 10*15 cm or 15*15 cm.
- For smaller spans, you can build a frame from logs and plates with a diameter of 12-18 cm and a beam with a cross-section of 10*10 cm.
In both cases, it is possible to replace the timber with double boards, the final size of which is similar to the required cross-section of the beam.
It is very important to understand that rafter systems for pitched roofs should not be constructed from smaller components. Even for minor buildings, the specified parameters are the lowest limit.
To make a Mauerlat, it is recommended to use timber with a cross-section of 18-20 cm. For struts on long roofs, it is allowed to take timber with a cross-section of 8*8 cm, logs with a diameter of 10 cm or double boards, the final size of which is 2.5*15 cm.
The purlins of long-span single-pitched roofs are arranged parallel to the slopes. In this case, they are used as additional support and increase the strength characteristics of the structure. To fasten the purlins, install supports and beams, relying on the technology of constructing a gable roof. In this case, it is not the formation of the ridge that occurs, but the support of the plane of the long slope is provided. To make purlins, a timber with a cross-section of 18*18 cm or a log with a diameter of 20-26 cm is used. Racks for purlins can be made from a timber with a cross-section of 12 cm or a log with a diameter of 13-20 cm. In this case, you can use different ways fastening the rafters of a pitched roof.
Distance between rafters of a pitched roof
The rafters are installed at a certain distance from each other, which depends on the size of the box over which the roof is being erected. The slope, which will serve as a support for the rafters, must be divided into segments so that the elements of the system are located at the same distance from each other. In this case, you should take into account the dimensions of the materials used and their type:
- If timber or plates were used to make rafters, then the distance between them should be 1.5-2 meters.
- When using double boards, the rafters are spaced in increments of 1-1.75 meters.
- If the rafters are made of a single board, then the distance is reduced to 0.6-1.2 meters.
If you plan to build an insulated roof, then the distance between the rafters may be affected by the size of the insulation. Thermal insulation material should fit very tightly between the elements of the rafter system. In this case, the formation of cold bridges is eliminated, which leads to a reduction in heat loss. Read also: “How to install the rafters of a pitched roof - rules for calculation, installation and fastening.”
When determining the pitch between the rafters, you should pay attention to one more point: increasing the set pitch leads to additional costs for the sheathing. In this case, it is allowed to use a continuous version or with a small step. Therefore, even at the design stage, it is necessary to determine what is more profitable: frequent lathing or a larger number of rafter legs.
As with all pitched roofs, the rafters of a pitched roof are secured using anchor bolts, laid into the wall during their construction, or crutches that are driven into a wooden wall. In addition, every second rafter is fixed with twisted annealed wire. The rafters are fastened to the wall at a point located 0.2-0.3 meters below the Mauerlat. The wire is attached depending on the material used to build the walls. In brick walls, the twist is laid during the laying process, to wooden walls the wire is secured with staples.
To better understand the structure of the rafters of a pitched roof, it is worth taking a closer look at the installation options for such structures.
Fastening rafters for a pitched garage roof
Very often, garages are built from foam concrete blocks, so you should find out how the rafter system is designed in this case. If a reinforced concrete belt is not poured at the top of the walls, then a mauerlat must be laid. Single-pitch roofing system involves the use of timber laid on the front and rear walls of the garage, which have different heights.
When solving the problem of how to properly install rafters on a pitched roof, you need to adhere to the following order:
- A beam with a cross section of 10*15 cm is laid flush with the inner surface of the walls. As a result, a roof plate with one slope is formed. To protect wooden elements from the effects of foam concrete, they should be laid on a waterproofing material. To fasten the Mauerlat, it is recommended to use roofing corners measuring 9*9 cm, installing the fastening at a distance of 0.8 meters. Additionally, they can be strengthened with a cast lintel. The corner is attached to the wall with dowels with a diameter of 14 mm.
- A template of rafter legs is made using a 5*20 cm board. The length of the rafters of a pitched roof is determined as follows: the workpiece is installed on the mauerlat, leaving a margin of up to half a meter at the top and bottom. This margin should slightly exceed the standard width of the eaves overhang, 0.4-0.5 meters. After installing all the rafters, the excess sections are cut off.
- Mark the insertion points on the rafters, remembering that the insertion should not be very deep. Most often, this parameter is a third of the width of the board.
- Mark the walls, making sure that the distance between the rafters and the wall is at least 5 cm.
- Using a template, make rafters for the entire roof, install and secure them with brackets or corners.
- Determine the width of the overhang and make a filly template. To do this, you can use cutting boards. Ready template used for the manufacture of all cornice elements. When installing them, be sure to lay a waterproofing material to prevent contact of the wood with the concrete wall.
- The size of the rafters for a pitched roof is equalized and a wind board is nailed along the entire perimeter, using material measuring 2.5 * 10 cm.
- The rafter system for a pitched roof over a garage made of foam concrete blocks is considered ready. Next, the sheathing is placed on the rafters, determining the pitch depending on the roofing material.
In the variant under consideration, the eaves overhangs were formed using fillets. You can use another option, which involves moving the Mauerlat outside the perimeter of the building. The offset is determined by the width of the eaves overhang. The length of the rafters in this case also increases by the width of the overhang. Between the two outer rafters it is necessary to make an extension. All other actions are performed according to the standard plan.
Installation of a lean-to rafter system over an extension
Very often there is a need to make an extension to the main building. To match the additional structure general exterior It is recommended to make a pitched roof. In addition, this design will not retain precipitation.
The rafter system in this case should have a slope of about 20 degrees. The support for the rafter legs will be the load-bearing wall of the house and the opposite wall of the extension. If the extension is more than 4.5 meters long, then it is necessary to install struts that will provide rigidity to the rafter system. It is recommended to install the struts at an angle of no more than 45 degrees.
To make rafter legs, 5*20 cm boards are used, which are installed in increments of 0.7 meters. The struts can be made from boards measuring 5*15 cm, but for lathing it is better to choose boards 2.5*10 cm.
The construction of a rafter system with one slope is as follows:
- On brick wall extensions, waterproofing material is laid, and a beam with a cross-section of 10*15 cm is installed on top of it, flush with the inner plane of the wall. The beam is fixed with bolts installed at intervals of 8-10 cm.
- Grooves are made in the load-bearing wall of the house, 12 cm deep and slightly wider than the thickness of the rafters. The distance between the grooves should be about 0.7 meters. Another answer to the question of how to secure rafters on a pitched roof can be the use of U-shaped metal brackets fixed to the wall.
- A rafter template is made from a board measuring 5*20 cm.
- All rafters are made using templates and installed according to the grooves or brackets made. Top part It is attached with metal corners, screwed on one side to the wall and the other to the rafter. At the bottom, fixation is performed with staples or corners.
- Using a scrap of board, make a strut template. It should be remembered that the angle of inclination should not exceed 45 degrees, and the stop at the bottom should be placed below the height of the opposite wall by 0.2-0.3 meters.
- To determine the location of the grooves for the struts, you need to visually draw a vertical line from the top groove and step back 5 cm in any direction. The grooves should also be spaced 0.7 meters apart.
- To install the strut in the groove, you need to cut the lower corner of the strut. In this case, the cut size should be 0.1 m.
- To determine the line of the top cut, the strut is installed in the groove, and the top is applied to the rafter. The place of their intersection is determined by the upper cut.
- Using this template, you need to make the remaining struts and install them using metal toothed plates.
- The cornices are formed using fillies installed on the inclined walls of the extension. Waterproofing must be installed under the fillies.
- Next, the rafter system is sheathed with a wind board along the entire perimeter and the sheathing is hammered on.
According to the above diagram, you can install a single-pitched rafter system over verandas and utility blocks.
How to secure a lean-to rafter system over a barn
Small outbuildings and summer kitchens do not need a powerful roof, so it is better to use a pitched roof for them. For example, you can consider the diagram of the rafter system of a pitched roof over a shed intended for storage gardening tools. This building is made according to the principle of constructing a frame for greenhouses, in which the vertical posts are connected by strapping around the perimeter. The front wall is slightly higher than the rear wall, so the racks are connected by separate crossbars.
The algorithm for installing a rafter system for a pitched roof over a barn involves performing the following actions:
- Make a template for the rafter leg. To do this, apply the board to the end and mark the places where the cuts are made at the top and bottom.
- The rest of the rafters are made using the templates. Make markings on the walls of the shed and fix the rafter legs. When constructing lightweight buildings, it is enough to use nails or self-tapping screws.
- The wind board is nailed after installing the sheathing around the perimeter of the building.
The examples given can be used as a basis for individual designs, so the structure of a single-pitch rafter system must be known in detail.
Rafter system of a pitched roof: fastening of rafters, diagram, how to fasten, install correctly, device, system size, length, installation
Rafter system of a pitched roof: fastening of rafters, diagram, how to fasten, install correctly, device, system size, length, installation
Construction of a truss system for a pitched roof
The rafter system of a pitched roof refers to simple designs. It attracts with its reliability and economical consumption of material. The construction of a pitched roof is permissible on your own and can be completed in a short time.
It is popular for garages, outbuildings and sheds. Residential buildings are less often covered with a roof with one slope, but such options are found when implementing original architectural ideas for constructing a building. Despite the simplicity of the design, the work on creating a roof is a very important stage and requires adherence to technology.
Rafter frame of a lean-to structure: installation nuances and elements
The layout of the rafter system for a small building is quite simple: inclined rafters laid on the mauerlat cover the distance between the end walls. The span of the building in this case is no more than 4.5 m. The angle of inclination of the slope is determined by the difference in the height of the opposite walls. This can be achieved in two ways:
install special supports on one of the walls under the upper edges of the rafters;
when laying load-bearing structures, one should be built higher than the other.
When the slope is oriented, the low part of the roof is directed towards constant winds, this will ensure the resistance of the frame to high loads.
The function of the rafter frame is to redistribute constant and emerging loads on the roof between load-bearing walls. Her constituent elements are:
- Mauerlat - a beam at the base of a structure connecting it to the walls of the structure;
rafters - a board or beam that forms the basis of the frame;
- struts, racks, supports - elements that strengthen the structure with a span of 6 to 9 m;
- sheathing - slats, packed at a distance determined by technology, are the basis for the roofing and strengthen the rafter system.
A single-slope structure is characterized by less windage than systems with a large number of slopes, but when designing it, it is necessary to take into account the weight of the snow cover. This is especially true for roofs with a small slope of 8-10 degrees. When creating drawings, the location and size of all elements of the rafter system, as well as installation diagrams for frame components, are noted.
The distance between the rafters of a pitched roof is recommended within 60-80 cm, this ensures sufficient strength for any coating used. The presence of overhangs 25-40 cm long on each side of the building guarantees the drainage of rainwater from its walls, eliminating their erosion.
Advantages of a pitched roof
- The consumption of lumber is significantly reduced compared to more complex structures.
- Construction costs are reduced.
- Large selection of roofing materials as a finishing coating.
- You can install the rafter system yourself in a short time.
How is the angle of inclination determined?
The slope of the slope is one of the main parameters of the roof. The intensity of the load on the rafters directly depends on this indicator. Main selection criteria:
- Amount of precipitation in the region.
- Type of roofing.
A large angle contributes to the unhindered melting of snow, but leads to additional consumption of material. A slight slope reduces the impact of wind, but requires frequent clearing of snow from the roof. The optimal angle is also related to the type of roofing; for each material there is a recommended parameter in degrees:
- metal tiles - 25;
- slate, ondulin - 20;
- roofing felt and other rolled materials - from 5 to 10;
- corrugated sheeting - 20;
- natural tiles - 35.
Preparation of lumber before installation
The service life and reliability of the roof depend on the quality of the lumber used in the construction of the frame. It is recommended to use dry softwood timber. The wood should not have knots or damage. Before installation, it undergoes mandatory treatment with an antiseptic and fire retardant; these compounds protect against rotting and fire. The size of the beam depends on several factors:
- span length;
- the amount of load on the roof (snow, wind, etc.);
- slope angle.
The section of boards for rafters is 50×150 mm, 60×180 mm, timber for mauerlat 150×150 mm, for lathing 50×50 mm. 
Stages of installation of the rafter system
The construction of the frame begins with laying the Mauerlat. Before installation on the walls, the timber is wrapped in roofing felt for waterproofing. The base is attached to the studs laid during laying or using anchor bolts.
The rafters are installed on a fixed Mauerlat. For strong fixation, it is necessary to make cuts on the boards. To ensure that all inserts are the same size, they are made according to a template. The upper part is sawn with a bevel, allowing the rafters to bend. The lower notch serves as a strong support for the Mauerlat.
The roof rafters are fastened using nails and corners screwed with self-tapping screws. You can simplify the installation of the frame by installing the outer rafters and stretching a rope between them to define the plane.
If the length of the purlin is more than 4.5 m, the brace is installed at an angle of 45 degrees, one of its edges rests on the rafter, and the other on the mauerlat.
The end of the installation will be filling the sheathing. Its bars are located perpendicular to the frame, the fastening step depends on the finishing coating. A continuous sheathing is made under the rolled material. Moisture-resistant plywood or OSB boards are used for covering.
After installing the rafter system, a waterproofing sheet is laid and the roof is insulated. The final stage of work is installation of the roof covering.
Once a week we send a digest with the most popular articles.
I consider the shed roof system to be the most acceptable option for arranging a garage or shed. A person with minimal knowledge in construction will be able to install such a roof system. Just don’t exaggerate your capabilities and knowledge in construction.
Installation and sekhma of the truss system of a pitched roof
What parts does a pitched roof consist of, preparation of materials and components. Installation procedure and important nuances, which you need to know about.
For the construction of small buildings and houses there is no need to install a complex roof configuration. A truss system of a pitched roof can be adopted as a design solution. In this case, the scheme is simplified, but some nuances appear.
Advantages and features of a single-pitched system
The advantages include:
- simple calculation;
- reducing the number of nodes and connections;
- simplified installation;
- reduction in wood costs;
- maintainability.
When deciding to make such a roof with your own hands, you need to take into account the following features:
- the need to erect high longitudinal walls of the building or special frames;
- the difficulty of using the under-roof space as an attic space;
- it is necessary to locate a house or building on the site so that in most cases the wind blows on the high wall of the building (you need to familiarize yourself with the wind rose of the construction area);
- The angle of inclination is taken depending on the coating material used.
The scheme includes the following main elements:
- two mauerlats;
- rafter legs.
For large spans, you will need to install additional elements yourself to secure the load-bearing beams and increase their load-bearing capacity:
- rafter legs (struts);
- racks;
- runs;
- lying down;
- contractions.
All elements are made from first or second grade coniferous wood. To correctly select the most suitable material, you need to pay attention to the following points:
- felling location (it is better to choose northern regions);
- time of felling (a tree cut down at the end of winter - beginning of spring will be stronger).
System calculation
Before you start assembling the structure with your own hands, you need to make a calculation and select the correct cross-section of all elements.
Installing a roof is a responsible process in which mistakes should not be made.
Depending on the width of the building and the required section of the rafter leg for the designed span, a design solution for the rafter system is selected.
Selection of section
When a house is erected by professional builders according to a pre-prepared project, a calculation is performed based on two limit states, which determines the height and width of the load-bearing beams according to two requirements:
- rigidity;
- strength.
When building a private house with your own hands, you don’t have to perform the calculation, but you need to take into account the recommendations depending on the span. Rafters on a pitched roof are always layered.
- Span up to 4.5 meters. The scheme involves the use of solid rafter legs, without bracing with struts or racks. It is also convenient to use if you plan to install an attic: it allows you to increase the free space due to the absence of intermediate supports. The recommended cross-section of the rafters at a pitch of 0.6 m is 50x150 mm; for a pitch of 1.1 m, an increase to 75x175 mm will be required.
- Span up to 6 meters. In this case, everything depends on the angle of inclination and span. In some cases, the standard length of a board or beam - 6 m - is enough. With a large angle of inclination and a span approaching 6 m, it will be necessary to join the rafter legs along the length. As additional support, struts (rafter legs) are provided. At the point where the strut joins the rafters, the leg is joined lengthwise. The recommended cross-section at a step of 0.6 m is 50x200 mm, at a step of 1.1 m - 100x200 mm.
- The span is more than 6 meters. In this case, you need to make intermediate racks that will take on part of the load and reduce the sagging of the beam. Correctly install the supports so that each span of the rafter leg is less than 6 meters. In this case, the calculation is performed as for a multi-span beam, taking into account intermediate supports. When building with your own hands, the cross-section is taken in the same way as for a span of up to 6 m (previous point). In this case, all rafters are composite.
If you plan to lay insulation between the rafters yourself (warm attic, attic), then the calculation takes into account the minimum height of the beams.
The thickness of the insulation should not be greater than the height of the rafters for polyurethane foam, polystyrene foam and extruded polystyrene foam.
If you plan to lay mineral wool, then additionally take into account a ventilation gap of 5 cm. This is partly provided by the load-bearing beams, and partly by the counter-lattice, which is mounted on top of them.
Selection of beam pitch
The pitch of the rafter legs depends on the following factors:
In the first case, the dependence is inversely proportional. The design of a pitched roof involves reducing the rafter pitch as the span or load increases. For the type of insulation, the following recommended values for the distance between the rafters in the light (clean) can be given:
- polystyrene foam and extruded polystyrene foam – 0.6 m;
- mineral wool – 0.58 m;
- polyurethane foam - the step does not depend on the insulation.
When designing an attic and using skylights as light sources, it will be necessary to ensure that the rafter spacing is 4-6 cm greater than the width of the window in the places where they are installed.
Tilt angle
Roof slope angle Depending on the type of roofing used, it is allowed to take different angles of inclination of the roof slope. Below are the values for the most common materials. It is important to remember that the steeper the slope, the lower the likelihood of leakage and the load on the elements, but this complicates construction and requires the construction of a high longitudinal wall.
- Ceramic tiles. The optimal tilt angle is 30-45 degrees, acceptable is 12-65 degrees.
- Bituminous (soft) tiles. Optimal - 20-45 degrees, acceptable - from 6 degrees.
- Metal tiles. Optimal - 20-45 degrees, acceptable - from 12 degrees.
- Galvanized roofing steel. Acceptable - from 14 degrees.
- Slate. Acceptable is 6-27 degrees.
The smaller the angle of inclination, the lower the consumption of materials for construction, but at the same time the load on the roof and the likelihood of leaks increases.
Work order
After the calculation is completed, we begin purchasing the material and assembling the structure.
- Treating elements with an antiseptic. This can be done after installation in the design position, but if you plan to store the wood, you need to process it immediately after purchase.
- Waterproofing areas of contact between materials with different properties. In the place where the mauerlats are laid on a brick or concrete wall, you need to lay a layer of roofing material, linochrome or waterproofing.
- Laying the Mauerlat and securing it to the wall. Can be done on wire, staples, studs, anchor bolts.
- Laying rafter legs. Fastening them to the Mauerlat. Can be fastened using staples, nails or corners with self-tapping screws.
- Installation of waterproofing and sheathing.
- Laying insulation.
- Roofing covering.
- Installation of the bottom sheathing and ceiling trim.
It is important to correctly select the scheme of a pitched roof, the cross-section of elements, the pitch of the rafters and the angle of inclination. Compliance with the technology of doing the work yourself will ensure the reliability and durability of the structure.