There are two types of attic structures: with a sloping roof, as a rule, these are alterations of non-residential attic spaces and with a sloping roof, which is provided for by the design of the house and was designed from the beginning. The use of the second type is preferable, as it provides more usable space. However, the design and calculation of a broken-type mansard roof is much more complicated. This article will show how, using special online calculators, to obtain the basic parameters of a mansard roof: the number and cross-section of the main load-bearing elements, the angle of inclination of the side and hanging slopes, type roofing material, as well as the approximate cost and quantity of building materials.
What you need to know to make calculations
On the Internet you can find many online calculators with which you can calculate the attic roof. They can be specialized - for calculating the cross-section of the main load-bearing elements, usable area premises, the angle of inclination of the slopes or the distribution of the load on the rafter legs or universal ones. Use the second type of online calculators for non-specialists in construction industry quite difficult, since these programs will require much more initial data for calculation and operate with such specific terms as Mauerlat, struts, rafters, etc.
Let us highlight the main structural elements, the dimensions and quantities of which should be given by the attic roof calculator:
Rafter legs
The main load-bearing element of the roof structure. For residential buildings, most often, round or round beams are used as the material for making rafters. square section. Is it allowed to use? both solid wood and laminated timber. There are two types of rafters:
Layered(from the word lean) the lower ends are installed on the wall of the building, in the middle part they rest on intermediate supports. They are used in sloping roof structures if the span width between the load-bearing base exceeds 4.5 m;
Hanging– are used if the structure does not have internal load-bearing elements: columns, walls, beams on which additional supports can be located. The maximum span width is 6.5 m. Hanging rafters form sloping roofs and are not very convenient for creating attic floors.
Racks
Additional load-bearing elements (pillars) that give the roof structure additional strength. In the attics small area with a simplified design, they rest on the floor slabs and directly support the rafters. In more complex structures of attic roofs, the racks rest on the beams and act as a load-bearing base for the purlins;
Mauerlat
One of the most important elements rafter system. Designed for transition from concrete or brick wall to wooden structures. Simply put, this is a beam with a cross-section from 150x100 mm to 200x200 mm, which is laid on the load-bearing wall along it and is the main support for the rafter legs. Coniferous wood is used as manufacturing material. Particular attention must be paid to protecting the element from moisture and mold, as well as waterproofing between the wall and the Mauerlat.
Lezhny
In fact, this is the same Mauerlat, but located not on the wall, but on attic floor. Its main purpose is to distribute the load from the racks over a larger area. That is, the racks will not put pressure on the attic floor at one point with dimensions of 150x150 mm (which can cause damage to the ceiling). The bench distributes the pressure from the racks over a large area, similar to how skis distribute the weight of a person, and he does not fall into the snow.
Run
A load-bearing element designed to support rafters. It is used if the roof slope is long and/or the roofing material has significant weight.
On our website you can get acquainted with the most . In the filters you can set the desired direction, the presence of gas, water, electricity and other communications.
Calculation of various elements of the attic roof
You can calculate the area of the attic roof using two types of calculators. The first one is an application written in some kind of calculation program, the most popular is Microsoft Excel. This type of calculator is quite complex, as it requires not only knowledge in the construction industry, but also some experience in using Excel. However, it can be used to make fairly accurate calculations.
The second type of applications are small online calculators posted on the websites of companies involved in construction or the sale of building and roofing materials. The accuracy of such calculations is relative, but they can guide the buyer on the approximate amount he needs to expect when building an attic.
Dependence of the steepness of the lower slope on the height of the room
The calculator calculates the angle of inclination of the lower attic rafters at a certain width of the house and planned ceiling height. In order to calculate the attic roof, the following data is required:
Size walls under the pediment - Vd;
Height premises – Nm;
Width premises - Vm;
Width“dead” area of the attic - Vg;
Height skate - Nk.
The calculation is carried out using a simple geometric formula Вг=Нв/tg α. As a rule, such applications specifically limit the possibility of entering incorrect data.
The calculator makes it possible to calculate several quantities at once: the offset of the floor beams and the angle of inclination of the attic rafters. The calculation can be made both by entering the height of the room and the angle of inclination of the side rafters, and also by reverse order. By specifying the required dimensions of the room, you can obtain the angle of inclination - α, of the side (lower) rafters.
Calculation of the height and angle of inclination of ridge slopes
This calculation sloping roof necessary to obtain the overall height of the house. It is necessary to take into account that the angle of inclination of the rafters of the ridge slope, as a rule, is taken within the range of 15°-30°.
The calculation formula will be as follows: Нк=Вм×tg β
The calculator will require you to indicate the width of the attic space and the planned angle of inclination of the ridge rafters. It is also possible to solve the inverse problem by indicating the total height of the entire building and the planned ceiling height attic floor the program will calculate the angles of inclination of the ridge and side rafters.
Calculation of the length of the rafter leg
Regardless of whether the rafter is part of the lower or ridge cattle, the calculation formula is the same in both cases: L=H/sinα(β), where
L- length rafter leg;
N– either the height of the attic space Nm, or the height of the ridge segment Hk.
α/β – the corresponding angles of inclination of the stops.
Calculation of loads on the roof structure and determination of the optimal cross-section of rafter legs
The main load on the load-bearing elements of the roof comes from the roofing material, as well as snow and wind loads. At the same time, a safety margin is laid down in case natural disaster, for example, hurricane winds atypical for the area. When selecting a section, they operate with the concept of distributed load. This value depends on the number of rafters, respectively, on the step of their installation - the smaller it is (the more rafter legs are used), the smaller the cross-section of each element will be.
The calculator for calculating the rafter system of an attic roof is more complex and will require information not only about the angle of inclination of the roof slopes, but also about the location of the structure on the ground, and about the region of construction in order to determine the level of snow and wind load.
Roofing type
On this moment The most popular roofing materials for the construction of an attic floor are:
Metal tiles– characterized by high strength, resistance to mechanical damage, fading, and temperature changes. Provides a wide selection of reliefs and a rich color palette;
Roofing corrugated sheets– the main performance indicators are similar to metal tiles, however, the decorative possibilities are very limited. The building is mainly used as a roof for industrial and technical purposes;
Pulp-bitumen sheets (ondulin) - has a limited service life (15-20 years), fades in the sun, and becomes brittle under the influence of frost. In its normal state it also exhibits rather low mechanical strength;
Ceramic tiles– has high aesthetic and performance indicators, however, the large weight of the roofing material makes it necessary to use reinforced truss structure.
Video description
In the video you can see the calculation of the attic roof:
Snow and wind loads
Snow and wind load zones are determined using special maps. Depending on the zone in which the house is located, certain coefficients are substituted into the attic formula when calculating.
Calculation of insulation thickness
The thickness of the heat is calculated in the same way insulating material for the attic. Using a special map, the thermal resistance coefficient in the construction region is selected - this value is supplied to the program, after which the type is indicated thermal insulation material, as well as material for interior decoration indicating the thickness of the skin.
Calculation of roofing area
Calculating the roof area is an elementary task, for which universal calculators do not even have a separate function. As a rule, roofing calculators are used exclusively by websites selling roofing materials. The calculation is carried out using the following formula: S=2×D×(Lm+Lk), where
S– total roof area. When purchasing roofing material, it is necessary to take into account the specifics of its installation. In fact, for each type of roofing there is a coefficient or percentage by which you need to increase the amount of roofing material when purchasing.
D– Roof length along the eaves or ridge line;
Lm– Length of the rafters of the lower overhang of the attic;
Lk Ridge rafter length.
Video description
In you can see the design diagram of the attic:
Conclusion
It is important to consider that the area, cross-section and type of sheathing are selected individually for each roofing material.
It is even more important to understand that the data provided by online calculators of any type are inaccurate, they are only suitable for the home owner to be able to navigate the choice construction company contractor.
To calculate the dimensions, area, materials and rafter system of the attic, enter the values in millimeters (mm):
Y– The height of the upper, usually flatter part of the roof slope. Meaning Y accepted small (up to 1500 mm).
X– Half the width of the roof, (i.e. the width of the entire roof is 2 X), depends on the width of the building.
C– the size of the eaves overhang (the overhang is necessary to protect the walls and foundation from precipitation) is determined taking into account the climatic characteristics of your region (SP 20.13330.2011) and the general architectural design.
For one and two-story houses with drainage system minimum size C– 400 mm (according to SNiP II-26-76*), without organizing external water drainage, not less than 600 mm. The optimal overhang is approximately 500 mm.
B– The length of the roof is determined by the length of your house.
Y2– The height of the lower, steeper part of the roof slope. From value Y2 depends on the height of the room in the attic floor, which is generally taken to be about 2500 mm. The choice of parameter must be justified in accordance with SNiP 2.08.01-89* “Residential buildings”.
Building materials for roofing:
S1 And S2– Width and Thickness of the rafters. Selecting parameters S1 And S2 is carried out taking into account the loads acting on the rafter (constant, temporary and special) and depends on the quality and type of material used (timber, board, laminated veneer lumber), the length of the rafter leg, the distance between the rafters. When determining the width and thickness of the rafters for an attic roof, follow the recommendations given in SP 64.13330.2011 “ Wooden structures"", SNiP II-26-76* "Roofs" taking into account SP 20.13330.2011 "Loads and impacts".
S3– The distance between adjacent rafters (often called the rafter pitch or run).
Approximate section of timber and step ( S3) for rafters of various lengths can be found in the table.
| Rafter length, mm | Rafter pitch, mm | Rafter section, mm |
| Up to 3000 | 1200 | 80x100 |
| Up to 3000 | 1800 | 90x100 |
| Up to 4000 | 1000 | 80x160 |
| Up to 4000 | 1400 | 80x180 |
| Up to 4000 | 1800 | 90x180 |
| Up to 6000 | 1000 | 80x200 |
| Up to 6000 | 1400 | 100x200 |
S4– Overhang from the side of the gables. Optimal value S4 approximately 500 mm.
O1 And O2- this is the width and thickness of the sheathing boards of your future attic roof.
R– The gap between the sheathing boards (sheathing pitch).
Section (width O1 and thickness O2) roof sheathing depends on the weight and rigidity of the roofing material, as well as the angle of inclination of the roof. The sheathing should provide sufficient support, but at the same time not weigh down the structure. Determine approximate width values ( O1), thickness ( O2) boards for sheathing and step ( R) is possible using table data.
L1 And L2– The length and, accordingly, the width of the sheet of roofing material depends on its type and production features. Pay attention to the compliance of the parameters declared by the manufacturer with regulatory documents (for example, GOST 30340-95 for slate, GOST R 56688-2015 for ceramic tiles, GOST 24045-2010 for corrugated sheets).
Approximate length and width values different materials, used for the roof of an attic roof, are given in the table.
| Type of roofing material | Height L1, mm | Width L2, mm |
| Corrugated sheet | 1000-1400 | 800-1200 |
| Slate (GOST 30340-95) | 1750 | 980, 1125, 1130 |
| Ceramic tiles | 310, 333, 347 | 190,190, 208 |
| Bituminous shingles | 1000 | 317 |
| Metal tiles | 1120, 1180 | 1040, 1100 |
| Ruberoid | 1000 | 750, 1005, 1025 |
| Euroslate (Ondulin) | 2000 | 950 |
| Galvanized steel | 720-1800 | 2000, 2500 |
| Roofing iron | 510-1000 | 710-2000 |
L3– Overlap of the roofing sheet in percentage. The value of the overlap depends on the type of roofing material, the angle of inclination of the roof and is regulated by SP 17.13330.2011 “Roofs” (Updated edition of SNiP II-26-76). The required overlap of roofing material is often indicated by the manufacturer on the packaging.
The calculator allows you to calculate the dimensions of a sloping roof: the length and width of the roof sheet for each slope and the roof area. The required length and number of rafters and sheathing for the construction of an attic roof. Volume of lumber for making rafters and sheathing. Number of rows of sheathing boards. Calculate the amount of roofing and under-roof insulating material (calculated taking into account a 10% overlap for tight installation) of the attic roof of the house. The use of an under-roof lining (the so-called vapor barrier) is extremely important for blocking the penetration of vapors from residential premises and preventing the formation of condensation, which will extend the life of the insulation and roofing material. Having such data, you can easily assess the feasibility of building a mansard roof and more accurately determine the volume the required material. Please note than better materials for rafters, sheathing you can order, the lower your costs for the attic will be. It is also imperative to consult a qualified roofer. Because a mistake made at the design stage is much easier and cheaper to correct.
Features of many architectural projects private households often become more attractive and interesting thanks to the inclusion of a device in the project attic floors. Such an idea as using the space under the roof as a living space, in addition to architectural and design attractiveness, also contains a number of problematic issues, such as the correct calculation and installation of the roof.
Features of the attic roof
In view of this, the attic is a specific building structure adapted for normal living, that is, a full-fledged living space, then the roof of such a building has its own characteristics:
- special form of roof roof structure;
- installation of a full-fledged thermal insulation coating, ensuring a comfortable stay inside;
- the presence of a large number of window structures in the roof;
- installation of internal communications in the attic.
Features of the roof truss system
The most important element of the attic in all respects is rafter system roofs. The correct execution of this element of the building structure allows not only to implement a solution regarding the installation of an attic, but also to ensure the correct operation of the entire building.
As practice shows, today it is possible to construct an attic space almost for any type of roofing structure. Depending on the design of the building, the attic can be successfully equipped with either a pitched roof, a gable roof, a hip roof or a multi-gable roof.
However, the most acceptable is attic roof option, the main difference of which is availability of increased space under the roof by changing the angle of the slope.
This solution is most justified from an architectural point of view, but at the same time it more expensive in terms of materials and somewhat more technically complex than conventional gable roof.
- side hurries;
- ridge rafters;
- sheathing of side rafters;
- sheathing of ridge rafters;
- racks;
- struts;
There are two types of rafters - layered and hanging. The first ones are used where there is an intermediate in the project bearing wall. Simply put, one side of the rafter rests against the mauerlat along the outer wall, and the other against the inner wall.
Hanging rafters have two tiers: the lower one - side rafters and the upper one - ridge rafters. To create rigidity in the structure of hanging rafters, as a rule, lintels and racks are installed.
Where to start building an attic roof?
Construction of the attic floor, as a rule, occurs as a stage of construction of the building as a whole, however, if the attic floor is equipped from an old building or is rebuilt during the reconstruction of the roof, then the construction plan is developed taking into account existing features building.
As a rule, for proper organization construction work A plan and working drawing are developed, according to which the necessary materials are calculated and the stages of construction are worked out.
Rules for calculating the attic floor
When constructing a construction plan and working drawing, the basic rules for the calculation sequence are used:
- choosing a roof truss system design;
- calculation of the attic space;
- calculation of load and quantity of materials;
- work plan.
Wherein main role the correct calculation of indicators plays a role.
Calculation of indicators
When calculating the plan the attic floor and subsequent construction plays a huge role right choice calculations of indicators.
The initial step in calculating attic indicators is to calculate the usable area of the attic.
Optimal is the minimum consideration of the following indicators: The height of the attic ceiling is 2 meters, the width is 3 meters. Such parameters are considered necessary for a comfortable stay in the room. In addition, the blind area of the attic floor is determined.
The basic rule for calculating the usable area is to take into account the distance from the floor to the ceiling bend of 90 centimeters or more.
The remaining area of the attic is a blind area, the use of which as a living space is irrational.
The roof area is calculated by calculating the area of each individual element roof slopes. That is, if the roof has two slopes with one kink, then the area of each element is calculated separately, first the side slope, after the ridge slope, the resulting values are summed and multiplied by 2.
The following from the calculations of indicators is the calculation of the truss structure:
- calculation of the angle of inclination of the side rafters;
- calculation of the angle of inclination of ridge rafters;
- calculation of the amount of materials for rafters;
- lathing calculation;
- calculation of roofing material.
Angle of inclination of side rafters
Calculation of the angle of inclination of the side rafters is carried out mainly in three ways:
- Geometric, the simplest and reliable way, the Pythagorean theorem known from school is used.
- Reference, this method allows you to determine the angle of inclination of the rafters using a special reference table;
- Method of geometric constructions– a method in which a large-scale construction of a plan for the rafter system is carried out, followed by the calculation of the necessary parameters;
- Using a construction calculator – this method good for Internet users, many construction sites offer online calculators for calculating various parameters.
Angle of inclination of ridge rafters
Considering that the ridge rafters are somewhat smaller than the side rafters, and that the structure of the ridge rafters is usually supported by posts, the inclination angle is chosen to be 30 degrees.
Roof surface area
For ease of calculation roof surface the entire surface is divided into simple geometric figures– rectangles and triangles. The area of each section is calculated separately and the values found are then summed up.
Eg, broken line gable roof divided into four sections - two lower side and two upper ridge sections. Find the area of the side and ridge sections of the roof, and then multiply by 2.
Attic floor area
Most often the attic floor determined by the area of the attic space. In this case, the line of the walls is determined and the area of the room is directly calculated. When the attic walls run along the line of the racks, the length of the building is multiplied by the distance between the opposite racks.
In case the room will have a ceiling bend (a roofing structure will be used as part of the ceiling), the area of the attic floor is calculated by finding the area of the attic surface figure limited by the conditional line of the ceiling bend line along the floor surface at a height of 90 centimeters.
Approximate weight of roofing material
When making roof calculations, you should keep in mind that the weight of the roofing material must be taken into account in the calculations.
So, it should be taken into account that 1 square meter may have mass:
- slate – 11 – 13 kg;
- soft tiles – 9 – 15 kg;
- galvanized sheet – 3 – 6.5 kg;
- ceramic tiles– 50 – 60 kg;
- metal tiles – 5 – 6kg;
Number of rolls of overlapping insulation material
When calculating the insulating material You should know that the overlap of the coating strips should be 10 centimeters.
The standard size of many manufacturers of rolled insulation materials is 10 or 15 meters long and 100 centimeters wide.
However, when choosing a specific manufacturer and a specific material, it is useful to find out the actual dimensions of the roll. It's no secret that different manufacturers can be used technical specifications and product parameters.
Loads on the side/ridge rafter system
Calculating loads on the side and ridge parts of the roof, should be taken into account when calculating the average load of 200 kg per linear meter.
This load can easily withstand snow and wind loads. roofing system.
Making snow calculations and wind load on the roof is carried out using special reference books and tables, which indicate the coefficients of snow and wind load.
So, for example, in different regions the snow load can reach 220 kilograms per square meter.
When calculating a specific roof, you should know that there are correction load factors depending on the angle of the roof:
Thus, when calculating the snow load on the roof with an average regional snow load of 220 kilograms and a ridge roof angle of 30 degrees, it is equal to:
220 * 1.25 = 275 kilograms per square meter.
Calculation of lengths and other sizes mansard roof when constructing a drawing occurs according to formulas known from the mathematics course high school. For convenience of calculations, the cross section of the roof is presented as several simple figures: the attic space between the support posts, the floor beam and the tie is represented as a rectangle.
Side rafter space a section of the floor beam to the mauerlat and a support post - a right triangle. The ridge rafters and the tie form an isosceles triangle. Now, even without extraordinary abilities, you can calculate the main lengths of the rafters.
Side rafter length
Considering that the side rafters represent a hypotenuse right triangle, the height of the support before tightening is 2.5 meters, and the angle of inclination of the rafters is 60 degrees, It’s easy to calculate the length of the rafter leg:
- Rafter leg length = 0.5 + support height / cos 60 = 0.5+ 2.5/ 0.5 = 5.5 meters
Where 0.5 is the length of the roof eaves, it must be taken into account, since the removal of the roof from the wall of the house must be mandatory.
Ridge rafter length
The length of the ridge rafters is calculated using the calculation formula for equilateral triangles where:
- V– the base of the triangle and is equal to the length of the puff, that is, as in in this example 4 meters;
- angle a, at the base of the triangle is equal to the angle of inclination of the ridge rafters, that is, 30 degrees;
- apex angle triangle is 120 degrees.
Finding the length of the ridge rafters is done using the formula:
Rafter length = Tie length/2cos a
Rafter length = 4 meters/2x0.866
The length of the ridge rafters is 2.3 meters
Number of side and ridge rafters
Depending on the linear dimensions of the building and the roof area, it is planned to install side and ridge rafters at equal distances. It is considered normal to install standard rafters 50x100 mm every 0.7 - 0.8 meters with a rafter leg length of 6 meters and 1.2 meters with a leg length of 3 meters.
Minimum cross-section of side/ridge rafters. Weight and volume of timber for rafters
When calculating the roof structure, the following minimum rafter sections are taken into account:
- side rafters and ridge rafters - 50x100 millimeters.
When calculating weight, the average density of wood at a humidity of 18% is taken - 500 kilograms per cubic meter.
Number of side/ridge rows of sheathing
When calculating the sheathing, depending on the selected roofing material, the type is taken into account required sheathing system:
- for soft roofing materials a continuous sheathing made of plywood or OSB board is installed;
- for semi-rigid roofing materials a sparse or compacted sheathing is installed;
- for rigid large-size roofing materials such as slate, a sparse sheathing is arranged;
- for large semi-rigid roofing materials (roofing iron) a continuous sheathing is arranged.
When calculating the number of rows of sheathing, it is recommended to adhere to the following rules:
- when calculating the sheathing For roofs with a slight slope of up to 12 degrees, continuous sheathing is recommended;
- for roofs with a slope of up to 60 degrees, it is recommended to install lathing in increments of 20 - 23 centimeters;
- for roofs with a large slope more than 60, it is recommended to install the lathing in increments of 60 centimeters.
It is considered normal to install lathing from edged boards 20 cm wide every 20 - 30 cm
Total number of rows of sheathing
Based on the fact that the lathing is used for edged board 20x2 centimeters and the distance between the rows of sheathing is taken to be 20 centimeters, for every meter of roofing there are 3 rows of sheathing.
By increasing the distance between the rows of sheathing to 30 centimeters, there will be 2 rows of sheathing for every meter of roofing.
When calculating the number of rows of sheathing, 2 more rows are added to the total number of rows - ridge and cornice.
Uniform distance between side/ridge sheathing boards
Uniform device The distance between the side ridge boards of the sheathing is necessary not only to achieve the required structural strength, since such a structure must withstand not only the weight of the roof, but also withstand snow and wind loads.
In addition, the uniform distribution of the sheathing allows for better installation of the thermal insulation cake.
Number of sheathing boards of standard length
According to the assortment of lumber, the industry produces standard sizes of lumber from softwood and hardwood.
The standard lengths of lumber are:
- softwood lumber 4.5 meters and 6 meters long;
- hardwood lumber – no more than 5 meters;
- softwood lumber for special needs 9 meters.
Thus, for one row of house sheathing 8x10 meters long, 2 boards of 6 meters each are needed for a roof slope of 10 meters (it should be taken into account that the roof protrudes onto the gable by at least 20 centimeters on each side).
Volume of sheathing boards
To calculate the volume of a lumber order in cubic meters you need to:
- count the number of boards, necessary for lathing, taking into account scraps;
- translate linear dimensions boards from centimeters to meters (a 20x150 mm board 6 meters long when converted will be 0.02 (board thickness) x 0.15 (board width) x 6 (length));
- multiply the number of boards by the dimensions of one board in meters, the result is the volume in cubic meters ( 0.02x0.15x6x20= 0.36 cubic meters)
Approximate weight of sheathing boards
Taking into account objective properties of wood, coniferous wood is usually used for lathing.
However, you should know that when using freshly sawn wood, only changes in the wood itself are possible - warping, cracking, torsion, but also the occurrence of rotting of wood fibers, the appearance of fungus and mold.
Therefore, when installing sheathing, and especially roof sheathing mansard type use dry wood.
When calculating weight wooden sheathing The basis is the weight of wood at a moisture content of 18%, which on average is:
- Norway spruce wood – 450 kg;
- Scots pine – 510 kg;
- cedar pine – 440 kg;
- Siberian fir – 380 kg;
- Caucasian fir – 440 kg.
When calculating the weight of rafters and sheathing, an average weight of lumber of 500 kg per cubic meter is taken.
Thus, if 20 boards of 20x150 6 meters each are needed for the sheathing, which is 0.36 cubic meters of spruce, then the weight of such a structure will be equal to:
0.36x450=162 kg
Getting started When calculating the roof structure of a mansard roof, it is necessary to draw up a roof plan, and in this case, you need to draw up on paper the most detailed plan, taking into account the scale.
On paper with a pencil, ruler and protractor calculate possible options rafter system devices. Since changes at the construction stage most often have to be made in the direction of increasing the amount of materials.
Construction Materials
During the construction of an attic roof Special attention pay attention in calculations correct selection materials, since incorrect selection and installation of building materials can lead to errors in the installation of the roof and its weighting of the structure.
Material parameters for the construction of an attic roof
For the installation of rafters construction, bars of various sections are calculated, from coniferous wood, when choosing a material and inspecting it, attention is paid to the presence of knots and their quantity; the presence of no more than 3 knots per 1 linear meter of material is considered normal.
For lathing installation The standard board length of 4.5 or 6 meters is taken into account.
When calculating the roofing The standard dimensions of roofing materials are taken as a basis, and if the side rafters have a length of 2.5 sheets of slate, then 3 rows are taken into account, that is, it is rounded up.
What section of rafters are required?
When constructing an attic roof, the calculations take the standard dimensions of the bars for installing rafters - 50x100 millimeters or 50x150 millimeters.
Wind load calculation
is the temporary load on the roof plane. The wind load is calculated in accordance with this, this is the good old Soviet SNiP, however, today it is not valid in all regions of Russia; many subjects have developed their own regional standards.Carrying out calculations wind load of the roof is associated with setting the required safety margin for short-term exposure to strong gusts of wind. This need is due to the fact that the wind load has significant differences even in the same area.
In total, wind strength is mainly influenced by:
- region of location of the building;
- presence of urban development;
- the height of the building and the angle of the roof.
Snow load calculation
Unlike wind load snow load is longer lasting and belongs to the category of long-term loads. Several factors influence the determination of the snow load - the slope of the roof, the number of roof slopes, the presence of chimneys, roof drops, parapets and dormer windows.
Besides, important role plays an approximate amount of snow cover, depending on the location.
, the snow load is calculated according to SNiP 2.01.07-85 “Loads and impacts”, and a correction factor is taken depending on the angle of inclination of the roof:- the coefficient for tilting up to 25 degrees is 1.
- the coefficient for a roof slope from 25 to 60 degrees is 1.025;
- at an angle of inclination greater than 60 degrees, the coefficient is not taken into account.
Calculation of a sloping mansard roof
The calculation of a sloping mansard roof is carried out in stages, taking into account the main parameters in which the following are calculated:
- corner roof slope;
- length and the cross-section of the ridge and side rafters, their reinforcement;
- section and sheathing pitch;
- square side and ridge slopes;
- weight roofing material, calculation of loads and weight of insulation;
- calculation distances between rafters.
At the end of the calculation, a calculation is made required material.
Calculation of a gable mansard roof
Calculation gable roof practically no different from the calculation of a sloping roof, except that the calculation does not include the calculation of ridge and side rafters, side and ridge slopes of the roof.
Main errors in calculating attic roofs
When calculating attic roofs, the following mistakes are often made:
- incorrectly calculated angle of inclination and length of rafters;
- errors are allowed in calculating the snow load, correction factors for the roof slope angle are not taken into account;
- ventilation is not taken into account gap when installing a heat-insulating cake;
- device features are often neglected roofs from various materials, as a result of which it is produced incorrect installation and further operation of the roof.
Use the online mansard roof calculator to calculate required quantity materials for this type of roofing. Accurate calculation of the sheathing, the angle of inclination of the rafter system, and the load on the roof of the house.
Specify roofing material:
Select a material from the list -- Slate (corrugated asbestos cement sheets): Medium profile (11 kg/m2) Slate (corrugated asbestos cement sheets): Reinforced profile (13 kg/m2) Corrugated cellulose-bitumen sheets (6 kg/m2) Bitumen (soft , flexible) tiles (15 kg/m2) Galvanized sheet metal (6.5 kg/m2) Sheet steel (8 kg/m2) Ceramic tiles (50 kg/m2) Cement-sand tiles (70 kg/m2) Metal tiles, corrugated sheets (5 kg/m2) Keramoplast (5.5 kg/m2) Seam roofing (6 kg/m2) Polymer-sand tiles (25 kg/m2) Ondulin (Euro slate) (4 kg/m2) Composite tiles(7 kg/m2) Natural slate (40 kg/m2) Specify the weight of 1 square meter of coating (? kg/m2)
kg/m2
Enter roof parameters:
Laying width A1 (cm)
Laying width A2 (cm)
Base length D (cm)
Lifting height B1 (cm)
Lifting height B2 (cm)
Length of side overhangs C (cm)
Front and rear overhang length E (cm)
Rafters:
Rafter pitch (cm)
Type of wood for rafters (cm)
Working area of the side rafter (optional) (cm)
Lathing calculation:
Sheathing board width (cm)
Sheathing board thickness (cm)
Distance between sheathing boards
(cm)
Snow load calculation:
Select your region using the map below
1 (80/56 kg/m2) 2 (120/84 kg/m2) 3 (180/126 kg/m2) 4 (240/168 kg/m2) 5 (320/224 kg/m2) 6 (400/280 kg/m2) 7 (480/336 kg/m2) 8 (560/392 kg/m2)
Wind load calculation:
Ia I II III IV V VI VII
Height to the ridge of the building
5 m from 5 m to 10 m from 10 m
Terrain type
Open area Closed area Urban areas
Calculation results
Angle of inclination of side rafters: 0 degrees.
Angle of inclination of ridge rafters: 0 degrees.
The angle of inclination is suitable for this material.
It is advisable to increase the angle of inclination for this material!
It is advisable to reduce the angle of inclination for this material!
Roof surface area: 0 m2.
Attic floor area: 0 m2.
Approximate weight of roofing material: 0 kg.
Number of rolls of insulating material with 10% overlap (1×15 m): 0 rolls.
Rafters:
Load on the side rafter system: 0 kg/m2.
Load on the ridge rafter system: 0 kg/m2.
Side rafter length: 0 cm
Ridge rafter length: 0 cm
Number of side rafters: 0 pcs.
Reduce the pitch of the rafters!
Number of ridge rafters: 0 pcs.
Reduce the pitch of the rafters!
Lathing:
Number of side rows of sheathing (for the entire roof): 0 rows.
Number of ridge rows of sheathing (for the entire roof): 0 rows.
Total number of rows of sheathing: 0 rows.
Uniform distance between the side sheathing boards: 0 cm
Uniform distance between the ridge boards of the sheathing: 0 cm
Number of sheathing boards with a standard length of 6 meters: 0 pcs.
Volume of sheathing boards: 0 m3.
Approximate weight of sheathing boards: 0 kg.
About the calculator
The online attic roof calculator will help you calculate the angles of inclination of the side and ridge slopes, the number and required cross-section of rafters, the volume of sheathing and other materials for roof construction. You won't have to do extra calculations because this calculator includes most existing roofing materials, such as bitumen shingles, cement-sand and ceramic tiles, metal tiles, bitumen and asbestos-cement slate, ondulin. If you use non-standard material, or want to get more accurate calculations, you can specify the weight of your own roofing material by selecting the appropriate item in the drop-down list of materials.
Before designing an attic floor, read SNiP 2.08.01-89 “RESIDENTIAL BUILDINGS” seriously.
Note!
The calculator makes calculations in accordance with the current SNiP “Loads and Impacts” and TKP 45-5.05-146-2009.
The design of a mansard (broken, sloping) roof is different in that on each side it contains two slopes with different angles inclination: steep side and sloping hanging. Thus, under the roof a comfortable space, which can be used as a living space. This room is called the attic floor or simply the attic.
Attics were first built in the 17th century. An attic can be erected relatively easily, both during the initial construction of a building and as an addition to an existing building. Thus, it provides an alternative in the construction of an additional floor.
Since the side slopes are very steep, you should carefully choose building materials. It is possible that an attic roof will require additional costs. This is especially important for residential attic premises: They will need larger gable windows and better insulation.
When filling out the fields of the calculator, read the additional information located under the sign.
If you have any questions or ideas regarding this calculator, you can write to us using the comment form at the bottom of the page. We'd love to hear your opinion.
Additional information about the calculation results
Angle of inclination of side rafters
The angle at which the side rafters are inclined to the plane of the ceiling. He's usually cooler. Different roofing materials allow different maximum angles. The calculator will show whether it is possible to build a roof at a given angle using the selected roofing material.
Angle of inclination of ridge rafters
The angle at which the ridge (hanging) rafters are inclined to the plane of the attic floor. This angle is usually more sloping. Different roofing materials allow different maximum angles. The calculator will show whether it is possible to build a roof at a specified angle using the selected roofing material.
Roof surface area
The area of the entire roof surface including overhangs. To determine the area of one slope, it is enough to divide the indicated value by two.
Attic floor area
The area of the attic premises. This does not include the area under the side slopes.
Approximate weight of roofing material
The weight of the selected roofing material for the entire roof area, taking into account overhangs.
Number of rolls of insulation material
The required amount of insulation material for the entire roof area. The quantity indicated in rolls is based on standard size roll - 15 meters long, 1 meter wide. The calculation also took into account an overlap of 10% at the joints.
Loads on the side and ridge rafter system
These values show the maximum possible loads on a given roof. The calculations involve both the total mass of the roofing pie and the sum of the wind and snow loads of the selected region.
Side rafter length
The estimated length of the rafters of the side slopes, located from the bottom of the slope to the top of the attic floor.
Ridge rafter length
The estimated length of the ridge (hanging) rafters, located from the top of the attic floor to the roof ridge.
Number of side and ridge rafters
The total number of side and ridge rafters required to construct a roof with the given parameters.
Minimum section of rafters / Weight of rafters / Volume of beams
- The first column indicates the permissible cross-sections of rafters in accordance with GOST 24454-80 Softwood lumber. Weight, specified design parameters, and possible roof loads are taken into account. The calculator calculates the total loads that can affect the structure and selects optimal options rafter sections.
- The second column contains information about the weight of rafters with the specified cross-section. Specified here total weight rafters for the calculated roof.
- The third column displays the total volume of rafters in cubic meters. Use these values to calculate the cost of lumber.
Number of rows of sheathing
The number of rows of sheathing that will be needed for the entire roof with the given parameters.
Uniform distance between sheathing boards
Number, volume and weight of sheathing boards
The total number of boards for arranging the roof sheathing, their volume in cubic meters and their total weight.
The main reason for the fairly widespread use of sloping roofs is that a conventional gable roof forms relatively little free space, which in most cases is not enough for use as a living space. At the same time, when erecting a sloping roof during the construction of a private house, it is possible to construct a full-fledged attic. At the same time, we should not forget that a sloping roof looks extremely attractive, giving residential building aesthetic and solid appearance.
Features of a sloping roof
The design of a sloping roof is a variation of the usual gable roof, with a small addition - there is a break on each slope. This essentially turns the roof into a hipped roof. The main purpose of such a change is to increase the under-roof space. Usually there is an attic, which is almost a full-fledged residential floor.
The construction of a sloping roof is somewhat more complicated than a regular gable roof, but is not very different from the construction of a hip roof. Basic design feature The roof in question is the presence of two types of rafters:
- Bottom (layered). In most cases they have a large angle, the value of which is equal to or greater than 60 degrees;
- Upper (hanging). The angle of their location is sharper, usually it does not differ much from 30 degrees.
Sloping roofs are most often used in private housing construction. Therefore, its width rarely exceeds 5-6 meters. This is explained much more complex design rafter system with a larger width, which complicates the work, increases its cost, making this design solution economically infeasible.
It should also be taken into account that the structure of a broken roof contains not only rafters, but some additional and auxiliary elements in the form of racks, struts, tie-downs, etc. Their dimensions are determined when calculating the rafter system. It is precisely because of their presence that the rafter system is somewhat more complex than that used with a gable structure.
We should not forget that an important advantage of a sloping roof is that it gives the appearance of the building a certain solidity, and simply looks much more attractive than a regular gable roof. It is precisely this combination of high functionality of the building, expressed in the possibility of equipping an attic, and extremely attractive and aesthetic appearance, largely explains the reason for the popularity of the design in question, despite its relative complexity.
Calculation of roof dimensions
The calculation of the size of a sloping roof can be conditionally divided into two parts.
Calculation of roof covering area
This part is the simplest and most uncomplicated. To calculate the area, simply make a plan of it with all the dimensions. In this case, the diagram will be a set of simple figures - in most cases quadrilaterals, in particularly complex ones constructive solutions- and triangles. Calculating the areas of these figures is not difficult, just like adding them to get total area coverings.
But even these procedures can be performed using numerous calculators, which greatly facilitate the second part of the calculations.
Calculation of the dimensions of elements and parts of the rafter system
Calculating the dimensions of a rafter system for a sloping roof is much more difficult, including due to the fact that it contains many connecting rather complex units. But without them correct calculation and implementation is impossible for a long time and reliable operation roofs. The dimensions of the rafter system are influenced by many factors:
- weight of roofing pie components:
- battens and counter-battens;
- completed waterproofing and vapor barrier;
- thermal insulation material;
- the direct weight of the roof covering;
- geometric dimensions main roof elements:
- the size of the span from the overhang of the eaves to the ridge of the roof;
- the angle of the upper and lower rafters;
- selected pitch of sheathing and rafters;
- operational loads (weight of people repairing and maintaining the roof, engineering and maintenance devices, fences, aerators, skylights etc.)
Based on the list of factors listed above that influence the size of the required rafter system, it becomes clear that its calculation is not a simple operation. That's why it was developed a large number of auxiliary online calculators, with the help of which it is quite easy to perform all the calculations.
Calculators will do an excellent job of calculating the total area of the roofing covering, as well as the required amount of material for hydro- and vapor barrier.
To calculate the rafter system, you must enter the appropriate data into the calculator, which should characterize each of the above influencing factors.
The approximate wind load is easily determined from the corresponding map for each region.
The resulting wind load value must be adjusted depending on the coefficient, which takes into account the height of the building being constructed and the type of area where the construction site is located.
The amount of snow load that can affect the roof is taken from the corresponding map containing relevant data for the regions of Russia.
Based on the area determined on the map, you can find out the amount of snow load required for calculation.
Most calculators independently calculate this parameter; it is enough to simply indicate the materials used and the main geometric dimensions of the designed roof, namely: the pitch of the rafters and sheathing, the angles of the slopes, the distance from the ridge to the overhang, as well as the material of the roof covering. The program will perform all other calculations offline.
After introducing all necessary information, the calculator will give all the necessary dimensions of the elements and parts of the rafter system, as well as the roofing area and the necessary vapor and waterproofing materials.