When calculating materials for cross roof it is better to use the drawing of the plan of the house. In the subsequent it will be possible to apply general lay-out of rafter system on it. When determining amount of materials the house sizes, expected loads of roof are considered.

One of the most difficult roofs is cross. Thanks to its mnogoskatnost and big bias the atmospheric precipitation easily descends from surface. Also the special system of rafters is used that gives the chance to accept to roof heavy loads. Such options differ in durability and durability. They can be met on baths, residential buildings, dachas.

## Basic elements of design

Before making calculations, it is necessary to learn about the basic structural components:

- Inferior purlin. The basic bar with section 10*10 or 15*10 see is mounted on all perimeter of the house.
- Rafter system. Is made of boards. Its size depends on bias of roof and total area. Section is chosen taking into account heater thickness.
- It is necessary for uniform load dispatch. Calculations depend on whether there will be it continuous or with certain step.
- Is made of bar, the roof is placed on the most upper part.
- Valley gutter. It is formed in position of joints of two slopes. Under such internal corners the continuous furring surely becomes.
- Roof overhang. Allows to protect walls and the base from precipitation.
- Drains and snegozaderzhatel. Their installation is optional, but with their help it is possible to prolong life cycle of roof and to ensure additional safety.

## Calculation of inferior purlin

This part is support for other design. Its sizes depend on perimeter and the area of the house, material of rafter system and roof, weather conditions. Thickness of inferior purlin should not be less than 10 cm, and the space from edge of external edge of wall - is not less than 6 cm. When using waterproofing material the distance has to be from 40 cm.

At first length and perimeter of inferior purlin is measured. The weight of wooden bar is recognized by the obtained data. The formula is for this purpose applied: m=rV, where r – wood density, V – the volume of inferior purlin, m – the mass of wooden bar. Volume is calculated by V=SL formula where S – bar section, L – its length.

## Calculation of materials of rafter system

This part is responsible for rigidity, evenly distributes loading. For calculation all factors influencing design are considered. They are variable, regular and atypical. All calculations are described in Construction Norms and Regulations therefore when performing determination of exact parameters the document is recommended to be held near itself.

For definition of snow load the formula S=Sg*µ is used (Sg – snow weight on 1 m² of the area, µ — coefficient of dependence on tilt angle). If the roof has bias less than 25 degrees, then the coefficient will make 1.0. This parameter at bias from 25 to 60 degrees – 0.7. If slopes very big, then the snow load can not pay off as snow will not be able to keep.

At identification of wind load the formula W=Wₒ*k is applied (W ₒ - standard value, defined depending on the wind area (it is specified in Construction Norms and Regulations), and k is the coefficient revealing dependence of wind force on height of the house and its location).

When choosing rafter system also the weight of all materials which will be used is considered. It is roof, waterproofing, the equipment, vent system. The draft flooring usually weighs from 18 to 20 kg/sq.m, furring – 8-10 kg/sq.m. All rafter system gives loading from 15 to 20 kg/sq.m.

At identification of final loading all listed loadings are summarized. At the same time calculation comes down to definition of indicator on each leg separately and to calculation of section of separate element. For distributed load it is necessary to increase distance between rafters by one running meter and total load which affects one square meter of roof.

It is necessary to remember that because of difficult rafter part the consumption of material will be essential. Same concerns also roof.

## Roof material calculation

Its production of furring will require boards not less than 3 cm thick, bar with section 5 on 5 cm.

The cross roof is often formed two dual-slop. Therefore for calculations it is possible to use formula which is suitable for the last, but the received indicator should be increased twice.

Is defined:

- type of roof;
- tilt angle;
- complexity degree.

For calculation of total area this parameter on one slope is learned. As this element of form the calculation formula standard has the rectangle form. At the same time width of slope is considered from the fad to edge of eaves, and length – from speakers for pediments of edges. If the roof has difficult design, then at first separate it into several correct figures. Their areas pay off separately, then develop.

The metal tile is popular. Standard width of leaf is about 1.1 m. Therefore the number of sheets depends on width of slope. There are also such indicators as:

- length of sheet of material;
- length of overhangs;
- length of slope;

The received number is rounded to whole.

If it is about slate, then when calculating it is necessary to consider that during laying the area of each element decreases. It is connected with the fact that sheets keep within with an overlap. It is the simplest to make calculation of quantity of soft tile. For this purpose the total area of roof, length of eaves and skates is defined. For example, at the area of 280 sq.m it will be necessary to buy 87 packs of material.

In conclusion we will note: the cross roof - is difficult in design as crossing of slopes is observed. It is the best of all to use special calculators. It is enough to enter the necessary parameters in advance to decide on the sizes and to learn amount of necessary materials.