Method for calculating the roof load
The basic rules, methods for calculating the pressure on the roof of the house are based on clear construction standards - SniP 2.01.07-85 under the title "Loads and effects"( corrections made in 2008).This is not the only source containing official data to calculate the pressure on the roof of the house.
Initially, it is necessary to determine what are the sources of load on the roof:
- Snow masses;
- Gusts of wind;
- Weight load of roofing materials;
- Weight;
- Thermal insulation layer;
- Rails.
Detailed calculation of natural load from snow
The snow load can be calculated using the formula:
S = μ • Sg.
Components of the formula:
- S - the final figure of the snow pressure. Measured in kilograms per square meter.
- μ - roof slope indicator - alpha, measured in degrees.
- Sg - standard snow load.
The roof slope is determined by dividing the height H by half the span L. The final figure can be seen from the table:
| Table 1. Calculation of the roofing structure angle | |
| H / L | Angle Alpha |
| 0.27 | 15 ° |
| 0.36 | 20 ° |
| 0.47 | 25° |
| 0.58 | 30 ° |
| 0.7 | 35 ° |
| 0.84 | 40 ° |
| 1 | 45 ° |
| 1.2 | 50 ° |
| 1.4 | 55 ° |
| 1.73 | 60 ° |
| 2.14 | 65 ° |
Calculation of the load with a gust of wind
A strong wind adversely affects the design of the roof with a steep slope( an angle of more than 30 degrees).
Building standards, the section on roofing, talks about the formula for calculating the wind load of the roof:
Wm = Wo • K • C.
Requisites of the formula:
- Wo - the indicator of the wind load.
- K is the coefficient of wind pressure change.
results necessary to look at below given data:
| Load Indicator wind | ||||||||
| Wind areas | Ia | I | II | III | IV | V | VI | VII |
| Wo, kPa | 0.17 | 0.23 | 0.30 | 0.38 | 0.48 | 0.60 | 0.73 | 0.85 |
| Wo, kg / m² | 17 | 23 | 30 | 38 | 48 | 60 | 73 | 85 |
K - coefficient of wind pressure change see table:
| Coefficient K | |||
| Height | Open area | Closed terrain, obstacles more than 10 m | Areas with a building height of more than 20 m |
| up to 5 m | 0.75 | 0.5 | 0,4 |
| from 5 to 10 m | 1,0 | 0,65 | 0,4 |
| from 10 to 20 m | 1,25 | 0,85 | 0,53 |
Building standard SnI 2.01.07-85 "Loads andimpact "has more detailed descriptions of the loads on the roof. In it you can read about all sources and load calculations.
You can get acquainted with the problems of load on the roof by viewing the video in the next tab:
