Determine the roof load : general principles

method of calculating load on the roof

basic rules, methods of calculating the pressure on the roof of the house is based on clear standards of construction - SNIP 2.01.07-85 titled "Loads and effects" (changes made in 2008).This is not the only source that contains the official data for the calculation of the pressure on the roof of the house.

initially is to determine what are the sources of the roof load:

• Snow mass;
• gusts of wind;
• Weight load of roofing materials;
• weight crates;
• layer of insulating material;
• rafter boards.

detailed calculation of the natural load of

snow load from the snow can be calculated by the formula:
S = μ • Sg.
components of the formula:

• S - the final figure of the snow pressure.It is measured in kilograms per square meter.
• μ - measure the slope of the roof - alpha, measured in degrees.
• Sg - standard snow load.

slope of the roof is determined by dividing the height H of half the span L. final figure can be seen from the table:

Table 1: Calculation of the roof structure inclination
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 °

load Calculation with wind gust

Strong winds adversely affect the roof structure with a steep slope (angle greater than 30 degrees).

Building Standards section on improvement of the roof, said about the formula for calculating wind loads of roofing:
Wm = Wo • K • C.Details
formula:

• Wo - measure wind load.
• K - coefficient of wind pressure changes.

results need to look at below given data:

load index 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 changes to look at the table:

coefficient K
height	Open terrain	Closed terrain, obstructions greater than 10 m	areas with tall buildings over 20 m
to 5m	0,75	0,5	0,4
from 5 to 10m	1,0	0,65	0,4
from 10 to 20m	1,25	0,85	0,53

Building standard SNIP 2.01.07-85 "loads and effects" a more detailed description of the roof load.In it you can read about all the sources and loads calculations.

To get acquainted with the problems of load on the roof can be viewing the video in the next tab: