Calculation of the snow load on the roof - calculations and
As is known, Russia is famous for cold, long winters with heavy snowfalls. On the one hand, this is a great opportunity to enjoy fun snow fun, and on the other - a problem for every owner of a private house. Snow load is the most important indicator of roof construction, the calculation of which is carried out in the process of project creation. Calculating the exact weight of the snow, which the roof system must withstand, helps to make a certain margin of safety, ensuring that the roof is not deformed during snowfall. In this article we will describe how the snow load is calculated for a specific construction region and roof configuration.
What is snow load?
The calculation of the snow load is a necessary calculation performed to create a reliable, durable roof that will withstand the increase in load during snowfall. From this indicator depends on the number and thickness of the cross section of the truss frame and in general affects the choice of roof structure. The amount of snow load has an effect:
- The region in which the construction is underway. The most snowy are mountainous areas, where a few meters of precipitation can fall within 24 hours.
- Roof slope. The greater the slope angle of the slopes, the more snow slides off the roof, respectively, the lower the snow load. With a slope of over 60 degrees, almost all the snow immediately leaves the surface of the slope, so the snow load equals zero.
- Snow weight On average, 1 cubic meter of snow weighs 100 kg, but the wet snow mass and frost weighs significantly more - up to 300 kg / m3.
Consider that according to the construction climatology, the territory of Russia is divided into 8 zones in terms of the amount of snow falling. This annual average standard value is used in calculations of the carrying capacity of the truss frame.
What does this indicator affect?
It seems to the man in the street that snow weighs very little and does not exert strong pressure on the roof surface. However, a snow cap that accumulates without regular clearing may increase the load on the frame by 100-300 kg / m2. Of course, part of the snow leaves the roof naturally, blown away by the snow, but the remaining 95% of the mass remains on the slope, which is why the following processes occur:
- In winters, when thaws alternate with sharp frosts, snow on the roof surface partially transforms into ice, partially gets wet, as a result of which the snow cap weight increases by 2-3 times, and it becomes impossible to clean it without spoiling the roof covering.
- If you choose a complex roof, which has several associated slopes, keep in mind that snow accumulates more actively in places of junction, valley and other architectural elements, because of which the snow load is unevenly distributed.
- Snow spontaneously sliding from the ridge of the roof to the roof overhang represents a serious danger to human health, therefore, I will equip the roof with snow guards. In turn, the delay of snow on the eaves increases the load on the ends of the rafter legs.
- Unorganized descent of snow leads to the disruption of elements of the drainage system.
Note! Calculating the weight of the snow that the roof has to withstand during snowfall helps to create a durable, solid construction that cuts out more than one winter without the threat of collapse.
Computation technology
It is rather simple to perform the calculation of snow load, however, this step must be performed in order to design a reliable and durable roof, to determine the composition and size of the cross section of the truss frame elements. The calculation is performed according to the following scheme:
- First, according to the climate maps, it is determined in which zone the area in which the house is built is located.
- Then, according to reference books, the value of the normative average annual snow load is determined.
- Perform a calculation of the total snow load by multiplying the standard indicator by the coefficient taking into account the angle of inclination of the slopes. With a slope of 25 degrees or less, the coefficient is equal to one, with a slope of 25-60 degrees it takes a value of 0.7, and with a slope of more than 60 degrees it is not taken into account.
Important! The calculation of the snow load on the roof does not take into account the used roofing material, although experienced craftsmen believe that different coatings affect snow accumulation on the roof surface differently. Rough materials (ruberoid, shingles, ondulin) do not allow the snow mass to slide off, and smooth (metal tiles, folded roofing, corrugated flooring) on the contrary prevent accumulation.
Ways to reduce the load
Calculation of snow load is a real way to prevent roof collapse during prolonged snowfall, when it is impossible to relieve snow slopes from snow. Knowing this indicator, you can correctly choose the slope of the structure, develop a project for the truss frame and select the material for its production of sufficient strength. To reduce the load, you can perform the following activities:
- Increase roof pitch. In especially snowy regions, it is recommended to erect a roof with a slope angle of 45-60 degrees, on the surface of which the snow practically does not linger.
- Use smooth roofing materials. To facilitate the slippage of snow masses from the roof surface, apply a coating with a smooth and slippery surface. Metal roofing is ideal for this description.
- Install a system of anti-icing and forced snowmelt. De-icing devices, consisting of heating cables, constantly heat the snow. Melt water leaves the slope through the drainage system to storm sewers.
- Install snow blowers instead of snow barriers. To reduce the load on the lower part of the rafter legs, perform the installation of snow cutters, separating when a layer of snow falls on smaller plates.
Another way to reduce the snow load with insufficient bearing capacity of the roof truss frame is to quickly clear it of snow manually. Of course, this event requires compliance with safety regulations and is performed using safety equipment.
