The construction of a pitched roof is one of the most popular solutions for garages, outbuildings, sheds and even modern high-tech residential buildings. The key element ensuring the durability of the entire structure is the correctly calculated pitch of the sheathing under the corrugated sheet. Errors at this stage can lead to deformation of the roofing, leaks, and even collapse of the frame under the weight of snow or gusts of wind.
Unlike gable systems, pitched roof experiences uneven loads, and the angle of inclination here plays a critical role in choosing the distance between the elements of the supporting base. Correct sheathing pitch allows the corrugated sheet to withstand the weight of a person during installation and operation, as well as effectively drain water. In this article we will look at the technical nuances that depend on the profile brand and the climatic conditions of your region.
Ignoring building codes can cost you expensive repairs in just a couple of years. For profiled sheets with a thickness of less than 0.5 mm, the sheathing pitch should not exceed 300 mm even with minimal snow loads. Let's take a closer look at how to calculate the optimal distance and avoid fatal installation errors.
Factors influencing the choice of lathing pitch
Determining the distance between beams or boards is not just choosing an arbitrary number, but the result of an engineering calculation. The primary factor is always slope angle. The smaller it is, the more often the support should stand, since the load on the bending of the corrugated sheet increases, and the ability to self-clean from snow and water decreases. On low-slope roofs, water stagnates, increasing the risk of corrosion and leaks.
The second critical parameter is brand of corrugated sheet. Different profiles have different wave heights and metal thicknesses, which directly affects their load-bearing capacity. For example, the wall profile C8 will require much more frequent lathing than the load-bearing H75, which, thanks to its high stiffening ribs, can cover large spans.
We must not forget about the climate map of the region. Snow load in Siberia and the Caucasus is radically different. If there is a lot of snow in your area in winter, you cannot skimp on the number of boards - this will lead to sagging of the metal. The wind load is also taken into account, which on pitched roofs can create a sail effect, trying to tear off the covering.
⚠️ Attention: Never use the lathing step “by eye”. The calculation should be carried out taking into account the minimum thickness of snow cover recorded in your region over the past 50 years.
Dependence of the pitch on the angle of inclination of the roof
The angle of inclination is the main regulator of the frequency of installation of supporting elements. For pitched roofs, this parameter usually varies from 5 to 30 degrees. At small angles of inclination, water flows slowly, and the requirements for tightness and rigidity of the base increase many times over. Required here continuous lathing or the minimum gap between elements.
If the slope angle is from 15 to 30 degrees, you can switch to a sparse installation scheme. In this range, the corrugated sheet already has sufficient rigidity to withstand loads with an increased distance between the boards. However, it is impossible to cross the boundaries of what is permissible without strengthening the metal.
For steep slopes (more than 30 degrees), the snow load becomes minimal, as the snow simply rolls down. In such conditions, the pitch can be increased to the maximum values specified in the technical data sheets of the profile manufacturer. But even here there is a limit, dictated by the ability of the metal to withstand a person's weight during maintenance.
Recommended distances for different brands of corrugated sheets
Each brand of metal profile has its own unique characteristics. Support profiles (indicated by the letter H) have a wave height of 44 mm and higher, which allows for sparse sheathing. Wall profiles (letter C) with a low wave require frequent support. Universal brands (NS) occupy an intermediate position.
Below is a table showing the dependence of the sheathing pitch on the grade of material and the angle of inclination. These data are averaged and are valid for standard snow loads.
| Brand of corrugated sheet | Angle up to 15° | Angle 15-30° | Angle more than 30° |
|---|---|---|---|
| S8, S10, S20 | Solid | 300-400 mm | 500-600 mm |
| NS35, C44 | 300-400 mm | 600-800 mm | 1000 mm |
| H57, H60 | 600 mm | 1000 mm | 1500 mm |
| H75, H114 | 1000 mm | 1500 mm | 2000 mm |
It is important to understand that metal thickness also makes its own adjustments. If you use a thin profiled sheet (0.4 mm), the pitch should be reduced by 15-20% relative to the table values to compensate for the low rigidity.
Materials and cross-section of bars for the frame
To create a high-quality base for a profiled sheet, an edged board or timber is most often used. Board 32x100 mm or 50x100 mm in size is the standard for most private construction projects. It is readily available, easy to install and provides sufficient strength.
If you plan to install heavy grades of corrugated sheets or the sheathing pitch is large, it is better to use timber with a section of 50x50 mm or 60x60 mm. The timber is less susceptible to twisting when drying, which is critical for maintaining the geometry of the roof. All wooden elements must be treated with antiseptics and fire retardants before installation.
A metal profile can be used as an alternative to wood, especially if the rafter system is also metal. In this case, fastening is done with metal screws. However, wood remains the more popular choice due to its low cost and ease of processing. hand tools.
Can I use unedged boards?
The use of unedged boards is highly discouraged. Bark and bast debris provide an ideal breeding ground for wood-boring beetles and mold. In addition, uneven edges make it difficult to accurately install and fasten the corrugated sheet, which can lead to deformation of the roof.
Do-it-yourself lathing installation technology
Installation begins with installation cornice boards, which is always attached first and has a larger cross-section, since it bears the main wind load and the weight of the drain. Then, using a template or tape measure, the installation locations for subsequent elements are marked.
Fastening the boards to the rafters is done with nails or self-tapping screws. The length of the fastener should be equal to twice the thickness of the board to ensure reliable fixation. When using nails It is important not to split the wood, so for hard wood, holes are pre-drilled.
During work, it is necessary to constantly monitor the plane of the slope. Sagging is unacceptable, since the profiled sheet will repeat this relief, and waves will be visible on the roof. For pitched roofs, evenness is especially important, since water flows in one direction and any holes will become a place for moisture accumulation.
☑️ Checklist before installing corrugated sheets
⚠️ Attention: When installing the sheathing, leave ventilation gaps. Lack of ventilation under the corrugated sheet will lead to the formation of condensation and rotting of wooden structures.
Common mistakes and how to avoid them
One of the most common mistakes is saving on fasteners. The use of rusty, too short or thin nails/screws reduces the reliability of the entire structure. Fasteners must be zinc coated and suitable for the loads.
Another mistake is ignoring gain in places where chimneys, ventilation pipes or roof windows pass. Around these elements, the sheathing must be reinforced with additional jumpers, since here the integrity of the roofing pie is compromised.
Some builders forget about waterproofing. Even if the profiled sheet is laid perfectly, condensation from its inside will drip onto the insulation and rafters. The presence of a waterproofing membrane between the sheathing and the insulation is mandatory for year-round buildings.
Use a stretched cord (fishing line) along the slope when installing the sheathing. This will help to visually control the evenness of the laying of the boards and avoid the “wave” effect on the finished roof.
Frequently asked questions (FAQ)
Is it possible to install corrugated sheets on the sheathing in 1 meter increments?
Yes, this is possible, but only when using load-bearing grades of corrugated sheeting (H60, H75 and higher) with a metal thickness of at least 0.7 mm and with a roof inclination angle of more than 15 degrees. For conventional brands, such a step will lead to sagging.
What is the minimum angle of inclination permissible for a profiled sheet?
The minimum angle is considered to be 8-12 degrees, provided that continuous sheathing is used and the joints are properly sealed. For angles less than 8 degrees, corrugated sheets are not recommended due to the high risk of leaks.
Is it necessary to treat the sheathing with fire protection?
Yes, processing is required. Wooden structures under metal roofing are susceptible to condensation, which creates ideal conditions for fungus. Fire protection will extend the life of the roof for decades.
Which is better: nails or screws for sheathing?
Self-tapping screws provide a more reliable connection and are less loose over time, especially under wind loads. Nails are acceptable, but require strict adherence to driving technology and wood quality.
A correctly calculated sheathing pitch is a balance between saving materials and guaranteed roof strength. Do not skimp on the frequency of boards if you are not sure of the accuracy of the snow load calculations.