What is the correct distance to fix the rafters?
Construction is not easy. It is necessary to take into account many important things and small details, on which the reliability of the building will depend. An important building element is the roof. In order for the roof structure to be strong, you need to correctly install the rafters, securing them at a certain distance. On which one - read below.
The distance at which the rafter legs are fixed is called a step in construction. On average, it varies from 60 cm to 1 m. But it can reach 2 meters. The following characteristics affect the size of the rafter step:
- Pitched roof type (single, double, or multi-slope)
- Tilt angle of the structure
- The thickness and width of the rafters
- Structural loads (snow, wind. You can see them in the maps of SP 20.13330.2011 “Loads and Impacts”.)
- Roof type and sheathing sizes
Distance between rafters based on roofing material
Roofing materials have different weights and types of installation, therefore they have different loads on the roof. The builders have developed recommendations for the selection of the distance between the rafters for each type of roofing materials. Recommendations are relative. They do not take into account many indicators of the roof structure, load volume, climatic features of the region.
Decking. Due to the low weight, a step of 0.6-1.2m is acceptable. When using a rare step of more than 80 cm, it is worth increasing the cross-sectional area of the rafters.
Ceramic tile. It is about 5 times heavier. Therefore, a frequent step of 60-80 cm is used.
Metal tiles. For this type of roof, a step of 60-100 cm is enough. due to the reduced pitch of the lathing (about 30 cm.)
Ondulin. Apply a step of 0.6 m. When the roof is tilted up to 15 °, 0.9 m. - when tilted from 15 °
Slate. The rafter distance can vary from 60 to 150 cm. Most often they take a step of 120 cm. The dimensions of the timber should be used larger than those of other types of roofing materials.
Calculation of the distance between the rafters
There is a simplified calculation option. It is presented below. But here only the dimensions of the rafter bar are taken into account - its length, width and thickness.
To determine the distance at which the rafters will be attached, you can use fairly simple calculations.
· Find the approximate rafter pitch for the roof type recommended in your area. You can find wind and snow loads of the region in the maps of SP 20.13330.2011 “Loads and Impacts”.
· Determine the size of the roof - its length. This dimension must be divided by the recommended rafter pitch. Add 1 to the resulting coefficient. You will get the number of rafter legs that are required for one pitched side.
· The length of the roof must be divided by the number of legs obtained. This number will be the final rafter distance.