With rafters it runs in perpendicular from the walls to the ridge while with purlins it runs to the ridge in parallel.
Rafter spacing for tile roof.
Rafter spacing rafters must be strong enough to hold the roof sheathing and the shingles.
To ensure this the battens should be at least 1 2m long.
Common spacing for trusses on this type of building is often between 2 and 4 feet but trusses built with advanced designs may allow spacing as great as 8 or 12 feet.
The support system for the roof is comprised of ridgepole and rafters or purlins.
Using a combination of rafters and purlins is common.
As a general rule roofs that have a high human occupancy rate should be framed with rafters every 16 structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes.
It is also important aesthetically so that the tiles on the finished roof are equally spaced.
Typical rafter spacing codes will specify a minimum spacing of 16 inches 19 2 inches or 24 inches.
The typical spacing standards for residential and commercial buildings are about 1 to 2 foot.
If your local building authority has a rafter spacing code you may not space rafters wider than required by code.
Use these two tables for roof rafters with a slope of 3 in 12 or less.
Battens should be fixed to rafters set at centres not more than 600 mm apart and should span at least 3 rafters.
The same concept holds true for roof trusses.