With rafters it runs in perpendicular from the walls to the ridge while with purlins it runs to the ridge in parallel.
How to support roof purlins.
Have them installed by following the edges or sides of your roof.
Using a combination of rafters and purlins is common.
Placing the roof along the perimeter of your roof is.
Snap a chalk line horizontally across the roof two feet down from the top.
Once your purlins have been fitted and a supporting framework has been created you should look to carry out an inspection before you continue work.
The use of purlins as opposed to closely spaced rafters is common in pre engineered metal building systems and both the ancient post and beam and newer pole building timber frame construction methodologies.
Lay the first purlin at the ridge.
The support system for the roof is comprised of ridgepole and rafters or purlins.
How to install metal roof purlins.
Due to the angle that created in the valley it is necessary to double the purlins.
Double them up in valleys.
How to support roof purlins.
Purlins can be fixed to rafters and all joins and laps should be supported by a rafter.
Here are several useful tips for purlin installations.