Expert: Dave Johnson - 5/31/2007

Question
Hi.. I'm planning on building a pergola.  If the beam span is 18' and the rafter span is 18', what size should the rafters be?

Answer
Hi Rich,
First, the beam. If you are going to have multiple posts or columns, the beam size can be reduced. (most old pergolas have several columns)
As far as the rafters go, 2" x 12" is ok for this span, however if you go to a 3" x 10" there will be less warping and it will look better as well.
The ledger should be 12" and lagged to your house studs.
Good luck, and if I can be of more help, mail me...
Dave