Expert: Bruce E. Johnson - 4/27/2009

Question
Morning Bruce,
We are a very handy at DIY projects but need some assistance with the recommended dimensions of our materials. We are building a front deck at the entrance of our home with a pergola spanning the width of it. The pergola will be free standing and not attached to the house because of a bay window, we will be using Western Red Cedar for the pergola, the four corner posts will be incorporated into the construction of the deck, the remainder of which will be constructed of treated lumber covered by composite decking materials.
My question is with regard to the cedar materials for the pergola, the span of the beam width from post to post is 17 feet across the front, we cannot add a third post without blocking the front window or hampering the stairs. The span from front post to back post is 12 feet. We plan to notch the posts for the beam... what size do you recommend for the four posts and how large should the beams be? We live in Utah so there will be a snow load but the top of the pergola will be left open, we had planned on using 2 X 6 X 12's for the cross beams at 16" centers. The pergola will also be additionally strengthened with the construction of the handrail between the posts. We want a beefy look and solid construction, the discussion has been on 6 x 6 or 8 x 8 posts and 4 x 10 x 20 or 4 x 12 x 20 for the beams but of course cost is always a consideration.
Any help and suggestions you could give us would be greatly appreciated.
Thank you for your time,
Victoria

Answer
Hi Victoria, 6x6 posts are fine, 4x12 beam at least..but a 6x12 will work better with the 6" posts or you can sandwich a 2x12 on each side of the posts.  If you go with the latter you will need spacers in between to keep the beam uniform..the joist size is adequate if you put the crown up (the hump of the wood always goes up to counteract the force of gravity). I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com