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Building Homes or Extensions/Patio Cover

Expert: Dave Johnson - 2/18/2009

Question

Thanks for taking the time to look at my question. Ok so here’s the scenario…I extended my current concrete pad to be about 20’W x 18’D. I want to build a fairly large patio cover covering this pad. My homes roof slopes down along the length of where the patio cover is to be. I attached a make shift diagram to better illustrate what I am trying to explain. Anyway I was planning on having a total of 5 posts around the perimeter and one a couple feet away from the house in the center, out from the house as far as the fireplace, to help bear the large span. (figures I could frame it that small area in as storage). I plan on using pine for all posts, beams and rafters. I want them all to be seen from underneath. On top of the rafters I was thinking of using 1”x whatever to cover the top. Shingles are what i currently have on my roof so want to continue that on to the patio cover. So my first question is on size of timbers. Here’s what I was thinking:

Posts: (6) 8” x”8” x whatever height they need to be.

Perimeter beams: (4) 8”x 10” x 9’ and (2) 8” x 10” x 10’

Rafters 4” x 8” x however long they need to be.

Center beam: (1) ?????? was told around 8” x 12” x 24’ or 10” x 12” x 24’ What do you think?

So I need to know if these sizes are adequate given my design? Is it overkill or do I need even larger? Remember I was going to use pine (for cost reasons) but is Douglus fur a better choice? Maybe just for the large center beam?

Thanks for any help you can give thanks.

Answer
Hi Eric,
The rafter sizes depend on the spacing. If they are 24" o.c., they would be fine at 2"x8". The wider the spacing, the heavier the rafter.

The posts and beams are a little over, and I'd rather see the side-wall beams be continuous. I also think you will be happier with some joists (like ceiling joists) to keep the rafters from spreading the sidewalls outward. The center beam carries little weight, and in conventional framing a 2"x10" would be fine, its just to keep the rafters in line and help from twisting.

Douglas fir is better, but if you frame the way you're talking about, pine will be fine.

By the way, your drawing is way mnore than I usually get, and it goes a long way in making things clear!!

please mail me again if this isn't clear..........
Dave