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Weisenberger 06-26-2018 10:14 AM

Deck roof
I was wondering if anyone can tell me what size of board I can span across my deck that is 18’ deep, I also would like to use 4x6 posts and also 4x6, for a header on the post’s. The roof will be 27’ wide by 18’ deep, any help will be great

carpdad 06-26-2018 10:30 AM

Re: Deck roof
6x6 for posts are better because you may want to notch them for header support, and less chance of twisting. Thinner always means more chance of twists and warps. Usual header is double 2x10 and all joints sitting on the posts. Posts for this kind of header are spaced every 8'. This is NJ and deck only without the roof. Floor joists also usually 2x10 (check the span chart and you want min 360 deflection) and spaced every 16" o.c.

Roof decks are usually made with 4x8' plywood, 1/2" ply/osb over rafters every 16". If you want a finished look deck, you want to install beadboard or t&g boards first, then another layer of 3/4" ply above it. This is for building up some thickness so that shortest roofing nails that are practical (1.25") can be used without going through all layers. If adding more materials, you have to account for that weight in your header/footing sizes. The posts must be braced in some way.

mark sr 06-26-2018 10:33 AM

Re: Deck roof
Are your footers sufficient to handle the extra weight of the roof?

Weisenberger 06-26-2018 01:03 PM

Yes it is supported good, the roof will tie into the side of my house and slope away from it, what I’m looking for is if I can use 2x8’s for roof joists or if I have to go bigger, the span from the house out to the end of my deck is 16’, I will be using metal for roofing material and I don’t believe there will be a lot of weight

carpdad 06-26-2018 03:13 PM

Re: Deck roof
I don't think 2x8x16'. Its own weight will bend it in the middle. Check the beam charts for double 2x8 or 2x10.
Also what kind of metal roof? Corrugated roof can be walked on if also supported between bays every 24 or 48" apart. If a flat metal roof, you have to lay down a deck first. That is more weight for 16' long rafters. Snow weights are also a factor.

Nealtw 06-26-2018 03:40 PM

Re: Deck roof
18 feet plus a slope= longer than 18 ft.
20' 2x10 will sag under their own weight.
I would use 2x12.

Weisenberger 06-26-2018 04:11 PM

Thanks for the great feedback everyone

Nealtw 06-26-2018 04:14 PM

Re: Deck roof

Originally Posted by Weisenberger (Post 5562129)
Thanks for the great feedback everyone

Perhaps trusses would be a better option.

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