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Old 05-20-2011, 05:10 PM   #1
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span and lumber size requirements

What determains the span spacing, and the size of lumber to be used. I will be building a 40' long by offsetting 14' and 12' back yard patio cover. Other than code requirements, is there a general rule out there on size of lumber, spacing of rafters, and size of decking. Here's an example of what I am looking for. If I use 2x6's on 16" centers, VS 2x8's on 22-24" centers I will save $50 for just the trusses (or runners) using the 2x8's. Could I possibly go with 2x6's on 24" centers if I were to increase my decking to either 5/8's or 3/4? I am looking for a general rule of thumb rule here on what tells me I can increase span, enlarge lumber and save $ doing so, but maintaining the stregnth and durability in our TEXAS wheather. BTW; I will be installing a metal (steel) lifetime roof on top. And Yes I want to walk on this overhang with out feelling that spongee week feeling.
Here's what I would like to do: 2x6's on 24" centers, with decking 5/8 to 3/4, paper then metal roofing.

One more question, I live in Dallas Tx. area. If I am going to enclose the lower surface area of this patio cover, (hide the rafters), does anyone out there think I still need to use PT wood rather than reg. #2? My general rule is if it's exposed go with PT, if its covered and protected from weather go with reg #2. Just wondering about the moister in the air absorbsion as far as long lasting... Any info will be greatly apprieciated...


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Old 05-20-2011, 05:15 PM   #2
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If it is going to be subjected to any weather, you need to use PT. The cost upgrade is minimal. As far as the lumber spacing, it will all be determined by the span between beams. For a floor, 24" on center is not considered optimum. The decking will give between the joists. 16" on center is what is generally accepted. Using a 2x10 on a 24" center vs a 2x8 on 16" centers will probably not save you any money anyway. You will need to check span charts to see how far you can safely span. But keep in mind, a maximum span will probably give you that bouncy feel that you don't want.


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Old 05-20-2011, 05:37 PM   #3
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You should imquire at your local building department before you go off half-cocked and poorly informed and have to take apart something you have built. That mistake will cost you a lot more overall. You'll need a permit anyway.

The Inspection Office can make recommendations and probably even furnish you with mini plans.
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