# Pergola construction - beam span without sagging



## Ron6519 (Mar 28, 2007)

The 2x6's are under sized for the span. Minimum 2x8's, but I would do 2x10's for the over built catagory.
Ron


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## fahartle (Jul 23, 2010)

Thanks Ron. 2x10s all around sound pretty doable. My better half wants to space the top boards further apart so there'll be fewer up there (so probably no increase in cost to use 2x10s).

What type of wood would you use for the pergola? I'm bad at regular maintenance, so I'm hesitant to use standard fir if I'd have to seal it every couple years. But I also hear PT boards can get twisty as they dry. We're in a very dry area, but there'll be snow sitting on the boards for a couple months in winter. Thanks,
Brandon


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## Daniel Holzman (Mar 10, 2009)

In dry climates you can use untreated fir for the framing, assuming there is a roof to keep rainwater off the framing. If there is no roof, you can paint the wood. I would stay away from PT for anything but the posts, not necessary if moisture precautions are used, plus PT is toxic and expensive.

I have a shed for my lumber, probably similar to the type of structure you are planning to build, I did not use any PT lumber at all, should last 50 years since the framing stays dry.


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## forresth (Feb 19, 2010)

PT warps when it dries unevenly, as would any wood. its just that PT is usually wet when you buy it.


I wouldn't sugest using any wood other than rot resistant woods like cedar or PT for an outdoor structure like this. you cant seal it anymore once the vines are up. better make it maintenance free.

one nice thing about the larger lumber is it usually tends to be of a higher grade than the smaller stuff.

for added supoirt if needed, run diagonal braces from the posts. it'll be much stronger and look pretty good too IMO.


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## Ron6519 (Mar 28, 2007)

I don't know of too many woods, set outside, that are maintenance free.
Ron


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## forresth (Feb 19, 2010)

Ron6519 said:


> I don't know of too many woods, set outside, that are maintenance free.
> Ron


Cedar, Redwood and Tamarack come to mind. I'm sure there are others. Ipe and Mahogany maybe


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## Ron6519 (Mar 28, 2007)

forresth said:


> Cedar, Redwood and Tamarack come to mind. I'm sure there are others. Ipe and Mahogany maybe


So you're saying these woods will last as long untreated(stained painted, etc..) as treated? 
Ron


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## forresth (Feb 19, 2010)

A raw cedar shake or shingle roof will outlast an asphalt shingle roof. a cedar post will last 20 - 30 years or more half burried. and that is the absolute worst case scenario for rotting wood. I've heard Tamarrack is better. I'm not sure how redwood lasts in the ground, but it does exposed quite well. The redwood porch on this house seams to be lasting comperably to the pressure treated decks. Hard to find redwood any more. I've heard it all gets shipped to Japan these days.
one thing about PT is every so often you get a board that hasn't been permiated all the way (most often 4x4s) and they rot out from the inside.


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## fahartle (Jul 23, 2010)

Thanks again for all the help guys! My job got a tad easier because we found we couldn't really afford the 12x24' deck. So we're going to downsize a bit to a 10x20' which I'm guessing will help out the spanning issue. After the advice I think I'll go with PT wood all around. Maybe next summer I can put on a good sealant as that summer project. Thanks!


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