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Jabberwocky
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# Posted: 19 Jul 2016 11:03am - Edited by: Jabberwocky
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The long story short on this question is this: Does a composite 2x4 (nominal) board have more compressive strength than a wooden 2x4? I would think so, but because composite boards seem to only be sold as decking material, I can't find any information pertaining to other uses.
The reason I ask is because someone is advertising composite boards to be used as footer boards around the perimeters of sheds and small cabins. Seems like a great idea since this would elevate the bottom log/whatever 1.5" and keep it out of moisture. But it isn't a great idea if your cabin or shed crushes the composite board, leans over, falls into the swamp..... you get the idea. 
*Oh, and I should specify, I think the idea is that these would be laid flat on a slab foundation simply to lift the outer perimeter wood out of puddle zones/moisture wicking; they wouldn't be used to support walls over any open spans.
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sparky30_06
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# Posted: 19 Jul 2016 03:13pm
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I don't think composite has a structural rating like traditional lumber has.
Why not just raise your slab foundation before you pour it or build it out of the puddle zones??
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Jabberwocky
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# Posted: 19 Jul 2016 05:49pm
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sparky30_06
Why not indeed? Yes, I'm pretty sure you're right after digging up some technical specs on composites. They are more akin to particle board than solid wood. It baffled me that this was being recommended as a potential solution, but nonetheless IF it indeed worked in theory I could see the benefits, hence the questions I posed here.
After spending part of my weekend replacing rotten footer boards in my old barn, I was just trying to come up with more durable ways of doing things for my next project... Alas, I think you're right, the better solution would be to make the foundation higher and use pressure treated real wood.
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FishHog
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# Posted: 19 Jul 2016 06:13pm
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I think it would work fine. They are solid used that way. You won't crush it. It wont transmit moisture. I'd do it
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moneypitfeeder
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# Posted: 19 Jul 2016 06:56pm
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I'm not sure about the strength of the composite boards, but my better half did point out that in our cabin environment (upstate NY) there are plenty of critters that love to eat anything plastic or vinyl. Something with the salts used to make them or something. They have chewed all the new windows that we have installed! We have a lot of boards we need to replace too, and this caught my eye, but I think we'll have to stick with PT.
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sparky30_06
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# Posted: 20 Jul 2016 06:31am
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If your replacing rotten footer boards you need to ask yourself why are the rotting?? is it cause the foundation is to low and water is sitting against then and not draining properly?? is it cause there are no gutters or large enough overhang to keep the rain splash off the wood?? Was the wood not continuously sealed or painted to keep water from absorbing into it?
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Jabberwocky
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# Posted: 20 Jul 2016 09:38am
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sparky30_06
Yes, the barn is at the bottom of a slope and water ran right into part of it until I trenched around the perimeter. There are no gutters, no overhang. It was originally built by an old farmer in the 1980s with whatever scraps he had lying around. While it's miles more fundamentally sound than "The Shed of Doom," it's still pretty, shall we say, 'weathered.' Don't even get me started on the electrical[!]. 
It's still useful for storage and a workspace, so I've been patching up the most serious of problems, but I brought this subject up more out of curiosity than anything else. Again, just thinking of ways to make any future project more durable.
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sparky30_06
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# Posted: 20 Jul 2016 09:45am
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I grew up dairy farming so I know how things get built by an old farmer. And farm electric we won't even talk about that. I was an electrician for almost 20 years and rewires ALOT of farms, was amazing they worked and never burnt down. Some folks just don't think about water run off and a lot of other things. Sounds like your trench will help divert the water, replace them with pressure treated and you should be good for several years, I would coat them every year with an oil based stain. Now the old farmer I grew up working for would save his old motor oil and we would use that to water proof the bottom board around some of the sheds. That might be frowned upon by some folks these days.
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Jabberwocky
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# Posted: 20 Jul 2016 06:02pm - Edited by: Jabberwocky
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Ah yes, the ole motor oil trick. Well it probably isn't any more harmful than wherever else it ends up, other than that place is somewhere else.
I replaced the footers with new pressure treated lumber. What once was the worst room is looking pretty good now- I insulated the walls and roof underside so my wife has a nice workspace for her business. Next is getting some plywood up to protect the insulation and keep mice out.
An electrician friend of mine is gonna come help me sort out the wiring a bit for the cost of a couple beers lol.
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bldginsp
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# Posted: 20 Jul 2016 08:19pm
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I wonder how composite sills would do in terms of holding nails. The exterior plywood has to be nailed to the sill to be connected to the foundation. If the nails easily extract from the plastic, they won't help much when the hurricane or earthquake hits.
Can you divert the water away from the barn on the uphill side?
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KinAlberta
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# Posted: 20 Jul 2016 08:41pm
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I've long thought that if I were to build a shed or garage on a concrete slab, I'd lay down a composite deck board to gain an inch of lift up over any water seepage. I think I'd use the mostly plastic boards or one that impervious to water since that's the whole point of the exercise.
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sparky30_06
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# Posted: 21 Jul 2016 06:34am
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bldginsp
I would think instead of nailing the exterior plywood on you could screw the bottom down into the plastic board and that would give you the sheer incase of mother nature blowing and shacking.
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Jabberwocky
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# Posted: 21 Jul 2016 04:41pm
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Yeah, I could see nails being a problem, but I would think screws would do the trick. I use screws 90% of the time anyway 'cause I'm too lazy to hammer and I like my thumbs the way they are lol.
Again, I'm not going this route and already have everything sorted out drainage-wise. Over time the grass/dirt level had risen above the sill of the slab, but I dug a trench and channeled it around the edge of the building so it's all good now.
This topic was just a result of my brain going "Hey, what if....? Why not...? Lemme see what others think...!"
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sparky30_06
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# Posted: 22 Jul 2016 06:35am
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Some of the best ideas come from sitting around drinking a beer after building something and saying "what if we would have"
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