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| Posted By |  Subject :Treated wood question |
Last summer I had a buddy with a cat prepare a site for my pole shed/shop. He pushed all the topsoil into a pile and leveled the site with clean sand and then added about 4 inches of good gravel on top. So I'm sitting with an 80'x 60' parking lot. I would like to start the actual construction this year and my questions are:
What's the consensus on the newer non-arsenic treated timbers underground? Will they last more than 20 years? If there is a problem would some sort of water repellent be a good idea for under the ground line?
I hope to live more than 20 years :) and if the timber life is going to be limited I would most likely put up a stick built building with foundation or floating slab.
Thanks in advance,
Dave
| Have you considered using concrete pyramid type piers to rest the support poles on or if you want the pole in the ground; you could encase the wood in cement. Either way keeps the wood out direct contact with the soil and a tempting meal for termites.
Around my area, even the best pressure treated wood will not last as long as 20 years without pesticides. I just recently had to pull up and remove some pressure treated landscaping timbers that fire ants had infested. These timbers were still green from the treatment and not very old. I would estimate they had been there for maybe a 2 years.
Something else you can do and I realize that the environmental aspect of this will probably cause some desenting opinion is to treat the area ground around the timber with diesel fuel. Termites and bugs will not go near it. As long as you don't use an excessive amount, it should not cause any problems.
About the only pesticide that really worked for applications like this was Chlorodane, but the EPA banned it MANY years ago. Dursban did not work nearly as good and now it is being phased out. The newer pesticides are ineffective at best and a waste of money at worst.
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If the wood is installed right I don't see any real need for ANY protection by chemicals.
Our equipment shed at the farm was built many years before I was, and none of the posts are showing any deterioration at all. I think it was built around 1955 as I recall.
The posts stand in holes with a minimum of 6" of pea-stone (very fine gravel the size of peas) under and around them, this allows for good drainage.
Encasing any wood in concrete is just asking for trouble, it holds the moisture against the wood and promotes rot. If you look at the brackets hey sell for mounting posts on top of concrete peirs you will see that they are formed in such a way as to hold the post up of the concrete slightly, this is to keep them dry.
Best of luck.
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Randy, One of the good things (maybe the only one) about living up here where it gets to -40 degrees is a definite lack of termites. I don't think I've ever seen termite damage. We do have ants that can destroy wood but that's usually above ground level.
Placing the poles on concrete piers would work. Then I'd have to build a highly braced framework similar to a timber frame because the ground would no longer hold the upright poles rigid. I got my sawmill running last fall so all the non-treated inside framework could be just made from pine (free!!). I would still buy the trusses though. Only the wood that touches the concrete would have to be treated. This could be a good way for me to "practice" on a simplified timber frame because I plan on building a timber frame house on this property in a few years. I've built two houses before this but they are traditional stick built houses.
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Murf, are you saying that you would expect the newer treated wood to last as long? If so that would make things alot simpler and less expensive.
Dave
FYI: Even though the prepared area is much larger I only plan on a 30 x 60 building. I might add a lean-to in the future though.
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You could use metal trusses. Pour a concrete pier for each leg.
You could use metal posts. Something like old drill stem.
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No Dave, I think you misunderstood me.
My point was, there is no reason I can think of to use 'commercial' lumber, treated or not, to build your structure. Properly installed, plain wood will last every bit as long as anything else. To me PT lumber was just a reaction to poor construction methods that resulted in a lot of rotted wood.
We have built many buildings with wood cut from or own lands, they end up as good or better than those made from 'store bought' lumber.
If you're interested I could point you to people in your area who will either sell you enough rough cut lumber, or bring in a portable sawmill for you to have what you need cut from your own trees.
Best of luck.
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My climate (Alabama) is different from yours, but I have never had a rot problem with PT lumber in ground contact. The new formula is an unknown, but I think it will perform comparably. I have used it for a fence, and my biggest complaint is the corrosiveness -- you must use double galvanized or stainless fasteners. I don't have freeze-thaw worries, or frost heave, but I imagine you have less termite and other organic problems to deal with. The biggest threat to PT lumber in my experience is the effects of UV radiation from the sun, which won't be a factor in your application. I think if you dig your holes deeply enough to get below the frost line by eighteen to twenty-four inches, put a little gravel in the bottom, set the poles or posts, fill with concrete up to the frost line, then fill the rest of the hole with gravel, you will have a trouble free arrangement that will last indefinitely. You must have good compacted or undisturbed soil under the gravel under the post and good drainage away from the building perimeter. My guess (I'm no engineer) about the load is that it would be wise to have the holes, and thus the concrete around the posts, be two to three times the diameter of the posts. Also, I wouldn't rely much on the lateral force resistance of this arrangement unless you use either cross-diagonal bracing or sheathing to prevent racking. This may sound like a lot of work, but I think it is still less trouble than other options. I am assuming that you are not going with beams, floor joists and plywood subflooring. If you are, then I have a great design that uses no PT lumber. Let me know and I will share it.
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I did a little research on posts. Consensus: No body agrees. Barn builders say if the ground is well-drained then earth backfill is ok, seems logical (putting peagravel around the post, to my mind, would hold water and encourage rot--and over time, the air spaces between the peagravel would fill in anyway). Lumberyards say concrete around the posts encourages rot when the post shrinks the resulting gap fills up with water and cannot drain, and when it freezes will split the concrete. A company called FBi makes a square, hi-tensile, reinforced, corrosion-resisting concrete "pier" of sorts that sits below and above ground that you graft a wood post to with metal plates on either side. This seems like the way to go.
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I agree with the lumber yards. Forget the cement, I feel your asking for problems. Treated wood for the "under ground" would be my chioce of wood. I have a tree stand that was in the ground for more than 13 years now out in the woods, clay no drainage. Not a bit of shakyness in it yet. If you cut any ends though I would paint on a treating material to theat portion. I like the new woods and welcome it only thing I have my doubts about is if it will still have the wasp retarding properties that arsenic treated wood had.
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