Quote:
Originally Posted by Snail
Another point about burying the timber inside the insulation is that it will dry out even further than kiln drying can achieve. This doesn't directly reduce strength but may cause cracking around the fasteners, which is worse if anything.
With design of timber structures, strength is not the only consideration. When the load is continuous, as it is here, long-term creep becomes the critical design factor. Unfortunately, the timber design code rules are mainly concerned to keep this creep to very low levels for aesthetic reasons in buildings. We can be a bit more relaxed for tanks, but I am not sure how much. Does anyone here have long-term experience?
Because timber inevitably moves a bit, the liner must be able to accommodate this movement. A few years ago I had a very bad experience with a paint-on coating on a timber deck. It was not extensible enough to take the movement and cracked after only a few years. Needless to say, I went back to the good old sheet Butynol after that. Possibly an outside environment, even in a mild climate is more severe than this one, but, on the principle of never buying version one of anything, I'd not be happy with any liner that wasn't backed up by a lot of years of successful experience.
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Hi,
The EPDM lined tanks of both lumber and metal go back to the 80's and have a good track record. They last longer than most commercial tanks, cost a small fraction of equivalent commercial tanks, and when the liner finally does go out, it can be replaced for a few bucks for another 20 years. They seem like a great all around value to me.
On the lumber at high temperatures, most solar heat storage tanks don't spend very much time above 150F, but I agree that it does add another good argument to insulating the inside of the tank.
I guess the one caution I'd offer is that its important to build a good structural design, and if you are not up on structural design and sizing techniques, its best to stick closely to one of the designs that have shown that they do work well.
Gary