The Rot Doctor


Subject: Joist Dry Rot
Date: Sat, 27 Nov 1999

In the crawl space under my house we have had some moisture problems. All of the moisture problems have been fixed and I have had 4 different inspections since then. I was told in all of those inspections that there is some very minor dry rot damage on the joists but that it is not bad enough to replace or repair. I was also told that the industry standard on this is that if at least 75% of the joist is good that I am okay. I am trying to sell my house and the last inspection I had the guy told me I had to replace most of the joists. He said he found 1/8 to 1/4 inch of damage on the joists. My joists are 8 inches. So in the worst case they have 95% good wood on all of them. My first question is do you now of the industry standard of 75% good wood? If so is that in writing anywhere? At what point would you recommend fixing the joists and how would you fix them?
Thanks for your help.

Well, there are no "official" standards that I know of. They vary from state to state and place to place. The 75% rule, however, is generally accepted and certainly within the standards of home construction. You are just facing a particularly cautious, or demanding inspector/buyer.

The underlying issue may be that they are concerned that the presence of existing rot, no matter how slight, indicates the presence of rot fungi or their reproductive spores in the wood, which it does. But it's also true that rot fungi are present in/on/around almost all wood. If the proper temperature/moisture conditions should recur then the rot in your joists would begin again.

I would suggest that your simplest and least expensive way of treating the problem would be to apply CPES (Clear Penetrating Epoxy Sealer) to the joists, particularly the areas where the wood is deteriorated. This will harden the bad wood and greatly reduce the chances that rot will recur in the joists no matter what the temperature/moisture conditions are in and around the wood. Inspectors will also like the hard wood. You should probably go one step further. After the CPES-treated wood has hardened, go back and spray the joists with disodium octaborate tetrahydrate (sold as Tim-Bor or Penetreat). This is a borate product that is generally known to reduce the chances of rot infestation, although of itself it will not harden wood and it will leach out under high moisture conditions. It's really a redundant treatment on top of CPES, but still one that inspectors should know about and a treatment that should make them happy.

We sell the CPES directly and ship daily via UPS GroundTrac. The Tim-Bor or Penetreat is sold by specialized lumber and log home outlets. You should be aware that the epoxy in CPES is carried into the wood by a powerful solvent mix and care must be taken not to breathe the concentrated fumes for any length of time. We use a mask with filters capable of filtering organic solvents (about $25.00) when working in enclosed spaces.

Hope this is helpful. Come back if we can answer further questions.


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