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04-24-2007, 05:48 AM #1
Is dry rot progressive in absence of moisture?
Found a small area of dry rot at the end of a beam (actually 3 sistered 2x10's) where the beam is notched into the side of the foundation wall in a crawlspace. The dry rot appears localized to the last few inches of the beam next to the foundation wall, and does not appear to extend beyond the surface into the wood more than a 1/2-inch. No moisture present at time of inspection, and no obvious source of exterior water infiltration. There was no moisture barrier between wood beam and concrete, so I tend to assume the moisture was from condensation at the concrete contact point. Home is a 19 yr old log cabin. My question is this; is dry rot progressive, can the area of rot continue to expand in the absense of moisture?
04-24-2007, 06:39 AM #2
Re: Is dry rot progressive in absence of moisture?
Dry Rot is a fungus that eats the pulp of the wood. The name dry rot is a misnomer since all wood destroying fungi requires water for germination, growth and survival. It also needs a food source (the wood itself), a temperature range between about 40 and 90 degrees and oxygen. One might say that if you cut off the moisture source, you cure the problem. But can you be sure it will come back. Once established, the dry rot fungus can survive in wood as dry as 20%. That is why wood is kiln dried to 19%. In the absence of moisture it will hibernate. There is a correlation between the amount of moisture and rate of consumption/growth.
To answer your question unless this cabin is an area that typically has less than 20% humidity than the fungus will continue to grow but at a slower rate. I didn't see your location but suspect like many home there is a lot more than 20% humidity present. This is where a moisture meter is handy. Most sill plates I see have around 50% moisture which is rot out in older homes and pressure treated wood is used as a replacement. A couple strips of tar paper would have help in this cabin. Dry rot in this location will compromise the beams and if only one is bad at the moment the rot will in time take over the others as it grows.
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Last edited by Rick Bunzel; 04-24-2007 at 06:41 AM. Reason: correction