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Home >> Articles >> Water - good for us, not our homes, Part 3 - Wood Rot
 From The Best Times - September 2003By Don Carter, Structural Engineer Perhaps you have noticed the high number of window replacements working throughout Johnson County. It seems that I see a window crew at least once a month on my south side walking route. Yet, in the ‘60s era neighborhood from which I moved after nearly 40 years, I don’t recall a single neighbor having to replace windows. Puzzled by this I asked a window contractor why things are so different now, and here is his explanation: • Wood windows produced in the last couple of decades are made from second-or even third-growth timber. This means their lumber came from trees of approximately 25 years age that were planted to replace first-growth trees that had stood for hundreds of years. Older windows were made from the older trees, which typically meant denser wood with greater decay resistance. • Lead-based paint was a standard exterior primer up to 1978 and, notwithstanding the downside, it did a powerful job of protecting wood against moisture. More so than today’s replacement paints. • Lawn irrigation systems are more common now and often they are incorrectly set to sprinkle windows several times a week, all summer long. Thus the wet-dry cycles experienced in just one summer may equal that of several years in my old, un-irrigated neighborhood. All of this made sense to me and I began to notice other house locations where wood does not seem to hold up as long - such places as exterior trim, siding bats and facia boards. Since there is nothing we can do about second-growth lumber or lead-based paint, it seems our only recourse is to preserve lumber by controlling the water. Once again WATER is our issue with Part III focusing on wood rot and its prevention. We should start with proper nomenclature. Some people use the term “dry rot” when describing damaged wood. Dry rot is a potato problem. All wood rot is caused by decay fungi, which grow on wood with a high moisture content. Decay fungi are living organisms that send minute threads called “hyphae” through damp wood, taking their food from the wood as they grow.1 Gradually, the wood is decomposed and its strength lost. Such damage is often inconspicuous until the final stages when there may be a sudden failure. We use an ice pick to probe suspect areas, and you can do the same at your house. Catch the problem early, and restoration is less costly. The key to preventing rot is to control the wood’s exposure to moisture. When dry wood comes in contact with moist soil or recurring water exposure, it is likely that wood decay will occur. Rain leaks, faulty plumbing and leaky downspouts are common sources of the moisture that causes rot. Most wood-rotting fungi rely on a direct supply of water right at the site of decay. When all exposures to moisture are eliminated, decayed wood will dry out and further decay will be stopped. When replacing a segment of wood that has rotted, do it with treated wood cut to fill at least one foot beyond the rotten area and avoid placing new lumber in a position where it makes any contact with old, decayed wood. Part 1: water control • Part 2: mold control 1 Some science-related data for this report was obtained from Ohio State University Extension Don Carter is a licensed structural engineer and managing general partner of Foundation Engineering Specialists LLC, a company specializing in residential design and assessments.  |
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