Criterium Engineers: DRY ROT -- Slow and Persistent

DRY ROT -- Slow and Persistent


	Dry rot is actually a bacterial action supported by the simultaneous presence of warmth, darkness and moisture.

If you expose a piece of wood to water it will rot.

That is commonly known. In the extreme, unusable "mush" remains. The wood fiber essentially dissolves. While this is commonly referred to as rot, it is more accurately called WET rot. A more insidious rot is DRY ROT. While moisture is important to dry rot, only minimal amounts are needed. Often, in fact, high humidity is enough.

Dry rot is actually a bacterial action supported by the simultaneous presence of warmth, darkness and moisture.

Thus, removing any one of these elements will usually slow or totally stop the progress of dry rot. Dry rot is quite common in many coastal parts of our country due to the relatively high humidity. Areas where wide temperature cycles produce condensation are also vulnerable.

Of particular concern are homes with inaccessible and poorly ventilated crawl spaces and attics. Here the needed combination of warmth, darkness and moisture is common. Often, the results may go unnoticed until a serious structural problem develops.

Older homes which have recently added insulation to help minimize energy costs are especially vulnerable.

Dry rot didn't develop before because the natural "breathing" of the home prevented the simultaneous presence of warmth, darkness and moisture. In the winter, condensation occurred, but the temperature was cold. In the summer, warmth was present, but the walls dried out as the house "breathed." When insulation is introduced, the walls can no longer breathe, the condensation doesn't dry out and dry rot develops.

Once established, dry rot is difficult to stop fully.

While it is a slow process, often requiring decades to develop into a serious structural problem, it is persistent. Unless steps are taken to control dry rot, it will become a serious problem.

Here are some suggestions to minimize the risk of dry rot in your home or building.

Make sure you have access to all crawl spaces and attics.

Make sure that all crawl spaces and attics are well ventilated. A good rule of thumb is to provide at least one square foot of ventilation area for each 150 square feet of attic floor area and each 150 square feet of crawl space area.

Make sure that crawl spaces are well drained. Water should not be allowed to stand in these places.

In crawl spaces, apply heavy polyethylene (plastic) over exposed dirt floors to control moisture.

Make sure that moisture barriers on insulation are on the heated side only. In the basement, that means no moisture barrier should be on the underside of the insulation.

Cathedral ceilings with insulation sandwiched between the ceiling and thee roof should be vented at the eave line and at the ridge.

In attics, insulation should be along the floor, not along the roof.

Always be alert to paint peeling from the outside walls of your house. If a pattern is apparent (the peeling is worst along the bottom), the walls should be investigated for possible moisture accumulation. While peeling paint may be the obvious problem, dry rot in the walls may be far more serious.

Finally, no wood siding should be in contact with the ground. Normally, at least a six inch separation is recommended.

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