Fight the Rot Within

By Andy Christie

Cottage crawl spaces are often attacked by rot, but it’s easy to fight – once you’ve found it. Spring is a great time for weekend warriors to do an annual inspection; all you need are knee pads and a dust mask (your armour), a knife (your weapon), and a light. 

First, examine surface-water control outside. When you walk around the cottage, are you ankle-deep in muck? A poorly maintained, or non-existent, eavestrough system lets rainwater pool near the cottage where it can infiltrate and damage the floor members. Check the lay of the land: If the ground slopes toward the building instead of away, spring runoff may be collecting under the cottage. Ground-level windows, vents, holes for pipes, and settlement cracks are also common, and easily fixed, entry points for surface water.

While moisture decay sometimes attacks the roof and walls, it is more common in the floor structure. So, head into the crawl space, but beware a few hazards of battle. Since wet ground plus live wires can kill, switch the power off. Move cautiously, watching for enemy nail points, broken glass, bees, wasps, cornered animals and, if you’re squeamish, spiders. Remember, it’s an adventure. Stab the sword, uh, knife, into joists, beams and sill plates – all of them, not just those near the entrance. A solid thunk sound is good, but if the knife penetrates more than three or four millimetres, the wood’s strength has beenaffected. It won’t take long to get a feel for wounded wood, but don’t trust appearances; wood can look quite sound, but have the texture, and strength, of sponge toffee when prodded. Conversely, some older woods might look dark and soft, but remain solid. 

Floor members rot when water leaks in or the humidity is too high. At the crawl space perimeter, expect the sill plates and the joist ends to be soft where water has infiltrated. In the middle, decay is usually caused by long-term high humidity, which can be reduced with cross-ventilation and a continuous vapour barrier on the ground. Once you’ve found rot, and addressed its cause, you may need to have the affected members replaced. And when you return from battle, don’t forget to turn the power back on.