A.Bill Rose, architect and building researcher at the University of Illinois Urbana-Champaign, responds: You want the crawlspace to be clean and dry when you’re finished. First, do whatever is necessary to make sure that rainwater cannot enter the crawlspace. Install gutters at the roof eaves, if necessary. Be sure that the discharge ends of any downspouts are as far as possible from the foundation. Keep the exterior grade at a minimum 5% slope away from the foundation, for a good 10 feet. If there is a persistent wet spot in the crawlspace, install a sump pump there. The existing concrete slab will be enough to keep evaporation from the surface down to a manageable level.

Any work in a smelly crawlspace should be approached as a mold remediation project. For any overhead work, goggles are a must. If the expected amount of visible mold colonization is minimal, then N-95 respirators and gloves should offer good protection. If the anticipated black area is large (more than 2 square feet), then P-100 respirators and...

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