Just bought a 25 year old home that has improperly installed insulation in the crawlspace. The insulation is fiberglass rolls with a paper backing, and is installed with the paper facing down, toward the ground. When the home inspector and I explored the crawlspace, we could see green mold growing on the joists where we pulled the vapor barrier aside to peek up into the cavity.

The source of moisture seems to be a concrete pad that butts against the foundation and collects water from the shed that sits atop it. I plan to remove that shed and the concrete pad before doing work with the insulation.

I intend to replace the insulation with either the same type or a plastic vapor barrier cut to fit between the joists and un-faced insulation instead. The new insulation will be installed with the vapor barrier facing the living space.

My question is about the mold: once the old insulation is pulled out of the crawlspace, how should the joists and flooring be cleaned to inhibit further mold development? Is there a recommended time period to leave the joists exposed to dry? I will be doing this in the Fall when we are likely to have dry weather, and outside temps will be closer to inside.

  • one recommendation, after removing all the old insulation, hire yourself an "industrial" dehumidify & run it for a week in your crawlspace.
    – Mike Perry
    Jul 24, 2011 at 23:38
  • Good idea. I suppose one should avoid spreading spores to other areas of the building, or in my case, into neighboring houses - most large dehumidifiers I've seen move a lot of air. The EPA guide linked in my answer has info on containment.
    – Eli Heady
    Jul 26, 2011 at 1:03
  • all I know is, my wife works in the engineering department of a (large) hospital, and when some of the older buildings flood, the maintenance crews go in remove all water damaged materials, then set up huge "industrial" dehumidifies & let them run for a week before going back in & repairing the damage...
    – Mike Perry
    Jul 26, 2011 at 1:18
  • If you remove the all sources of moisture that the mold needs to grow you will not get any further mold development.
    – Walker
    Jul 26, 2011 at 11:13
  • I wouldn't put fiberglass insulation back in. Look into the alternatives (i.e. reflective foil wrap or board insulation). The fiberglass fiber insulation will hold moisture and as you know, isn't exactly fun to work with either. Also, put a good vapor barrier on the ground, not up against the joist. In any case, of course, get rid of your moisture problem first :).
    – Justin
    Feb 19, 2015 at 14:14

2 Answers 2


Assess the damage:if moderate, try removing the mold yourself. Use fans to move the air and flood lights to see and plastic covers to collect the mold when scrapped clean. Use liquid spray that you can buy at the hardware store.Some suggest surface blasters. After the mold area is clean and dry put in a dehumidifier and check for ventilation as preventative measures.


I've found some good guides about this, so I'll share them here. I won't be accepting this answer, so if anyone else has something to add, please do.

The US EPA publishes a guide on mold remediation in commercial buildings, much of which seems applicable to residential buildings also. The guide recommends three methods to clean wood surfaces smaller than 100 square feet: wet vacuum if the area is still wet, damp wipe with detergent, and HEPA vacuum when dry.

The guide also provides advice on what protective equipment is required for cleanups of varying sizes.

The Washington State Department of Health publishes a guide that provides much of the same information as the EPA guide, but has an additional recommendation about treating surfaces with a cleaner containing borate to inhibit future mold growth.

Any remediation activities should be performed after the source of moisture is identified and removed.

I suppose the best advice is probably to consult a reputable remediation professional, as molds are allergenic and some are toxic, even after they are dead. The resources I've found suggest hiring a pro for cleanups of any area larger than 10 square feet. If performing the remediation yourself, take all necessary precautions to protect your health and to limit exposure to building occupants, and of course don't rely solely on this answer for advice.


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