Case Studies

Crawl Space Insulation Case Studies: Crawl Space Repair in Williamsburg, VA

Tuesday, July 9th, 2019 by Erin Dougherty


A homeowner contacted us about his home in Williamsburg, VA. He had concerns about falling insulation and mold in his crawl space.

Jamie did a thorough inspection of the homeowner’s home and identified some key issues. The current 6 mil vapor barrier in the crawl space needed to be replaced – it was unsealed, the seams were not taped, and it was letting in moisture. The existing fiberglass insulation was falling from between the joists, which meant it wasn’t providing any insulation in those areas. Finally, mold was growing on the joists which indicated a high relative humidity and the presence of moisture.

Mold in the crawl space is often a result of a build-up of moisture. Mold needs three things to grow; a relative humidity of more than 60%; warm temperatures, usually above 70 degrees; and organic material, in this case, the wood floor joists. Crawl spaces often offer these conditions and are therefore an ideal environment for mold growth. This mold growth can present a few problems, it can compromise the air quality of your home (50% of the air you breathe in your home comes from the crawl space) and over time, the mold can damage wood joists and causing wood rot and compromising the integrity of your home. 

Insulation in the floor joists can cause several problems. First, gravity eventually has an effect and the insulation begins to sag and fall over time. In addition, most fiberglass has a paper backing, this is an organic material and allows mold to grow on it. Fiberglass insulation in between the joists holds moisture and can saturate the joists promoting mold growth. Finally, fiberglass allows a lot of air to pass through it and does not provide a high enough R-value to keep your floors warm in the winter. 


To address the homeowner’s concerns, we first needed to clean out the crawl space and remove any debris, and all of the old insulation and vapor barrier. Then, we applied an antimicrobial to the joists. In this instance, we used a product called Mold-X2. Mold-X2 is a two-part application utilizing a stain remover and a botanical. The stain remover is applied first and acts as an antimicrobial, fungicide, and disinfectant. The stain remover removes stains in 20 seconds and is followed by the botanical which is a cleaner and deodorizer. 

We proposed a 20 mil CleanSpace vapor barrier. This product is a 7ply, reinforced polyethylene liner with an antimicrobial built in. When installed, the seams are overlapped and taped with a special 4-inch-wide tape that is extremely durable and does not allow the liner to separate. The liner is also attached to the crawl space walls 6 inches above the outside grade. The purpose of this is to seal the crawl space off from the earth and prevent moisture from entering the space.

We offer customers several options to insulate their crawl space walls. The homeowner opted to use our 1.55-inch Foamax Foam Board Insulation on his crawl space walls. This insulation provides an R-10 (resistance to heat value) and offers air sealing when the seams between the foam panels are sealed. These foam insulation panels are installed over the vapor barrier on the crawl space walls. This extends the thermal barrier of the house from the ceiling of the crawl space, to the floor of the crawl space. This insulation is also made of inorganic materials which means it will not support mold growth.

We also sealed the sill plate and installed an interior friction fit door behind the exterior crawl space door. Together these solutions will help keep the homeowner’s crawl space dry. However, since he did not opt to install a dehumidifier in his crawl space, The homeowner will need to monitor the relative humidity in his crawl space using a hygrometer. If the relative humidity remains over 60% for a prolonged period of time (approximately a week) we suggest installing a dehumidifier to help prevent mold from growing again. 

Project Summary

Foam Board Insulation: Foamax

Vapor Barrier: 20 mil CleanSpace

Mold Rememdiation: Mold-X2

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236 Industrial Blvd
Suite A
Toano, VA 23168

The Drying Co./ThermalTec
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Toano, VA 23168
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