Why Seal Your Crawlspace?
Reason #1: To Protect Against Mold
In a humid climate as we have in North Carolina, a vented crawlspace is subject to the key ingredients for mold: high air relative humidity, limited airflow, low light, and moderate to hot air. By properly sealing a crawlspace and adding environmental conditioning (air induction and/or dehumidification), we alleviate those conditions and inhibit mold propagation.
Reason #2: To Improve Indoor Air Quality
Building science studies show that an average of 40% of the air we breath in our homes originates in the crawlspace. An average vented crawlspace has very poor-quality air instigated by mold, mildew, rust, wood rot, deteriorated fiberglass insulation, pest urine/feces/corpses, dust, pathogens, and natural vapors (odors from decaying organic matter in the crawlspace soil). This poor-quality air gets into your living space via stack effect (natural movement of air upwards through a home) and leaks in your crawlspace-installed HVAC ducts and components.
A sealed crawlspace moderates relative humidity which inhibits mold, mildew, rust, and wood rot. Fiberglass insulation, not needed for a sealed crawlspace, is removed and no longer present to be an air quality deterrent. A sealed crawlspace blocks ingress points to keep pests (insects, rodents, snakes, etc) out. A good-quality vapor barrier will guard against odorous vapors. We can further alleviate bad odors by applying a natural deodorization spray comprised of non-pathogenic bacteria and enzymes that are specially designed to consume (not just cover) decaying organic matter.
The hallmark of a well-sealed crawlspace is the elimination of poor-quality air which directly improves indoor air quality in your living space above.
Sealed Crawlspace Option #1: Crawlbarrier®
If your existing fiberglass insulation is in good shape, we can seal the crawlspace with CrawlBarrier®.
We start by installing polyethylene vapor barrier to the crawlspace ground. We install white vapor barrier (options for 10-mil, 10-mil reinforced, 12-mil reinforced, or 16-mil reinforced). All of the vapor barrier options are much stronger than the 6-mil products allowed by building code. We set the vapor in place with heavy-gauge galvanized liner staples, roll fully up at the foundation piers, roll-up at the perimeter walls (will be subsequently sealed to the perimeter walls by the CrawlBarrier®, and we tape the vapor barrier at all foundation piers and panel seams.
We then mechanically fasten CrawlBarrier® to the crawlspace perimeter walls and tape all of the panel seams. The foundation vents are further sealed with foam board and foam spray.
By installing CrawlBarrier® to the crawlspace perimeter walls, we seal the crawlspace from the outside air. We then add a means to condition the residual moisture from the crawlspace with either air induction or a dehumidifier.
Sealed Crawlspace Option #2: Closed-Cell Spray Foam
This option starts with removing and hauling away the existing fiberglass insulation. We then air-seal the subfloor which separates the living space above from the crawlspace by sealing all penetrations with foam spray. New polyethylene vapor barrier (options for 10-mil, 10-mil reinforced, 12-mil reinforced, or 16-mil reinforced) is installed on the crawlspace ground; set it in place with heavy-gauge galvanized liner staples, full roll-ups on the foundation piers, roll-ups on the perimeters walls (will be subsequently sealed sealed to the walls with the Spray Foam), and vapor barrier tape on all foundation piers and panel seams.
We then seal with crawlspace with 2″ closed-cell spray foam applied to the crawlspace exterior wall and rim joists. The still plate and 3″ below the still plate remain exposed for future termite inspections.
Once sealed, we install air induction, a dehumidifier, or a combination of both in order to extract residual air moisture from the crawlspace.
Sealed Crawlspace Option #3: Bora-Foam® Rigid Foam Board
Same initial steps as Option #2 but, instead of applying 2” closed-cell spray foam, we seal the walls with BoraFoam® Rigid Foam Board. BoraFoam® is 2.5″ thick and set into the crawlspace exterior wall with concrete anchors, the seams taped with vapor barrier tape, and the edges sealed with foam spray. We further install the BoraFoam® onto the rim joists, sealed with foam spray. The still plate and 3″ below the still plate remains exposed for future termite inspections.
BoraFoam® is pretreated with Borate, an anti-termite additive. It also comes pre-laminated with 3-mil polyethylene vapor barrier attached on each side (6-mil accumulative).
Bora-Foam® provides a cleaner appearance that Spray Foam, as Spray Foam expands unevenly when applied.
Being a cured foam board, there is no off-gassing in the crawlspace during installation. For homeowners sensitive to chemicals being used in/around their home, this is a substantive benefit of this Option.