What is crawl space encapsulation? 10 things you should know before you begin!

Posted on: January 9th, 2013 by

As a Crawl Space Encapsulation contractor we verify that crawl space encapsulation is the correct application as it is NOT a total solution for every crawl space. Below are 10 considerations to take into account for each individual crawl space.

1)      High Humidity Levels? (Look for water leaks, ground water, normally high relative humidity because of vented crawl space.)

2)      Unsealed mechanicals in crawl space? (This can effectively suck unhealthy crawl space air into return ducts and redistribute to living areas.)

3)      Dirt or gravel floor? (Humidity levels from 50% to 90% are easily found in dirt/gravel crawl spaces, 55% is enough to support the growth of harmful Black Mold, fungi, and microorganisms.)

4)      Vents in crawl space? (Vented crawl spaces allow relative humidity levels from outdoors to add to already high humidity levels in a crawl space leading to growth of mold, fungi, and other microorganisms. This air also carries dust, pollen, and other allergens.)

5)      Poorly installed plastic vapor barrier? (A sheet of plastic lying on the ground is not enough to keep ground moisture from entering the crawl space. Standard plastics are not sealed at the seams or perimeter walls, they develop dry rot, and are not strong enough to withstand foot/crawl traffic.)

6)      Is the crawl space conditioned? (The crawl space should be conditioned like any other room in the house, you don’t leave your basement windows open in the winter, and your crawl space is no different. A dehumidifier may still be needed after encapsulation to keep the relative humidity below 50%)

7)      Rodent issues? (If your crawlspace is infested by rodents, no thickness of liner material will stand up to the jaws of burrowing rodents.)

8)      Falling, wet, and moist fiberglass insulation? (Fiberglass insulation becomes heavy from the relative humidity and will fall to the moist ground where it becomes be a haven for mold, mildew, fungi, and other microorganism growth.)

9)      Hydrostatic pressure? (Is there is a high water table or water that is hydrostatically forced from the ground or crawl space walls? The introduction of a perimeter drain tile system with a sump pump may be required.)

10)   The “Stack Effect”? (When warm air rises and escapes from your living area it creates negative pressure and causes a sucking effect to replace the displaced amount of air. A typical crawl space can contribute up to 40% of the air replaced by the stack effect.)

Before we start a crawl space encapsulation, we do a ground up inspection of the existing conditions. We’ll evaluate the crawl space for higher than normal humidity levels and determine if a drain tile system is needed. It makes no sense to cover up a water issue without addressing the cause. Additionally, we’ll look for mechanicals that may be adding humidity to the crawl space; is there an air conditioning unit with faulty drainage, a leaking plumbing pipe, a bathroom with a leaking shower/bath? We will also look for evidence of rodents that may have burrowed under the foundation and into the crawl space. This may call for the introduction of a “Rat Slab” to prohibit their return into a newly encapsulated crawl space.

Looking up the walls, we’ll determine if there are active foundation cracks that may be letting water in by hydrostatic pressure. Are there open vents around the crawl space letting unconditioned air in from the outside?

Looking further up, we’ll determine if the floor joists are sagging or rotten from the exposure to years of high humidity levels. Is there damaged insulation that needs to be removed? Is there mold growth on the underside of the floor sheathing? All of these issues need to be addressed and remedied before any work begins.

If the project is in a frost prone region like Chicago, we recommend insulating the walls with SPF or Spray Polyurethane Foam. The Closed Cell spray foam is air impermeable and a rated vapor barrier. We will lay out a cross woven, puncture resistant, and UV stable plastic membrane over the dirt/gravel floor and lap the ends about a foot up the perimeter walls (these will be spray foamed to the wall later to seal the top seams). Any overlapped seams or penetrations will be sealed with a manufacturer approved seam tape to seal these areas. Any vents will be closed and sealed off permanently. Then spray polyurethane foam is sprayed on the concrete or brick walls and into the joist pockets around the rim joists). The area of the rim joist can account for up to 17% of the heating and cooling cost due to air infiltration. It will also make cold floors above the crawl space disappear.

After the encapsulation is complete, it is a good idea to monitor the crawl space for humidity fluctuations. Sometimes it’s necessary to introduce a vent into the crawl space to regulate humidity and in extreme cases, a dehumidifier may be in order to keep humidity to a minimum.

Houses that are NOT good candidates for crawl space encapsulation include; houses in a flood plane, houses built on piers, mobile homes with a skirting, enclosed porches without a continuous foundation. A good solution for properties described above is spraying closed cell spray polyurethane foam insulation to the underside of the first floor living space and floor joist. This will seal off any moisture/ air infiltration into the living area and be a FEMA approved material in a flood plane.

4 Responses to What is crawl space encapsulation? 10 things you should know before you begin!

  1. basement waterproofing NY had this to say about that:

    Crawl space encapsulation (sealing) is the treatment that building scientists recommend to turn a damp, dirty, moldy crawl space into a clean, dry space where mold can’t grow.

  2. Isabel Marant had this to say about that:

    This product is really amazing, why it isn’t required by building codes across America is silly.

  3. Aide Doll had this to say about that:

    I love this website, it has given me a lot of great information for my upcoming addition and turning our crawl space into a useable area.

  4. Able had this to say about that:

    Informative article, just what I was looking for.