The crawl space is sealed, or it is vented
“The crawl space was encapsulated a few years ago — does that cover it?”
Encapsulation for moisture and a membrane for soil-gas depressurization are related but not the same job. A moisture barrier can be well installed and still not be sealed to the standard a depressurization system needs.
A vented crawl space is a different situation again: ventilation dilutes the crawl space itself but may do little for the floor above, depending on how the two connect.
Why this matters
What it changes about the decision in front of you.
- Depressurization requires a surface that can hold a pressure difference, which means sealed seams, sealed edges, and sealed penetrations.
- A vented space still communicates with the house through floor penetrations and ductwork, so venting is not a barrier.
What it could influence
Where the effect is likely to show, and in which direction where that is knowable.
- An existing membrane may be adaptable, which can reduce scope, or may need replacing.
- Whether the vents stay open or are closed affects both moisture and the pressure relationship.
What this does not settle
What still stands. Noticing a problem is not the same as losing the evidence.
- An existing encapsulation is not wasted work — it is frequently a good starting point.
- A sealed crawl space does not establish that levels above are low.
- It does not follow that encapsulation must be redone; that depends on the detailing.
What a professional is likely to ask
Worth having answers ready. None of these is a test you can fail.
- Who installed the membrane, to what specification, and whether seams and edges were sealed.
- Whether penetrations through the membrane were detailed.
- Whether the vents are open, closed, or sealed.
What you can check yourself
Things you can establish today, without anyone visiting.
- Whether a membrane is present and whether seams are taped.
- Whether it runs up the walls or stops at the floor.
- Whether the vents are open.
What genuinely needs somebody on site
Where this platform stops. These are not questions a website can answer about your house.
- Whether the membrane will hold a pressure difference, which is a test rather than an inspection.
- The condition of the seal at edges and penetrations, much of which is not visible.
Categories a next step could fall into
Unordered, and none of them is a recommendation. Which applies depends on things this page does not know about your situation.
Related reading
- Crawlspace mitigation — A crawl space is mitigated by sealing a membrane over the soil and drawing air from beneath it — more labour than a slab, and a common source of quote differences.
- Cost drivers — Seven variables that explain nearly every price difference.
Sources
- U.S. EPA — Consumer’s Guide to Radon Reduction
When you are ready to talk to somebody
Tell us about your home and what you are trying to work out. We will tell you honestly whether we can route it to a provider in your area today.