Crawlspaces play by different radon rules
A home over open soil needs a different approach than a slab. The foundation type decides the method.
Sealing the dirt instead of drilling the slab
Standard radon mitigation pulls air from under a concrete slab. A dirt-floor crawlspace breaks that plan. There’s no slab to pull under, just open soil breathing gas straight up into the house.
The industry design for that situation is sub-membrane depressurization. Heavy plastic sheeting goes down over the entire exposed floor, seams overlapped and sealed, edges sealed to the foundation walls. A suction pipe slips beneath the membrane, ties into a fan, and vents above the roofline — same principle as a slab system, except the crew builds the “slab” out of plastic first. (The full anatomy of these systems is drawn out in how radon mitigation works.)
Around Harrisburg, true full-crawlspace homes are the minority. This is basement country, thanks to frost depth and a century of local building habit. Where crawlspaces show up is at the edges: older farmhouses on the fringes of Dauphin and Cumberland counties, cottages near the river, and above all, additions. A 1950s ranch that grew a family room in 1978 very often grew a crawlspace under it.
Crawlspaces take more of the method than slabs do. More surface to seal, more penetrations to work around, more time on knees in a tight space. That’s not a complaint. It’s why the assessment matters more here than anywhere.
Where this approach fits
Two kinds of homes typically land on membrane work.
The first is the house entirely over a crawlspace, common in some eras of cottage and farmhouse construction. There, the membrane system is the whole fix.
The second is more common locally: the combined foundation. Basement under the original house, crawlspace under the addition, maybe a slab under the garage. Radon doesn’t respect those boundaries, and in plenty of combined homes the crawlspace section is the main pathway even though everyone’s attention goes to the basement. Those jobs often pair a membrane over the crawl with suction on the slab side, run as one system.
Which combination a house needs is a design question, and it starts from the foundation up. What mitigation involves is the hub for the whole design conversation, whatever your foundation turns out to be.
When it isn’t the fit
Honesty section. A membrane isn’t the automatic answer just because a crawlspace exists.
Some combined foundations test fine once the basement slab gets standard suction; the crawl was never the pathway. Some crawlspaces are too tight, too wet, or too obstructed for a membrane to seal properly until other work happens first. And a few homes with rat-slab or paved crawls can take conventional suction without any membrane at all.
There’s no way to know which case is yours from a webpage, and any contractor who promises a method before crawling the crawlspace is guessing on your dime. The sequence that works is the boring one: look first, design second, and verify the result with a test at the end. The assessment is where it starts.
Crawlspace under the house? Start with the assessment.
Frequently Asked Questions
Does a crawlspace home really need a different system?
Yes, when the crawlspace has exposed soil. Sub-slab suction needs a slab to pull under, and a dirt crawlspace doesn't have one. The industry answer is a sealed membrane over the soil with suction beneath it, so the gas gets collected before it reaches the air your house breathes.
What does the membrane involve?
Heavy plastic sheeting laid across the crawlspace floor, overlapped, run up the walls, and sealed at seams and edges. A suction pipe pulls from underneath the membrane and ties into a fan and vent run. Done well, it turns loose dirt into something the system can actually draw against.
We had the crawlspace encapsulated. Doesn't that cover radon?
Not by itself. Moisture encapsulation and radon work look similar but aim at different problems, and a liner without active suction can still let radon through gaps and penetrations. If radon is the concern, the question is whether there's a fan pulling from under the liner, and whether a test afterward verified the level.
Do you have to crawl the whole thing?
The honest answer is that somebody has to look. Membrane work depends on access, clearance, and what's living down there: ducts, piping, debris, old vapor barrier. That's why crawlspace jobs get scoped after an assessment, not priced off a phone description.