Crawl Space Radon Mitigation in Denver, CO

No Slab Means No Barrier at All

In a house with a concrete basement floor, the gas has to find a crack. In a house over a bare dirt crawlspace, there is nothing between the soil and the underside of your floor but air. Whatever the ground is producing enters the crawl freely, and from there it moves up into the house through every gap in the subfloor, every duct chase, every plumbing penetration and every set of stairs. This is why the crawlspace houses in the older parts of Denver, Wheat Ridge and Golden can read high while looking, from the outside, like the least likely candidates on the street.

Building the Floor That Was Never There

The fix is to install the barrier the house never had. A heavy reinforced membrane goes down over the entire ground surface, seams overlapped and sealed rather than merely lapped, and run up the stem walls and sealed to them so the edge is closed rather than left open where it matters most. A suction point is drawn from beneath the membrane, so the fan depressurizes the soil under the sheet exactly as it would the gravel under a slab. What you end up with is functionally a slab made of plastic, and it performs like one.

Old Stone Walls Change the Job

Around Olde Town Arvada, downtown Golden and the pre-1930s streets in Denver, the crawl is often bounded by rubble or unmortared stone rather than poured concrete. Those walls are porous across their whole height, so the gas is not only coming up from the floor — it is coming through the perimeter as well. That means more sealing, sometimes a parge coat, and occasionally more than one suction point to hold a pressure field across a space that leaks in every direction.

Headroom Is the Real Constraint

Almost nothing about this work is technically difficult. It is awkward. A twenty-inch crawl full of ductwork and cast-iron waste line is slow to sheet properly, and a job that would take three hours in a stand-up basement can take a day. That is also why the space has to be clear before we arrive: stored boxes and debris have to move, and we will tell you exactly what needs shifting rather than turning up and stopping.

Part Crawl, Part Basement

Plenty of metro houses are both, usually because an addition went on decades after the original build. Each area is its own pressure field, they rarely connect under the ground, and a system that treats one will often leave the other unchanged. Sorting that out is what the diagnostic visit is for, and it usually ends with two suction points sharing a single fan and riser. As with any sub-slab system, the work is only finished when the retest says it is.

How long does it take? One to two days depending on headroom, how much of the ground is obstructed by ductwork and piping, and whether the space has to be cleared first.

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