What about my crawl space?

Why a crawl space is different from a full basement

In a poured-concrete basement, the slab is the boundary. The mitigation system pulls on the gravel below the slab and the slab itself becomes the seal. In a crawl space, there is no slab. The boundary has to be built. That is what the vapor barrier does.

Crawl spaces also tend to communicate with the rest of the house more openly than a finished basement does. Air moves up into the floor system, into wall cavities, and into the living space above. Without a sealed barrier, the radon picture in a crawl-space home is shaped almost as much by what is happening in the crawl as by what is happening below it.

How the install works

1. We pre-test to confirm the current radon level in the lowest living area.
2. We clean out the crawl space and check the existing floor (dirt, gravel, or thin concrete) and the walls (block, poured, stone, or a mix).
3. A 12- or 20-mil reinforced vapor barrier goes down. Seams are overlapped and sealed with seam tape. The edges run up the walls and seal with a mechanical fastener or a specialized adhesive.
4. A radon pipe ties into a suction point under the barrier, runs up through the rim joist or out a sidewall, and vents above the roofline (or out the side wall if local code allows).
5. An inline radon fan pulls on the pipe, with a manometer gauge mounted where the homeowner can see it.
6. We post-test, ideally with a continuous monitor, to confirm the number dropped below the EPA action level.

Where this comes up in our service area

Crawl spaces are more common in the older rural housing south and east of Rochester than in the city itself. We work crawl-space homes regularly around:

• Oronoco lake-side and rural acreage homes.
• Stewartville historic central blocks.
• Chatfield township homes outside the city core.
• Preston and the surrounding Root River bluff country.

Homes with a partial crawl plus a partial basement (common in renovations and additions across the region) need both approaches. The basement portion gets a standard sub-slab suction system. The crawl portion gets a sub-membrane system. The two can run on one fan if the geometry allows, or two fans if not.

The moisture side-benefit

A sealed crawl space is a dry crawl space, more often than not. The vapor barrier blocks ground moisture and the fan continuously pulls humid soil air out. We hear from homeowners after install that the crawl space smells different, that the floor above feels warmer, and that the rim joist insulation no longer stays wet.

The system is built for radon. The moisture improvement is real but is not the design goal. If the crawl space has active water intrusion (standing water, springs, or a failing exterior drain), that needs its own fix.

What changes the answer

• Crawl space height. A 36-inch crawl is easy to work in. A 18-inch crawl is harder and slower.
• Existing floor. Dirt or gravel takes a heavier-duty barrier and more sealing. Old thin concrete may be best left in place under the barrier.
• Wall construction. Block walls take different sealing than poured walls. Stone walls (common in pre-war homes) take careful work.
• Access. A crawl space accessed only through an exterior hatch is a longer visit than one with a basement door.
• HVAC ducts in the crawl. Common, and they affect how air moves above and below the barrier. We plan around them.