Mitigation for crawls, hillside basements, and the houses in between

A mitigation system is a fan and a path. The fan lowers the pressure under the house so soil gas goes to the roof instead of the hallway. Everything else is details: where the soil is, how many foundations you have, and whether the crawl is a mud room or a clean plastic tub.

We design for Washington County houses, which means we see dirt crawls, walkout basements on a ridge, and additions that turned one house into two soil contacts. We do not sell a one-pipe miracle for a split lot.

What "high" means before we cut

EPA's action level is 4 pCi/L. We still want a real test, not a memory of a kit from 2014. If you're buying, the continuous monitor on the real estate page is the file. If you live here and a TDEC kit came back ugly, we confirm placement and then we talk systems.

Tennessee does not state-license radon mitigators. That is a fact, not a sales pitch. Look for NRPP or NRSB mitigation credentials. Ask who will be on the job. Ask what the post-mitigation test looks like.

Crawl spaces

Most Johnson City and Jonesborough ranches sit on a crawl. The soil is the radon source. The floor is the leak. A proper crawl system is usually:

• A sealed polyethylene membrane over the soil, taped and sealed at the walls and penetrations
• A suction pit or pipe under that plastic
• A fan that pulls continuously
• Exhaust above the roof, away from a window you actually open
• A U-tube manometer so you can see the system is pulling

That is sub-membrane depressurization. It is not a $12 box fan in a foundation vent. Vents move some air on a windy day. They do not hold a pressure field under the house.

If the crawl is wet, we will say so. A radon membrane is not a French drain. Standing water under plastic is a mold story. Fix the water path or at least know you're stacking jobs.

Basements and slabs

A full basement or a slab-on-grade gets sub-slab depressurization. We core the slab, build a small pit in the gravel or soil, and run PVC to a fan. Hollow block walls and a sump pit are extra entry points. Sometimes the sump gets a sealed lid. Sometimes the block needs its own suction. We decide that on site, not from a photo of the street.

Newer Boones Creek and Colonial Heights slabs still need this if the air test is high. Concrete is not a radon shield. It is a lid with joints.

Hillside and split foundations

This is the Tri-Cities specialty. Buffalo Mountain, Indian Ridge, Boones Creek ridges, Bays Mountain, and the South Holston slopes like a walkout basement on the downhill side and a crawl or slab uphill. Those two volumes do not share soil gas. A single suction point can clean one side and leave the other sitting at 8.

We look at both faces. We may run two pipes to one fan, or two fans, or a membrane on the crawl and a slab pit on the walkout. That costs more than a ranch with one dirt rectangle. It also works.

Jonesborough's older stone and brick houses add another wrinkle: fieldstone, dirt floors, and chimneys that were never detailed for a plastic tub. We can still mitigate them. We will not pretend it's a 2008 spec home.

What a job costs and what you get

National and East Tennessee mitigation work often lands somewhere between $800 and $2,500 for a straightforward ranch, and more when the foundation is split, the crawl is a maze, or the discharge path is ugly. That is a market range, not a bid. Request a quote with the town, the foundation, and the test number if you have one.

A finished job should include:

• A running fan and a visible manometer
• A label on the system
• A post-mitigation test after the house has settled
• A plain explanation of what to watch (fan noise gone, manometer flat, retest after a remodel)

Fans last years, not forever. When it dies, the house does not become immune. Replace the fan. Retest.

What we will not do

We will not promise a number before we see the foundation. We will not treat a Zone 1 map as a design document. We will not skip the post-test. We will not tell you a bathroom fan in the crawl is "pretty much the same thing."

If you want the geology lecture, it's on the Washington County page. If you want the system, send the quote form.