If you live in an older Murfreesboro neighborhood, or in one of the many Rutherford County subdivisions built over the last few decades, there's a good chance your house sits over a crawl space. It's one of the most common foundation types in Middle Tennessee. Crawl spaces are also a direct route for radon, because the soil under them is exposed. This page covers the fix most certified mitigators use and how it fits with the moisture work many local crawl spaces already need.
How radon gets from a crawl space into the house
The bare dirt or gravel floor of a crawl space releases soil gas all the time. Air from the crawl space rises into the house through:
- Gaps around plumbing, drains, and wiring that pass through the subfloor.
- Leaky HVAC ducts, especially return ducts, that run through the crawl space and pull air into the system.
- The subfloor itself, through seams and around floor registers.
- Chases and openings around tubs and showers.
In winter the stack effect pulls harder. In summer, if the HVAC air handler is in the crawl space, as it often is in Middle Tennessee, leaky ductwork can circulate crawl space air through the house.
The proven fix: sub-membrane depressurization
Certified mitigators typically use sub-membrane depressurization (SMD):
- Clear and prep the floor. Remove debris and sharp objects, and grade any high spots.
- Lay a heavy membrane. A thick polyethylene sheet covers the soil. Seams overlap and get sealed, and the edges are fastened and sealed to the foundation walls and piers.
- Add suction. Perforated pipe or a suction mat goes under the membrane and connects to a PVC riser.
- Install the fan. The riser runs out of the crawl space to a fan in the attic, the garage, or on an exterior wall, never in the crawl space or living space.
- Vent above the roof. The discharge clears the roofline and stays away from windows.
- Seal and test. Accessible penetrations are sealed, a manometer is installed, and a post-mitigation radon test confirms the result.
Because suction sits beneath sealed plastic, radon is captured at the soil before it reaches the crawl space air. That's why SMD outperforms simple ventilation.
Talk it through with a certified pro. Free referral for Murfreesboro and Rutherford County homes.
(629) 201-4576Encapsulation and radon: related, not the same
Murfreesboro homeowners hear "crawl space encapsulation" a lot, usually from moisture and foundation companies. It's worth separating the two goals:
- Encapsulation is about moisture. It typically means a liner on the floor and up the walls, closed vents, and a dehumidifier or conditioned air. It can help with musty odors, humidity, and wood rot.
- Radon mitigation adds active suction under the liner. Without suction, sealing a crawl space may reduce outside air dilution, so radon in the crawl space and the house above can actually rise.
The two work well together. If you're getting an encapsulation quote, ask whether it can include a sub-membrane radon port and fan, and test radon after any crawl space sealing job.
Common Middle Tennessee wrinkles
- Low clearance. Some crawl spaces have only a foot or two of headroom. This slows the work but rarely makes it impossible.
- Rock and clay. Limestone outcrops and red clay are common in Rutherford County soils. Membrane installers work around rock ledges and seal to them.
- Standing water. If the crawl space floods, fix the drainage, through grading, gutters, or a sump, before or alongside the radon work.
- Mixed foundations. A crawl space under the main house plus a slab under the garage, bonus room, or sunroom may need two suction points tied to one fan.
- HVAC in the crawl space. Duct sealing is a sensible add-on that helps both comfort and radon.
What does it cost?
Crawl space radon systems are priced by size, clearance, and complexity. As a national reference only, Angi's 2026 data puts typical active radon mitigation systems at about $805 to $1,326, with larger homes and full crawl space membranes costing more. Full moisture encapsulation is a separate and generally larger project. Each local professional quotes your home after an inspection.
Talk it through with a certified pro. Free referral for Murfreesboro and Rutherford County homes.
(629) 201-4576Questions to ask
- What membrane thickness do you use, and how are seams and walls sealed?
- Where will the pipe exit the crawl space, and where will the fan go?
- Do you recommend keeping vents open or closed after installation?
- Can radon suction be combined with my moisture or encapsulation plan?
- What reduction will you guarantee, and how will we verify it?
- Are you NRPP or NRSB certified? Tennessee doesn't license radon contractors, so certification is the key credential.
Haven't tested yet?
Order Tennessee's free kit or book a professional test first. See radon testing in Murfreesboro. Test in a main-floor room, not in the crawl space itself.
Middle Tennessee climate and crawl spaces
Middle Tennessee's long, humid summers are a major reason crawl space moisture problems are so common here, and why so many homeowners are already talking to encapsulation companies. Winter matters, too: when the heat runs, the stack effect pulls more crawl space air into the house. A radon system that captures soil gas under a sealed membrane works through both seasons, while open vents help only some of the time.
More crawl space questions
Will the membrane get in the way of plumbing or HVAC repairs?
A good membrane is meant to be crawled on. Technicians should take care, and any tear should be taped and sealed afterward. Ask the installer for patch material.
How many suction points does a crawl space need?
It depends on the size and layout of the crawl space, how well air moves under the membrane, and whether there are separate sections. Larger or divided crawl spaces often need more than one.
Does a crawl space system work on a house with a slab addition?
Yes. Many systems combine a membrane suction point and a slab suction point on one fan.
Talk it through with a certified pro. Free referral for Murfreesboro and Rutherford County homes.
(629) 201-4576