How can I mitigate radon in an older house with no access to the crawl space?

You fix it from outside the crawl space. A radon mitigation system pulls air from under the floor or under a sealed membrane and vents it above the roofline, so we do not need to crawl all the way under the house to make it work. Radon mitigation runs $900 to $6,000, and most homes land around $1,950 to $2,250, and a radon test before that runs $50, credited toward the job if you move ahead.

Here is what is going on. Radon is a gas that seeps up out of the ground. Old New England houses sit on dirt or fieldstone crawl spaces, and that bare earth lets the gas right in. Tight access does not change the gas. It just changes how we route the system.

For a dirt or fieldstone crawl, the standard fix is sub-membrane depressurization. We lay a sealed vapor membrane over the dirt, seal the edges, then put a fan and a vent pipe under that membrane. The fan creates light suction beneath the membrane and carries the radon up a pipe and out above the roof. The gas never gets a chance to reach your living space. We do install these.

Most of the work happens at the membrane edges and at the pipe. We do not need to belly-crawl every square foot. We need enough room to seal the perimeter and tie in the suction point. If the hatch is tiny or buried, we figure out the route on the free inspection. Every old house is different. We look first, then tell you the plan.

If your house has a poured slab instead of a dirt crawl, the fix is sub-slab depressurization. Same idea. A pipe and a fan pull radon from under the concrete and send it up and out. You do not need crawl access at all for that one.

The layout drives the cost. A simple straight pipe run to the roof costs less than a system that has to wind around finished rooms. A dirt crawl needs the membrane, so it usually runs more than a clean slab job. The fan, the pipe length, and how hard the vent route is all move the number. We give you the figure after we see it. Radon mitigation runs $900 to $6,000, and most homes land around $1,950 to $2,250.

You may not need a full system yet. The EPA sets the action level at 4.0 pCi/L. Below that, between 2 and 4, the EPA says you may want to consider fixing it (EPA). So test first. A radon test runs $50, credited toward the job if you move ahead. If your number comes back low, you can wait and watch. We will tell you that. We are not going to sell you a fan you do not need.

Radon is a gas, not a water problem. If your crawl is also damp or muddy, that is a separate fix called crawlspace encapsulation, and it uses a 12-mil wall vapor barrier and a 20-mil floor vapor barrier with drainage matting underneath. Some homeowners do both at once because the membrane work overlaps. But they are two different jobs. Read more on the crawl space services page.

New Hampshire has high radon ground levels in a lot of towns. NH DHHS runs a radon program and recommends every home test, no matter the age (NH DHHS). Older houses with dirt crawls are some of the most common ones we fix.

Our radon work carries a 10-year warranty. We do not guarantee a specific radon number unless we put that in writing. After the system goes in, retesting is your job to confirm the level dropped.

Our radon lead is Branden, who the crew calls “B-Radon.” He is state radon certified (RMS-113966). We are licensed and insured, BBB A+ accredited, and trusted by 5,000+ homeowners across New England with a 4.9 Google rating over 250 reviews.

Want it looked at? Call us at 603-610-1770 or book your free inspection. We send a quote within 24 hours. See how we stand behind the work on the 603 guarantee, and learn more about systems on the radon mitigation page.

Related questions

Can radon get in through a crawl space with a dirt floor? Yes. Bare dirt is the most common radon entry point in old houses. The gas rises straight out of the soil. A sealed membrane plus a sub-membrane fan stops it. That work runs $900 to $6,000, and most homes land around $1,950 to $2,250.

Do I have to test before you install a system? Test first. The EPA action level is 4.0 pCi/L, and a test tells us if you even need a system. A radon test runs $50, credited toward the job if you move ahead. If your number is low, we will tell you to wait.

Is radon a water problem too? No. Radon is a gas. Water in a crawl is a separate fix called crawlspace encapsulation. Sometimes we do both because the membrane work overlaps, but they are priced and warrantied on their own.

How long does a radon system last? The fan and pipe are built to run for years, and our radon work carries a 10-year warranty. Batteries and add-ons are not part of that. We put any specific promise in writing.