Crawl space radon mitigation in Duluth, MN

Why crawl spaces are different

Under a basement, a concrete slab creates a natural barrier, and a fan can pull from beneath it. A dirt or gravel crawl space has no such barrier, so the contractor has to create one.

Many Duluth homes have additions or sections with different foundations. A house can have a full basement with a crawl space under a back room or a later addition. If only the basement is treated, the crawl can keep feeding radon into the home, so all the foundation areas need to be planned together.

How a sub-membrane system works

This approach, called sub-membrane depressurization, is EPA's preferred method for crawl spaces. It is the same idea as a sub-slab system, with heavy plastic standing in for the concrete:

• The ground is cleared of debris and sharp objects that could puncture the sheeting.
• Heavy-duty polyethylene is laid across the floor, overlapped, and sealed at seams, walls and piers.
• A perforated pipe or suction point is installed beneath the membrane.
• The pipe runs to a continuously operating fan, then vents above the roofline.
• A gauge is added so you can confirm the system is working, and a follow-up test confirms the result.

Other options, and why they are second choice

Ventilating the crawl space can lower radon by bringing in outside air, sometimes with a fan. But the effect is often less dependable, and the cold air can freeze pipes and raise heating bills, which is a real concern in a Duluth winter. Sealing the floor above the crawl helps slightly at best. For most homes with a real radon problem, a contractor will recommend a membrane system instead.

Before the crew arrives

A crawl space install goes faster and better when the space is ready. Remove stored items, or tell the contractor which ones have to stay. Point out any wiring, ductwork or plumbing that runs low, and any access hatch that is hard to reach. If there are animal droppings, standing water, mold or loose insulation on the ground, mention them when you ask for a quote, because they may need attention first and can change the price.

Duluth's cold matters here, too. Pipes in a vented crawl space may already be vulnerable to freezing, so ask how the job will affect the airflow and temperature of the space. Sealing a membrane does not by itself make a crawl space warm, and if you are also planning to insulate or encapsulate the crawl, it is cheaper to plan the two jobs together.

Once the membrane is down, try not to walk on it unless you have to, and keep sharp objects off it. Tears let soil gas through and reduce suction. Check the seams when you are down there for any other reason, and repair punctures with the tape that the contractor recommends.

What to ask before you hire

A crawl space job has more ways to differ from one quote to the next, so ask:

• How thick is the membrane, and how are the seams and edges sealed?
• How will the crew get in, and is the space tall enough to work in safely?
• Will any wet spots, mold or standing water need attention first?
• Does any part of the floor, such as a basement section, need its own suction point?
• Can you walk on the membrane to reach pipes or wiring later, and how are punctures repaired?
• What is the contractor's Minnesota radon license number?

What to test

MDH says real estate tests should be done in the lowest occupiable level of each foundation type, including a room above a crawl space. If your home has both a basement and a crawl space section, tell the tester how many foundations there are so that they bring enough devices.

Common questions