Madison County has been one of the fastest-growing parts of Alabama, and new subdivisions keep filling in around Madison, Harvest, Meridianville, Owens Cross Roads, and the edges of Hampton Cove. If you're building a house, or buying one before the slab is poured, you have the cheapest opportunity you'll ever get to deal with radon. The EPA calls the approach radon-resistant new construction, or RRNC. This guide explains what it involves, how it fits Huntsville building practices, and what to ask your builder.
Why it matters in a Zone 1 county
Madison County is in Zone 1 on the EPA Map of Radon Zones, the highest-potential category, and the Alabama Department of Public Health lists it among the state's highest-potential counties. Radon comes from uranium in the soil and rock under the house, so the age of the house doesn't protect it. Modern, tightly built homes can actually hold radon in more effectively than drafty old ones.
Adding a mitigation system to a finished house means coring the slab, running pipe through finished closets, and working around ductwork and plumbing. Putting the main parts in during construction is simpler, because most of them go under the slab before the concrete is placed.
The building blocks of RRNC
The EPA describes a short list of features that work together.
A gas-permeable layer
Usually about 4 inches of clean, coarse gravel under the slab, or a soil-gas collection mat. Soil gas can move freely through it to a single collection point instead of pushing up through cracks.
Plastic sheeting
Polyethylene sheeting on top of the gravel, under the slab. Builders often install a vapor retarder here anyway for moisture; for radon, the seams and penetrations matter, so ask that they be lapped and sealed.
Sealing
Caulking and sealing of slab joints, cracks, and every pipe or conduit that comes up through the floor, so soil gas doesn't take shortcuts into the house.
A vent pipe
A 3- or 4-inch PVC pipe that starts in the gravel layer, runs up through the house, usually inside an interior wall, and exits above the roof. Without a fan, this is a passive system.
An electrical box in the attic
An outlet near the vent pipe so a fan can be added later. This small step is what turns a future fix from a project into a quick service visit.
Huntsville building details worth asking about
Slab-on-grade and post-tension slabs. Many new homes in the area are built on slabs, and some use post-tensioned concrete. Coring a post-tension slab later means locating the steel tendons first. Installing the suction point and riser before the pour avoids that problem.
Crawl spaces and stem walls. Some custom and hillside homes are built over crawl spaces. The RRNC version is a sealed membrane over the soil with a pipe connection under it. See our crawl space page for how those systems work after the fact.
Basements on sloped lots. Walkout basements around Monte Sano and Hampton Cove put a lot of below-grade wall in contact with soil. Ask how wall-floor joints and any sump will be sealed.
Passive or active?
A passive system often lowers radon, but it's not designed to guarantee a result. An active system adds the fan from day one. A practical approach many buyers take is to require the passive rough-in, then test after moving in. If the result is 4 pCi/L or higher, a certified mitigator adds the fan. Many homeowners also choose to add it between 2 and 4 pCi/L, the range where the EPA says to consider a fix.
Codes and contracts
There is no statewide Alabama law requiring radon-resistant construction. The International Residential Code includes a radon control appendix, but it applies only where a local jurisdiction adopts it. Don't assume your house will get these features automatically. Ask your builder directly, in writing, before the foundation goes in, and put what they agree to into the contract.
Questions to ask your builder
- Will there be a gravel layer or soil-gas mat under the slab, with sealed plastic sheeting over it?
- Will you install a vent pipe from the gravel layer through the roof, and where will it run?
- Will there be an outlet in the attic next to the pipe for a future fan?
- Will slab penetrations and joints be sealed?
- If the slab is post-tensioned, where will the suction point be placed?
- Will the pipe be labeled as a radon system?
- Can I test before closing, and will you activate the system if the result is high?
Testing the finished house
RRNC reduces the odds of a high reading; it doesn't replace a test. Test after the home is finished and the HVAC is running normally, then consider a long-term test through the first winter. Our radon testing page explains the options. If the house is already built without these features, a standard mitigation system can still be retrofitted, and our cost guide shows what drives the price.
Frequently asked questions
Do new homes in Huntsville need radon testing?
Yes. A new house can test high just like an old one, and Madison County is EPA Zone 1. The EPA recommends testing every home, including new ones built with radon-resistant features.
Does Alabama require builders to install radon systems?
Not statewide. The International Residential Code includes an optional radon control appendix that applies only where a local government adopts it. Ask your builder and the local building department what applies to your lot.
What is a passive radon system?
A vent pipe that runs from a gravel layer under the slab, or from beneath a crawl space membrane, up through the house and out the roof, with no fan. It relies on natural draft and often reduces radon, but not always enough.
Can a fan be added later?
Yes, if the builder roughed in the pipe and left an electrical outlet in the attic near it. Adding a fan to an existing passive pipe is usually a quick job for a certified mitigator.
Can a post-tension slab be cored for radon?
Only with care. Post-tension slabs contain steel cables under high tension. A mitigator must locate the tendons before drilling, which is one more reason to put the suction point in during construction.