Tallying up the costs, a fail-safe radon mitigation system involves an extra 2 inches of coarse gravel under the slab (assuming you already place 2-inches of course aggregate or sand under your flatwork), costing about $150; an extra roll of drain tile, $75; a roll of 6-mil plastic (again, something you might be doing already), $25; and about 24 feet of 4-inch PVC drain pipe (for a two-story house), topping out your costs with another $50 to a sum of $300.
If you're cheap, like me, then you could build a system for less (I'll tell you how at the end of this article) but on the Concept House we felt a national demonstration project required a first-rate installation.
The basics of good systems are, well, very basic: Under the slab of your house, you'll need porous material that allows gas (and water vapor) to dissipate. This means 4 inches of gravel (2-inches more than the usual 2-to-3-inches of gravel required for good practice under any concrete slab). Next, add a means to catch and vent the gasses so they do not leach into the interior of the house. We accomplished this at the Concept House by installing a 15' by 20' square of silt-screen warped, flat drain tile connected to a 4-inch tee fitting. Eventually this fitting will attach to a 4-inch riser venting out of the attic like a plumbing vent.
After the drain tile was in place and connected to the tee, we placed a carefully sealed vapor barrier over the gravel. The typical barrier consists of inexpensive polyurethane, but we used a tough Cosella Dorken waterproofing membrane because it was donated to the project. The advantage of this deluxe membrane came while placing concrete over its tough, corrugated plastic surface; it was strong enough to handle work boots and wheelbarrows without ripping. A little TLC can accomplish the same ends with poly.
After the vapor barrier went in, all that was left was to pour the slab and then, once the concrete had set, carefully seal the perimeter between slab and basement wall with caulk, and seal the sump pit (called crock pot in some places) with a caulked-in-place Plexiglas cover that allows a homeowner to see when water is building up in the pit.
At top-out, the plumber attached a 4-inch vent pipe to our radon tee and ran the pipe through the house and outdoors, like a plumbing stack. Voilá, we were now breathing clean, radon-free air. Should radon levels still prove too high, it's easy to convert a passive system to an active by simply installing an inline fan that generates negative pressure, forcing the poisons gas up ad away from family, friends and your homebuyer.
Okay, I promised a cheapskate solution: 4 inches of gravel under the slab (or crawl space); one perforated 4-inch tee (you can buy one at the home improvement center for pennies); and a layer of 6-mill poly under the slab (or crawl space). Use duct tape to seal the seams. Caulk the edges of your slab and any control joints. You could now cap the system and test the house. If it does not exceed the radon standard, you're done and will have a dry, comfortable basement, slab house or crawlspace. If it does not test within the EPA's safety guidelines, then simply vent through the roof for a cheap and healthy way to keep your customers (or you) alive and breathing easy for the good years ahead!
Fernando Pagés Ruiz is president of Brighton Construction Co. Inc. in Lincoln, Neb., and a consultant on affordable housing. A 30-year veteran of the construction industry, he is the author of Building an Affordable House: Trade Secrets to High-Value, Low-Cost Construction and Affordable Remodel, both published by Taunton Press. E-mail him at fpages@buildaffordable.com.
