Radon Preventive Measures for New Homes

Radon Preventive Measures for New Homes
It is very difficult to predict before construction whether a new home will have high radon levels. Fortunately, preventive measures can be taken by your builder during the design and construction process.

Most of these measures are low-cost, desirable for other benefits they provide, and difficult to install after the home is constructed. They include:

• minimizing potential entry routes for radon
• reducing forces that draw radon into a home
• making provision for an active soil depressurization system.

Many elements of these measures are a requirement of the 2005 National Building Code of Canada (NBC) issued by the National Research Council of Canada. Check with your builder whether your local authority with jurisdiction for building codes has adopted and enforces the NBC’s soil gas control requirements. If not, make sure these measures are included in the plans and specifications for your new home.

Minimize Potential Entry Routes for Radon
The entry routes for radon in new construction are similar to those discussed for existing homes. Methods your builder can use to reduce entry routes in a new home include:

Minimize cracking of the basement floor slab by:

• Properly preparing the sub-slab area (i.e., replace unstable soil, large stones, etc.)
• Using higher strength concrete. For basement floors, concrete with a 28-day minimum compressive strength of 20 Mpa (3000 psi) is recommended.
• Using additives in the concrete called “plasticizers” to improve the workability of the concrete. If a plasticizer is not used, there is a likelihood that water will be added on-site to produce more workable concrete. Adding water to the concrete will lower its strength and increase its tendency to crack.
• Providing proper curing conditions. Moistening the slab or coating it with a special compound during curing will result in stronger, more durable concrete. Also if the weather is hot and dry or below freezing, your contractor must take appropriate precautions.

Use control joints in the concrete floor slab. Since some cracks in the basement slab may be unavoidable, your contractor can direct cracks into controlled locations where they can be sealed with polyurethane caulking. Control joints can be created by:

• casting plastic special “Ts” into the slab; or using a trowel before the concrete has set; or  saw-cutting the slab within one day of its being poured.
• Seal the basement floor/foundation wall crack. There are several options for sealing this potential radon entry point. Note that proper preparation of surfaces to be caulked is critical to obtain an effective, long-lasting seal.
• Seal around all penetrations of the foundation walls and basement floors by objects such as utility lines (e.g., water, sewer, electrical, natural gas, fuel oil). The center of hollow objects that penetrate the walls or floors (e.g., metal support posts or masonry for fireplaces) should also be sealed or blocked.
• Install a barrier of at least 0.15 mm (6 mil) polyethylene under the basement floor slab or on top of exposed soil in crawl spaces (see figure 17, page 27). Joints in the polyethylene should be overlapped no less than 300 mm (12 in.). In crawlspaces, seal the joints and edges with acoustical sealant. Look for products that are a more durable alternative to regular polyethylene, such as cross-laminated polyethylene.
• Install special traps in floor drains that allow water to drain but prevent radon from entering the basement. These traps have the added benefit of keeping out molds, odours, insects and cold drafts. However, they are not a substitute for a sewer backup valve.
• Use a sealed lid on the sump. Your builder may either purchase a sealed unit or field fabricate a sealed lid. A sealed lid keeps out radon as well as molds, odours, insects and cold drafts. It also reduces the risk of injury to small children.
• Use a solid course of masonry units at the top and bottom of concrete block foundation walls. If regular concrete blocks with voids are used instead, a major entry route for radon may be created.

Reduce Forces That Draw Radon into a Home
Reducing the pressure difference between the home and soil may reduce the amount of radon drawn indoors. Options include:

• Choose a direct-vent gas or oil furnace, boiler or water heater rather than a conventionally vented unit. Besides reducing the negative pressure in a home, direct-vent combustion appliances reduce energy costs and are less prone to spill combustion products into the home.
• Choose a wood or gas fireplace that is equipped with glass doors that fit tightly, if installing a fireplace. Gas fireplaces should be direct-vent.
• Install a balanced ventilation system, such as a heat recovery ventilator (HRV). A balanced system relies on both supply and exhaust fans to provide ventilation. An HRV will reduce the energy penalty associated with providing more ventilation to a home.
• Never install ducts for a forced-air heating or ventilation system in the basement floor slab. If a crack develops in the slab between the soil and ductwork, radon could be drawn into the home.
• Pay extra attention to ensure that the air barrier (especially between the house and attic) is well-sealed. This will reduce the effects of weather, which can depressurize the home. A well-sealed air barrier will also reduce heating costs and minimize hidden moisture damage to the structure of the home.

Make Provisions for Active Soil Depressurization
The radon prevention methods listed in this section may not always be sufficient to achieve low annual average radon levels – 200 Bq/m3 (5.4 pCi/L) or less. As a result, consider making provisions for an active soil depressurization system.
It is more practical and less expensive to install the following components of an active soil depressurization system during, rather than after, construction of your new home.

• Before pouring a slab, ensure that the entire sub-slab area is filled with at least 100 mm (4 in.) of coarse gravel.
• Install a polyethylene air barrier.
• A short length of PVC pipe of at least 100 mm (4 in.) diameter should be cast into the floor slab. The pipe should be capped and labeled so that it is not left open.
• After the home is built and occupied, measure the radon levels. If the levels exceed the guidelines given in this booklet, uncap the pipe, install an exhaust fan, and vent to the outdoors. The U.S. EPA recommends exhausting the fan at the roof. The fan should be designed for continuous operation in high humidity environments – in-line fans suitable for radon reduction systems are available from heating, ventilation and air-conditioning wholesalers. This system will ventilate the sub-slab area and should result in significant reduction of the radon levels. Retesting to confirm this is recommended.

Although it is preferable to locate the fan outside the living space, this may not be practical in very cold climates. An alarm to warn the occupants if the airflow in the system is restricted or blocked is a wise addition. Also, parts of the system which run outside or through unheated attic space will have to be insulated to reduce condensation and blockage by frost or the buildup of ice.

Contact your REALTOR at Coldwell Banker Vantage Realty for more tips and advice on what you can do if you have concerns of Radon in your home.

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