Radon covered: Building and retrofitting to protect against a persistent and deadly gas.

May 23, 2023

What is a contractor’s role when it comes to mitigating radon build-up?

Across Canada, all homes have some concentration of radon gas within them. The amount differs based on the amount of uranium present in underlying rock and soil, but even houses that are right next to each other can have different concentrations of radon present within them, typically in the basement or ground floor.

Radon is a pervasive issue in Canada as numerous households are exposed to high levels of the gas released from the soil. This radioactive gas is odourless, tasteless, and colourless, making it difficult to detect, and can infiltrate homes and enclosed spaces through various openings such as cracks in foundation floors and walls, construction joints, and gaps around service pipes, among others. Shockingly, it is the primary cause of lung cancer in non-smokers, silently claiming the lives of 3,300 Canadians annually, more than those killed in car accidents, house fires, and carbon monoxide incidents combined.

Due to their airtightness features, Canadian homes are particularly susceptible to trapping radon gas, leading to potentially hazardous levels that can damage the DNA in lung tissue with prolonged exposure.

According to Health Canada, about 16 per cent of lung cancer fatalities are attributed to radon exposure within homes. Despite this, the frequency of radon testing among homeowners remains low. In fact, a recent study conducted by Health Canada indicates that merely six per cent of Canadians have conducted a radon test in their residences.

To protect Canadians from radon buildup, the contractor and builder communities need to consider building code measures that will control radon entry, especially as government incentives to protect against radon accumulation increase. With increased public interest in protecting homes from radon, contractors and builders need to have plans and products in mind to tackle this issue.

This article will explore active and passive radon mitigation systems, and the surprising role that certain closed-cell spray foam insulation (ccSPF) products can play in creating a radon barrier in residential homes.

Active and passive radon measures

Regarding radon mitigation, there exist two fundamental approaches: passive barriers, which consist of a collection of pipes and a stack riser that leads to the roof without a mechanical fan, and active devices, which comprise a passive barrier system along with a mechanical fan.

However, it is essential that all radon control measures include a depressurization zone (gravel) situated below the plane of airtightness. Once these components are in place and connected to the occupied space, the next step is to implement either a passive or active method to extract the soil gas from beneath the slab and release it into the atmosphere. In the non-powered passive approach, depressurization is created through natural convection forces, such as a stack effect or positive pressure zone. The stack extends through the building shell and releases ideally above the roof or the rim joist. As warmer air from the vent stack rises, it naturally depressurizes below the slab. To preserve the momentum of the stack effect, the section of the stack that runs through the attic should be insulated, and a hardwired receptacle must also be installed to allow for future conversion to an active system.

Sometimes, a passive system cannot move enough radon out of a home, and a powered, active approach is necessary. This is not too different, as it just involves an electric fan installed in the same type of venting system which actively draws air up through the stack. In both active and passive methods, it is crucial to have a continuous air-soil gas control layer and permeable material to establish a depressurization zone.

Determining radon levels within residential homes

To accurately measure radon levels in a home, testing must be conducted after construction and under normal living conditions. Unfortunately, there are currently no reliable or affordable methods to predict if a home will have high radon levels prior to construction. Therefore, it is necessary to enforce code requirements that regulate the entry of radon in all residential buildings.

To control soil gas ingress during new construction and renovations, various measures can be taken. These include applying soil gas barriers to ground contact floors, foundation walls, and roofs, installing a gas collection layer (such as clear stone or gas mat) under all ground contact floors, setting up a piping system to extract soil gas from beneath the floors, sealing seams, cracks, penetrations, and all openings in ground contact floors, walls, and roofs, and conducting post-construction radon level testing.

If the indoor radon concentrations are found to be above Health Canada’s action level, the piping system can be connected to an extraction fan to control radon entry and safely vent the accumulated radon outdoors.

Obtaining a perfect air barrier/soil gas barrier is virtually impossible using conventional construction methods such as sheeting and taping.

HFO Closed-Cell Spray Foam Insulation (ccSPF) as a cost-effective solution

Air leakage is the primary pathway for soil gas intrusion, which occurs through joints, cracks, and penetrations in buildings. Therefore, it is crucial to ensure that these areas are well sealed and that the soil gas barrier is continuous. Spray foam insulation, when applied correctly by authorised and certified professionals, can expand into crevices, and adhere to building elements, making it an effective option for creating a continuous soil gas barrier. This method can be used under-slab, on foundation walls, and on roofs. Additionally, spray foam insulation can help to minimize construction defects that may be present in taped or caulked radon barrier systems.

Although spray foam insulation is not a new product or invention, recent developments have led to the creation of hydrofluoroolefin (HFO) based closed-cell spray foam insulation products that have been tested for radon diffusion and have proven to be highly effective in reducing radon levels.

Typically, an air barrier material is used for radon protection since radon primarily travels through the air. However, some air barrier materials may allow radon diffusion. For this reason, ccSPF products have been tested in accordance with K124/02/95 (method C of ISO/TS 11665-13) for radon diffusion. At a one inch in thickness, some HFO ccSPF products have been found to perform 35 times better than a 6-mil (0.15 mm) polyethylene sheet for radon protection.

To account for the unevenness of the gravel bed, typically 1.5 inches of ccSPF is used. Initially, less than an inch is applied in the first pass to level out the substrate. Then, a final application of one inch is applied on top of the preliminary layer. This approach utilizes ccSPF for its barrier properties, while also acting as insulation.

A slab that has been insulated with 1.5 inches of ccSPF has in average an R-10 rating, which meets most code requirements for slab insulation. In many regions, 1.5 inches of ccSPF is adequate to address the requirements for a subfloor vapor retarder. Additionally, using under slab insulation has numerous benefits such as being hydronic heating ready, preventing cold concrete floors, saving energy through the thermal mass effect, reducing floor cracking, and preventing condensation which can lead to mold growth.

Why does ccSPF work so well as a radon control layer?

• To start, it’s seamless. The ccSPF ensures a smooth and uninterrupted surface coverage. The reliability of the polyethylene barrier’s continuity is dependent on the installation’s precision and the tape’s durability. The use of caulking or mastics to supplement the barrier, as well as concerns over termination edge failures and material compatibility, can be eliminated.
• ccSPF is also water resistant. ccSPF has a slow water absorption rate and if it does become wet, it will eventually dry out and remain resistant to fungi. It also serves as a vapor retardant when it reaches a thickness of 1.25 inches and has received approval from the Federal Emergency Management Agency (FEMA) for use as insulation in flood zones.
• The requirements for an air barrier are exceeded by ccSPF. To comply with ASTM E23 or CAN/ULC S742, which is the standard test method for determining air leakage rate of air barrier assemblies, air barrier solutions need to be tested as systems. For this requirement, the tested tape must be used in conjunction with 6-mil (0.15 mm) polyethylene. In commercial construction, ccSPF is a frequently used insulating air barrier system that has undergone an air barrier system test and an additional durability test procedure, which confirmed its compliance with air barrier system test standards after being exposed to the Canadian climate for a full year.

Best practices for control and continuity layers

When aiming for continuity between the insulation on the walls, rim joist, and sub-slab, spray foam insulation can be applied directly onto the prepared gravel substrate, which should have a minimum thickness of 1.5 inches. This area is a crucial one for air leakage and thermal bypass. The application rate may vary depending on the job’s complexity, but typically, installing both the air and vapor control layer and insulation in a 1000 square feet basement (wall, rim joist, and under slab) can be done in half a day. This production rate is much faster compared to installing 6-mil (0.15 mm) polyethylene sheet, which requires seaming and detailing all penetrations, followed by insulating and seaming the insulation boards.

In terms of ccSPF’s seal and self-flashing capability, each penetration is entirely sealed, and the joint is insulated, resulting in no thermal shocking. The concrete and penetrations become part of the thermal envelope, which eliminates thermal expansion for the pipe and makes the concrete-to-pipe seal permanent. The concrete is thermally protected and no longer prone to shrinkage, which often results in cracks. Additionally, the sump pump lid is also sealed.

Radon mitigation for retrofits

Adding ccSPF as a radon control layer on the existing slab and a new second slab can complete basement retrofits for radon mitigation. To ensure effective radon mitigation, the radon vent stack must penetrate both slabs and terminate within the permeable fill layer.

Existing floor penetrations can be sealed and insulated by directly applying 1.5 inches of ccSPF to the existing concrete floor. This is also an opportune time to install hydronic heating. If the load-bearing wall needs to be isolated, it’s recommended to wrap plywood with commercial-grade air barrier material and install them before pouring the second concrete floor.

For a crawlspace, ccSPF can be applied directly onto the original floor slab or over the gravel. The spray foam will adhere fully to both surfaces. Retrofit applications can also be done over the original floor slab in a full basement, using a total of 1.5 inches of ccSPF, reinforced with rebar, with a hydronic heating system installed, and concrete applied.

Government incentives and grants for testing and mitigating radon

As the Canadian government pushes for more recognition of and testing for radon accumulation in residential homes, there are a few incentives and grants that have appeared across Canada. As awareness of the dangers of radon, and the presence of government grants to combat it grow, there will be more opportunity for contractors and builders to take on radon mitigation projects. As a contractor or builder, don’t miss out on what is likely to become a pressing issue in the years to come, and be prepared with the right products and procedures to combat radon buildup.

How to choose ccSPF products that most effectively resist radon

There are multiple spray foam insulation products on the market, so how can you know which most effectively resists radon buildup within a home? As a contractor or builder, you know that ccSPF is an effective measure for combatting radon buildup when properly installed. It’s best to look for spray foam insulation that has radon diffusion testing or has been evaluated by the Canadian Construction Materials Centre (CCMC) as suitable for radon control. The CCMC operates under the National Research Council of Canada (NRC), and objectively evaluates the performance of various materials and products on the market to ensure they comply with regulations.

Table sourced from NRC Canada Government website [CCMC 14280-R]

The table above demonstrates the good performance of the ccSPF product. There wasn’t a significant amount of radon that diffused through the ccSPF product and therefore, the radon coefficient (before and after mechanical damage) and resistance are negligible. The radon infiltration percentage on the large-scale test also demonstrates the superiority of ccSPF over a 6-mil polyethylene.

Selecting a spray foam insulation that has been rigorously examined by a team of unbiased experts is the best way to choose a product that will effectively mitigate radon buildup, while also contributing to an excellent building envelope that can be implemented into new builds and retrofits alike.