As many as 3,300 Canadians die from it every year. It easily penetrates buildings and enclosed spaces undetected. It’s the number one cause of lung cancer in non-smokers. It’s radon – a radioactive gas released by the breakdown of uranium in the soil. Throughout Canada, there are buildings with elevated levels of radon that need to be assessed and treated.

Canadian buildings are typically constructed and “sealed” to protect against extreme weather, but this also makes them a prime target for radon. When it becomes “captive” in a building, radon can reach dangerously high levels, and with long-term exposure, causes harm to the DNA in our lung tissue.

According to a recent study commissioned by The Government of Canada, only 6% of buildings have been tested for radon. As part of their commitment to reducing the number of radon-induced cancer deaths in Canada, the Canadian government, along with various partners, stakeholders, and community leaders, encourage Canadians to test their buildings for radon, reduce high levels of the gas and protect their health.

Role of architects and builders in education and building-owner protection

 Radon management focuses on two key municipal actions. But to make any impact, they require the participation of the architect and builder community. They are:

• Overseeing the building process – by considering building code measures that will control radon entry, and
• Incentivizing building owners – to work with architects to install mitigation systems and get assistance in radon protection and/or removal through mitigation grants.

When it comes to radon mitigation, there are active and passive measures to consider. For architects and builders, the consideration lies with two basic types of radon mitigation implementation options. “Passive barriers” is one that is defined as the collection of pipes and stack riser through the roof with no mechanical fan. Then there’s the active barrier system option with the addition of a mechanical fan, we call this “active devices”.

Essential throughout this process is ensuring that all radon control measures contain a depressurization zone(gravel) below the plane of airtightness. Following installation, which should include a connection to the occupied space, this is where either a passive or active method is required to “move” the soil gas from below the slab to the atmosphere.

In the nonpowered passive approach, depressurization happens through natural convective forces, such as a stack effect or positive pressure zone. The stack extends up through the building shell and vents above the roof. When the air in the vent stack is warmer than outdoors, the air naturally rises, depressurizing below the slab. To preserve the stack effect momentum, the section of the stack running through the attic should be well insulated, and a hardwired receptacle should also be installed to facilitate conversion to an active system.

Conducive to the powered active approach, an electric fan is placed in the vent, actively pulling air up through the stack and developing depressurization. Both active and passive methods must contain a continuous air-soil gas control layer and permeable material to create a depressurization zone.

How to determine radon levels in buildings

There is currently no reliable or affordable method to determine if a building will have high radon levels before its construction. The only way to assess radon levels in a building is to test it after construction, under normal occupied conditions. For this reason, there are code requirements to control the ingress of radon for all residences.

You can manage soil gas ingress in new construction and renovations using methods such as:

1. Apply soil gas barriers to ground contact floors, foundation walls and roofs,
2. Create a gas collection layer (e.g., clear stone or gas mat) under all ground contact floors,
3. Install a piping system for the extraction of soil gas from under the floors,
4. Seal seams, cracks and all openings in ground contact floors, walls, and roofs; and
5. Test the radon levels in the building after construction. If the indoor radon concentrations exceed the Health Canada action level, the piping system can be connected to an extraction fan to control radon entry and exhaust the accumulated radon safely outdoors.

With mandates in place, you would think that all building codes require indoor radon testing after construction, but some do not. It’s important that the construction industry understand that it’s pretty much impossible to create a perfect air barrier/soil gas barrier using conventional construction methods like sheeting and taping.

A cost-effective and protective solution – HFO Closed-Cell Spray Foam Insulation

Radon gets in through the soil, and soil gas intrusion happens mostly through air leakage. That said, not just any sealant will do. A soil gas barrier with seamless continuity must be able to reach all the joints, cracks, and penetrations. This is where Huntsman Building Solutions’ HFO closed-cell spray foam insulation (ccSPF) performs. Thanks to its ability to expand into the smallest crevasses and adhere to nearly all substrates, properly applied ccSPF can provide a continuous soil gas barrier – from under-slab, to foundation walls and roofs. In taped or caulked radon barrier system assemblies, it can even reduce construction deficiencies.

Tested for radon-resistance and provides an effective air/vapour/gas barrier

Huntsman Building Solutions’ hydrofluoroolefin (HFO) based closed-cell ccSPF insulation products have been tested for radon diffusion and are highly radon-resistant. When installed properly, they can protect a building from the ground up.

Radon travels primarily through the air, so you need an effective air barrier material. The key word here is “effective,” because there can still be radon diffusion through some air barrier materials. Therefore, some ccSPF products have been tested in accordance with K124/02/95 (method C of ISO/TS 11665-13) for radon diffusion. At only 1’’, some HFO ccSPF performs 35 times better than a 6-mil (0.15 mm) polyethylene sheet for radon protection. These ccSPF products are also often installed at a thickness of 1-1⁄2” to 2’’ which makes them much harder to puncture than 6-mil polyethylene (for example, when workers are walking on it during construction).

Our ccSPF Canadian products are even “specialist approved,” having been evaluated to outperform a polyethylene sheet by a National Radon Proficiency Program (CNRPP) (Radon Specialist) officer in Canada.

(HFO) based closed-cell insulation is high performing and versatile

HFO closed-cell insulation has several other distinct advantages besides serving as a high-performing substitute for the air/gas and vapor control layers. Typically, in a radon-mitigation application, 1.5” of ccSPF is applied to correct the “unevenness” of the gravel bed – using less than an inch in the first pass to level out the substrate, then a final application of 1” applied on top of the preliminary layer.

Going beyond its excellent barrier properties, ccSPF also acts as insulation. For example, a slab with 1.5” of ccSPF (as described above) has around an R-10 rating, which meets most code requirements for slab insulation. For most products, 1.5” of ccSPF also meets the requirements for a subfloor vapor retarder. Under slab insulation has its own list of benefits as well: it makes floors hydronic heating ready, eliminates cold concrete floors, saves energy through thermal mass effect, helps to prevent floor cracking, eliminates condensation and prevents mold growth. It also helps with by providing:

1. A continuous barrier: polyethylene barriers rely on the durability of the tape and the precision of its installation to be seamless. Since ccSPF adheres to any substrate, it eliminates the need for additional materials like caulking or mastics and helps to avoid termination edge failures and material compatibility issues.
2. Resistance to water and fungi: ccSPF takes a very long time to absorb water and if it does, once the source of water is removed, it dries out while being resistant to fungi. It also becomes, depending on the product brand, a vapor retardant starting at 1.25’’ and is approved by the Federal Emergency Management Agency (FEMA) for use as insulation in flood zones.
3. Protection from punctures: you can walk on ccSPF without puncturing it, which saves both time and money. That’s because when you lay polyethylene on gravel and then walk on it, which you must do to pour concrete, it gets punctured. ccSPF eliminates the need for repairing holes before the pour.
4. Compliance in air barrier standards: Air barrier solutions should be tested as systems to ASTM E2357, “Standard Test Method for Determining Air Leakage Rate of Air Barrier Assemblies” or CAN/ULC S742. The 6-mil (0.15 mm) polyethylene must be used with the tested tape to meet this requirement. ccSPF is commonly used as an insulating air barrier system in commercial construction. It has been tested as an air barrier system and gone through an additional durability test procedure to confirm its air barrier system test compliance after a full year of exposure to the Canadian climate; and finally
5. Cost efficiencies: ccSPF can be installed quickly, reducing labour hours. It also has a lower production cost per square foot. This is because the applicator’s travel time and prep are offset by the volume to install, compared to conventional insulation systems with multiple steps and materials, plus more labour, which also leaves more room for error.

Process overview for (HFO) ccSPF measures in radon control layers

Most primary air leakage and thermal bypass happens in the area between the insulation on the walls, rim joist and sub-slab. This is where spray foam insulation can be sprayed directly onto the prepared gravel substrate (minimum 1.5”) to achieve continuity in this area.

In most scenarios, you can install both the air and vapour control layer and insulation in a 1,000 square feet basement (wall, rim joist and under slab), in just half a day. Compare that to the time it would take to insulating and seaming the insulation boards, then install a 6-mil (0.15 mm) polyethylene sheet, seaming and detailing all the penetrations. Efficient indeed.

You will appreciate ccSPF’s sealing and self-flashing capability, because upon application each penetration is completely sealed, and the joint is insulated, with no thermal shocking. Since the concrete and penetrations become part of the thermal envelope, the pipe is no longer subject to thermal expansion and the concrete-to-pipe seal is permanent. The concrete also becomes thermally protected, no longer subject to shrinkage resulting in cracks. Even the sump pump lid is sealed.

After the concrete has fully cured, you can install the interior finishing walls and apply gypsum drywall. The foam cannot be left exposed and must be protected with an approved thermal barrier (drywall will act as such).

A hydronic heating system can also be installed and installers can walk on the surface for not only the rebar but also the heating system. Concrete is then laid over top of the ccSPF surface. Once the concrete is in place, there’s no need for additional vapour control layers, or tape for the structural framing members – the installation is impervious.

Huntsman Building Solutions’ HFO ccSPF is ideal for radon mitigation retrofits

Retrofitting a building for radon mitigation by adding ccSPF as a radon control layer, can be done on the existing slab and before a new second slab is poured. Ensure that the radon vent stack penetrates both slabs and terminates within the permeable fill layer.

Any existing floor penetrations can be sealed and insulated with 1.5” of ccSPF applied directly to the existing concrete floor. Hydronic heating can also be easily installed at this point. If the designer or contractor wants to isolate the load-bearing wall, it is best practice to wrap the plywood with a commercial-grade air barrier material and install them before pouring the second concrete floor.

For crawlspaces, ccSPF can be applied directly to the ground, the gravel or the original floor slab. The spray foam will fully adhere to all surfaces. You can also do retrofit applications over the original floor slab in a full basement. You’ll need to use a total of 1.5” ccSPF, reinforced with rebar overtop and, as an option, a hydronic heating system installed, and finish by applying concrete.

The continuity and durability of ccSPF as an effective barrier against radon, depend both on the product you choose and installer’s skills. The product should only ever be installed by professionals trained by Huntsman Building Solutions and its third party. In Canada, training is provided by ISO-certified trainers, and then the installation is inspected by ISO-certified inspectors. That said, always do your research and check credentials when choosing your HFO ccSPF.

Maxime Duzyk is the director of building science and engineering with Huntsman Building Solutions. He holds a background in architecture and has been in the spray foam insulation business for the last 10 years. Maxime is involved with different building envelope committees and associations in North America like CSC, SFC, SPFA, CCMC and ULC Standards.