Protecting Buildings from Radon with Closed-Cell Spray Foam Insulation

Written by Maxime Duzyk, Huntsman Building Solutions

It’s odourless, tasteless, colourless, and it’s silently killing 3,300 Canadians per year.  It easily enters 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.  There are buildings with elevated levels of radon everywhere in Canada right now. 

We Need to Test More Buildings for Radon 

Because Canadian buildings are typically ‘sealed’ to protect against our extreme weather, it 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 Health Canada, only six per cent 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, have declared November ‘Radon Action Month’ – encouraging Canadians to test their buildings for radon, reduce high levels of the gas and protect their health.

Contractors and Builders: 

This is Your Chance to Help Educate and Protect Building Owners Against Radon

This year’s Radon Action Month focuses on two key municipal actions.  But in order to make any impact, they require the participation of the contractor and builder community.  They are:

  • Protecting buildings while they are being built – by considering building code measures that will control radon entry, and 
  • Providing incentives to building owners – to work with contractors to install mitigation systems and get assistance in radon protection and/or removal through mitigation grants.
A PVC Radon vent pipe which leads from a sub-slab mitigation system to an attic fan and out the roof

Radon Mitigation – Active and Passive Measures to Take

As a contractor or builder, there are two basic types of radon mitigation approaches you can implement: 

  1. Passive barriers,’ defined as the collection of pipes and stack riser through the roof with no mechanical fan; and 
  2. Active devices,’ defined as a passive barrier system with the addition of a mechanical fan.

One important thing to note though: all radon control measures must contain a depressurization zone (gravel) below the plane of air tightness.  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.

For the non-powered 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. 

For 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.

Determining Radon Levels in Buildings – How to Do It

Believe it or not, there is currently no reliable or affordable method to determine if a building will or won’t have high radon levels before its construction.  The only way to determine radon levels in a building is to test it after construction under normal occupied conditions.  This is why 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 the following methods:

  • Apply soil gas barriers to ground contact floors, foundation walls and roofs, 
  • Provide a gas collection layer (e.g., clear stone or gas mat) under all ground contact floors, 
  • Install a piping system for the extraction of soil gas from under the floors, 
  • Seal seams, cracks and all openings in ground contact floors, walls and roofs; and 
  • 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. 

You would think that all building codes would mandate 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.

To quote from a study prepared for the 14th Canadian Conference On Building Science and Technology: “There is an entrenched belief that simply extending the continuity of the air barrier through the building foundation, as prescribed by the national and some provincial building codes, is sufficient on its own to control indoor radon levels.  These views are contrary to the findings of Health Canada and extensive evidence and experience from relevant agencies in the United States and Europe.”

Closed-cell spray foam spraying for protection from Radon in large buildings. Courtesy of Huntsman Building Solutions

HFO Closed-Cell Spray Foam Insulation (ccSPF):

Why it’s a Cost-Effective, Protective Powerhouse 

Knowing that radon gets in through the soil, and soil gas intrusion happens mostly through air leakage, not just any sealant will do.  A soil gas barrier with good continuity must be able to reach all the joints, cracks and penetrations. Enter (literally) HFO closed cell spray foam insulation (ccSPF).  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. 

ccSPF Has Been Tested Extensively for Radon-Resistance and is an Effective Air/Vapour/Gas Barrier

There are some hydrofluoroolefin (HFO) -based closed-cell spray foam (ccSPF) insulation products that have been tested for radon diffusion and are highly radon-resistant. Installed properly, they can help protect a building from the ground up.

Since radon travels primarily through the air, 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.  This is why some ccSPF products have been tested in accordance with K124/02/95 (method C of ISO/TS 11665-13) for radon diffusion.  At only one-inch, some HFO ccSPF performs 35 times better than a six-mil (0.15 mm) polyethylene sheet for radon protection.  These ccSPF products are also often installed at a thickness of 1.5-inches to 2’-inches, which makes them much harder to puncture than 6-mil polyethylene (for example, when workers are walking on it during construction). 

Some HFO based ccSPF Canadian products are even ‘specialist approved,’ having been evaluated to outperform a polyethylene sheet by a National Radon Proficiency Program (C-NRPP) (Radon Specialist) officer in Canada.

Courtesy of Huntsman Building Solutions

Why ccSPF is the Ultimate Efficiency Multitasker 

Besides serving as a high-performing substitute for the air/gas and vapour control layers, ccSPF has a number of other distinct advantages as well.  Typically, in a radon-mitigation application, 1.5-inches 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 one-inch applied on top of the preliminary layer. 

Adding to its excellent barrier properties, ccSPF also acts as insulation.  For example, a slab with 1.5-inches of ccSPF (as described above) has around an R-10 rating, which meets most code requirements for slab insulation.  For most products, 1.5-inches of ccSPF also meets the requirements for a subfloor vapour 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 mould growth. 

Other benefits of ccSPF as a radon control layer include:

  • Seamless coverage: polyethylene barriers rely on the durability of the tape and the precision of its installation to be a continuous barrier.  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. 
  • It’s water-resistant: 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 vapour retardant starting at 1.25-inches and is approved by the Federal Emergency Management Agency (FEMA) for use as insulation in flood zones.
  • It’s puncture-resistant: 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. 
  • It exceeds requirements for air barriers: Air barrier solutions should be tested as systems to ASTM E2357, ‘Standard Test Method for Determining Air Leakage Rate of Air Barrier Assemblies.’  The six-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. 
  • It’s cost-effective: 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.
Courtesy of Huntsman Building Solutions

Using ccSPF for Radon Control Layers – Process Overview 

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

In most cases, you can install both the air and vapour control layer and insulation in a 1,000-square-foot 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 six-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. 

A good example of using a hydronic-heating system requires installers to walk on the surface, for not only the rebar but also the heating system.  If the insulation and radon control layer remain in place with no punctures, concrete is then laid directly on top of the ccSPF surface.  After concrete, there’s no need for additional vapour control layers, or tape for the structural framing members – the installation is completely sealed. 

Courtesy of Huntsman Building Solutions

Using ccSPF for Radon Mitigation Retrofits – Process Overview 

You can retrofit a building for radon mitigation by adding ccSPF as a radon control layer on the existing slab and a new second slab.  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-inches 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 original floor slab, directly onto gravel and carried over onto the existing concrete slab floor.  The spray foam will fully adhere to both 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-inches ccSPF, reinforced with rebar overtop with a hydronic-heating system installed, and finish by applying concrete. 

But ccSPF Only Works When it’s Installed Properly by Trained professionals

Yes, ccSPF is proven to be an effective barrier against radon, but its continuity and durability depend both on the product you choose and installer’s skills.  Improper application can have some serious and expensive consequences.  ccSPF should only ever be installed by professionals trained by the manufacturer and its third party for their specific system.  In Canada, training is provided by ISO-certified trainers, and then the installation is inspected by ISO-certified inspectors.  Bottom line: do your research and check credentials when choosing your closed cell spray foam insulation. 

Maxime Duzyk

About the Author:

Maxime Duzyk is the director of building science and engineering, North America with Huntsman Building Solutions.  Duzyk has been in the spray foam insulation business for the last 10 years.