Radon gas, produced by the radioactive decay of uranium in Alberta’s soils and bedrock, has emerged as one of the most significant indoor air quality concerns for new residential construction in the province. Geological surveys have established much of Alberta, including Calgary and surrounding regions, as radon-prone zones, necessitating a robust, code-compliant-and ideally, high-performance-approach to sub-slab gas barriers. The importance of specifying both appropriate material thickness and installation quality for polyethylene radon barriers cannot be overstated; insufficient barrier durability or integrity can contribute to elevated radon ingress, triggering health risks and long-term liabilities for owners and builders.

Minimum Polyethylene Thickness: Code Prescription Versus Functional Performance

Alberta Building Code Requirements: The 6-Mil Baseline

The National Building Code - 2023 Alberta Edition mandates that conditioned floor spaces on ground incorporate an air barrier to reduce the potential for soil gas infiltration. This is functionally achieved by the installation of a polyethylene sheet beneath the floor slab, specified at a minimum thickness of 0.15 mm (6 mils), and in compliance with CAN/CGSB-51.34-M. This Canadian General Standards Board standard assures a basic level of physical performance: tensile strength, impact resistance, and minimal vapor transmission. Adopting this standard ensures uniformity across residential builds in Alberta and provides a regulatory reference point for builder accountability, inspection, and warranty policies.

However, it is well-established among construction professionals that minimum compliance standards do not always translate to optimal in-service performance. NBC 9.13.4.2. states the 6-mil thickness as a baseline, not an ideal or “best practice.” Experiences from job sites consistently show delicate vapor barriers at or near 6-mil dimension are vulnerable: a single inadvertent drag of rebar, an errant boot step, or sharp aggregate beneath the sheet is likely to cause puncture or tearing. Even with conscientious placement, subsequent trade work and slab prep processes continue to threaten integrity. Small openings-whether visible or sub-perceptible-compound rapidly across large footprints, undermining the radon-resistance objective embedded in code itself.

Material Standards: Understanding CAN/CGSB-51.34-M

CAN/CGSB-51.34-M prescribes not only minimum thickness but also specific material performance parameters. These include tensile strength across and along the roll direction, elongation at break, resistance to low-temperature cracking, and water vapor transmission rate. The testing protocol is intended to guarantee that a 6-mil barrier will maintain some level of gas impermeability even after basic installation stresses. However, the standard was originally conceived for general vapor barriers-primarily for condensation and moisture exclusion-not specifically for aggressive soil gas mitigation. Radon, being a noble gas with high mobility, demands more rigorous solutions than the lowest permissible thickness.

In the context of Alberta’s climate and site realities (variable soil moisture, freeze-thaw cycles, differential settlement, and rigorous construction traffic), the selection of merely code-minimum polyethylene runs counter to the long-term interests of asset managers and residents. Market feedback and insurance claims increasingly reflect the hidden costs of using minimally compliant barriers-particularly in multifamily projects where floor area, trade density and schedule intensification multiply potential points of failure.

Health Canada and CAN/CGSB-149.11-2024: Raising the Standard

Health Canada’s perspective on radon risk, shaped by epidemiological research and extensive radon mapping, recognizes that even moderate indoor concentrations present a significant carcinogenic risk over time. As a result, Health Canada guidelines, while not legislatively binding in all provinces, provide design authorities, consultants, and builders with actionable best practices grounded in prudent risk management.

Health Canada currently recommends installation of a polyethylene or equivalent polyolefin membrane with a minimum thickness of 10 mils (0.25 mm) for radon protection, with overlapped and taped seams, and verified puncture and gas resistance. The latest CAN/CGSB-149.11-2024 standard codifies this approach, effectively doubling the baseline requirement for slab gas barriers. The document stresses that puncture resistance and cumulative mechanical durability must be anticipated well beyond the immediate pour timeframe, as post-pour slab settlement, micro-cracking, and differential loading can challenge the gas barrier envelope for the lifetime of the building.

From a risk transfer perspective, aligning new construction with the Health Canada/CGSB-149.11-2024 10-mil baseline not only reduces future remediation liabilities but complies with a growing number of municipal procurement specifications (e.g., Calgary’s own affordable housing requirements and certain provincial grant eligibility criteria). Across Canada, forward-looking warranty providers are beginning to condition their radon coverage on documented use of higher-performance barriers, further tilting the balance toward thicker membranes.

The Technical Perspective: Puncture Resistance and Gas Permeance

Puncture resistance for polyethylene barriers increases exponentially with thickness. Heavier membranes (10 mils and above) combine better tensile strength and greater flexibility, distributing stresses and reducing the likelihood of microcracks under point loading. Tears at corners, around service penetrations, or across re-entrant slab geometry are drastically reduced. In-situ testing and lab analysis confirm that while a 6-mil sheet is adequate for vapor diffusion, its effectiveness as a soil gas-and especially radon-barrier is compromised by typical construction-site abrasions. Additionally, the improved gas permeability ratings for thicker or top-coated sheets make a significant difference in radon-affected zones, particularly where sub-slab depressurization systems are either deferred or omitted.

Industry Best Practices: Practical Implications for Trades and Construction Sequencing

Thicker Polyethylene: Real-World Performance in Alberta Slab Construction

• Reduced Patching and Repair: Site observations over hundreds of Alberta multifamily projects confirm that thicker (10-15 mil) polyethylene sheets are less prone to accidental punctures, especially under high-traffic areas such as service chases, formwork drop-off points, and material stockpiles. The number of repairs and field patches required drops substantially, reducing both labor cost and schedule risk.
• Improved Adhesion and Sealing at Penetrations: Utilities passing through the slab-plumbing stacks, sumps, radon node pipes-require meticulous air and gas sealing. Thicker membranes offer a more forgiving edge for cut-outs, achieve more robust tape adhesion, and retain stretch without tearing during post-pour movement. This reduces the risk of creating inadvertent “chimney effects” for radon transport at pipe penetrations.
• Enhanced Quality Control: Inspections are simplified when membranes maintain shape under foot traffic rather than bunching or curling, and any accidental breaches are more visible for prompt addressing prior to the pour. Supervisors and third-party radon verifiers cite fewer non-conformance reports on jobs where 10-mil or heavier sheets are standard.
• Compatibility with Other Slab Systems: Heavy duty gas barriers are less likely to be displaced or compromised during the mesh/rebar placer’s work, mechanical curve fitting, or slab insulation install. Where under-slab hydronic radiant heating lines are specified, the risk of thermal expansion/contraction causing membrane stress concentrations is also reduced with thicker sheet stock.

Moreover, specifying a 10-mil (or thicker) membrane at the design/tender phase facilitates proper pricing and trade alignment. Contractors can stage slab construction with greater assurance of barrier integrity, while downstream trades-responsible for mechanical, electrical, or IT conduit-face less operational disruption and warranty risk.

The Tradeoff: Cost, Durability, and Lifecycle Value

Cost Premiums: Material Versus Total Installed Cost

For a typical new multifamily development, the raw material cost difference between a 6-mil and a 10-mil (or 15-mil) polyethylene barrier is not linear, but it is relatively modest at scale, especially when purchased as part of a bundled project order. According to recent supplier quotes in Alberta, 10-mil branded barriers can be 1.8-2.3 times the cost per square meter of 6-mil alternatives. However, project managers and independent estimating consultants note a more meaningful distinction when factoring in labor and schedule impacts: thicker sheets, owing to their resilience, reduce on-site “re-inspection and repair” rounds and permit tighter control of trade sequencing. This produces back-end savings by lowering inspection hold-ups and minimizing late-stage slab warranty claims.

The additional upfront material outlay thus yields a positive return on investment when considered against likely (and often underbudgeted) remediation work for radon migration-ranging from limited site-specific “interventions” (caulking, grouting, or sub-slab depressurization retrofits) to more disruptive and expensive slab repairs or system overhauls.

Risk Management: Warranty Implications and Remediation Scenarios

Beyond the direct construction logic, the industry trend toward thicker radon barriers is closely aligned with improved long-term risk transfer and warranty defensibility. In the event of radon exceedances measured post-occupancy-a scenario that is not uncommon, especially as public awareness and testing rates increase-builders are exposed to not only remediation costs but also reputational harm. Demonstrating that a project did more than code minimums, by installing a robust 10-mil or thicker membrane with certified penetrations and taped seams, materially strengthens the builder’s position under new home warranty programs and with insurance adjusters.

Remediation of sub-slab radon infiltration in occupied multifamily buildings is especially disruptive and expensive. Retrofitting active sub-slab depressurization systems, sealing new barrier material from above, or jackhammering access points all carry substantial lifecycle penalties compared to the up-front discipline of specifying a thoroughly robust underslab gas barrier.

Vendor Innovation: Beyond Basic Polyethylene-Composite Barriers and Gas-Selective Membranes

Manufacturers have responded to the increasing industry demand for radon-focused barriers with several advanced product lines. Composite barriers, such as those incorporating ethylene vinyl alcohol (EVOH) cores or cross-laminated polyethylene, achieve dramatically lower gas permeance while further improving tear and puncture resistance.

• PERMINATOR EVOH: Available in up to 20-mil thickness, this underslab gas vapor barrier is designed specifically to restrict radon as well as methane and other soil gases. Its multilayer construction offers strong resistance to both mechanical and chemical degradation, and its permeability to radon is an order of magnitude lower than standard 10-mil polyethylene. For high-density multifamily or mixed-use slabs, this material offers a technically superior-albeit costlier-option, especially where soil gas concentrations are confirmed via site geotechnical analysis to be elevated.
• VaporLock and Stego Wrap: Competing composite membranes also boast performance attributes tailored to large residential or light commercial slab assemblies where radon, vapor, and potential hydrocarbon exclusion are prioritized. These products often include third-party verification of radon permeance per ASTM or ISO protocols, which provides specification writers and consulting engineers with robust risk-mitigation documentation for owner groups.

While the price point of these specialty products may limit their application to premium projects or especially challenging sites, their technical merits underscore a key trend: the market is moving steadily beyond the notion of a “one size fits all” polyethylene solution. Site-specific due diligence, including preconstruction radon risk mapping, will increasingly drive the call for targeted, certified, and installation-ready materials over and above the bare minimum.

Sub-Slab Barrier Installation: Achieving Practical Integrity in Alberta’s Climate

Typical Failure Modes: Construction Damage and Imperfect Detailing

Even where 6-mil barriers are used and installed to manufacturer instructions, real-world conditions in Alberta construction present frequent risks to barrier integrity. Under the pressure of tight schedules, trade congestion, and evolving site logistics, the following issues predominate:

• Punctures from Sharp Aggregate: Despite worksite cleaning, sharp gravel or reuse of fill can pose a common puncture risk, especially during late-stage slab prep or when mesh is dropped prior to the pour.
• Foot Traffic and Equipment: Telehandler wheels, wheelbarrow runs, and concentrated foot traffic over the same routes (especially in poor weather) deform and abrade membranes, often leaving micro-tears.
• Penetrations and Post-Install Work: Late electrical, plumbing or HVAC layout changes may require precise cutting and resealing, with attendant risks of holes beyond the immediate repair zone if the material is thin.
• Membrane “Creep” and Displacement: In colder weather, lower-grade polyethylenes can stiffen, with the result that slabs settle on wrinkles or curled areas, breaking the intended contiguous air and gas seal.

The aggregate effect of undetected breaches may not manifest until well after occupancy, detectable only through indoor air radon testing. Remediation at that point is arduous, with effectiveness uncertain. Conversely, the use of thicker, more robust membranes directly mitigates most of these site hazards, creating a practical buffer against both accidental and cumulative construction damage.

Detailing Seams, Joints, and Penetrations: From Code Standard to Best-in-Class

Both the Alberta Building Code and Health Canada recognize that gas barrier performance is heavily dependent on the treatment of seams and slab penetrations. Proper overlap (minimum 150 mm or 6 inches), aggressive taping with compatible butyl or acrylic tapes, and consistent compression under the slab are critical details. With thicker barriers, these installation steps are not only more reliable but remain more durable over time.

Edge detailing-where the membrane terminates at grade beam, pier, or foundation wall-demands positive sealing, mechanical anchoring, and secondary overlap. In particular, where the slab interfaces with cold joints or kicker plates, transition tapes or bonded mastic can be integrated into the detail assembly, further securing the air barrier continuity. Some sites supplement with optional “bathtub” returns, anchoring the barrier to wall waterproofing or below-slab radon sumps for further risk reduction.

Project documentation should record barrier pre-pour inspections, detailing photographs, and as-built plans showing membrane coverage, joint treatments, and penetration sleeves. This documentation increasingly forms part of warranty handover packages and can be a key defense if radon migration is detected in service.

Owner, Developer, and Investor Perspectives: Resale, Risk, and Reputation

For long-hold owners and institutional investors in Alberta’s multifamily sector, radon mitigation is more than a statutory or health-driven consideration; it increasingly factors into asset longevity, marketability, and even ESG reporting. Properties with demonstrable, above-code radon protection can command a premium at sale or refinancing, both by mitigating the risk of future “sick building” liabilities and by aligning with evolving disclosure expectations and lender requirements.

Additionally, municipalities and housing authorities that operate or fund large inventories are actively recalibrating their procurement standards around Health Canada and CAN/CGSB-149.11-2024 recommendations. Tendering criteria may now require not only the use of 10-mil or better barriers but post-installation radon monitoring, occupant education, and even third-party QA of the slab envelope. Developers who proactively integrate thicker membranes and certified installation are not only “future proofing” their builds from regulatory tightening, but burnishing their credentials among institutional purchasers and tenants alike.

Case Studies: Deployment of 10-mil and High-Performance Barriers Across Alberta

Recent multifamily developments in Calgary, Red Deer, and Edmonton illustrate the real-world application and benefits of thicker gas barriers. In one 120-unit wood-frame infill project near the Bow River, consultants specified a 10-mil, cross-laminated polyethylene product, noting significantly reduced field repairs and zero reported post-occupancy radon events. Mechanical coordination meetings flagged under-slab sleeves and penetrations months prior to slab pour, enabling advanced fabrication of custom-edged wraps and seals, resulting in minimal schedule impacts even when late changes occurred.

Large-format multi-tower podium projects present higher risk exposure, both by virtue of their slab area and the intensity of follow-on trades. A 378-unit project in Edmonton’s university district chose a 15-mil composite radon barrier, motivated in part by site geotechnical data indicating above-average radon generation from localized glacial till. Core-cutting and post-tensioned cable systems required selective “booting” and double-taping around anchors and conduits. Post-construction air quality monitoring recorded radon levels below 30 Bq/m³ in every suite-substantially lower than Health Canada’s 200 Bq/m³ guideline-while competing projects nearby, using 6-mil, showed several units needing supplementary remediation.

In Alberta’s rural multifamily market, affordable housing developments demonstrate another benefit: with lower per-door budgets, the additional cost of a 10-mil upgrade is more than covered by reduced post-occupancy troubleshooting and durable WCB and warranty alignment. Owners of such properties now report better tenant satisfaction and improved funding eligibility for deep energy retrofit programs recognizing exceeding code requirements.

Design and Specification: Practical Guidance for Alberta’s High-Performance Projects

• Specifying the Right Thickness: For most Alberta conditions, adopting a 10-mil minimum polyethylene or equivalent composite barrier provides the optimum balance of regulatory compliance, construction resilience, and lifecycle performance. Heavier (15-mil plus) membranes should be evaluated for projects anticipating significant slab complexity, trade intensity, or high radon risk (based on geotechnical reports).
• Detailing Protocols: Specifications should explicitly require continuous, overlapped (minimum 150 mm), and fully taped seams-using chemical-resistant tape compatible with the chosen barrier. Pipe and conduit penetrations must be sleeved, with boots or collars tailored to membrane gauge and backflashed with radon-rated tapes or mastics.
• Quality Assurance: Submittals must include cut sheet data for membrane thickness, gas permeance ratings, and puncture resistance (per ASTM or ISO methods). Field inspection hold points should address full site coverage, damage repair, and edge detailing-documented with geo-tagged photos and field reports for handover inclusion.
• Coordination and Training: Early-stage pre-construction meetings, bringing together concrete, mechanical, and envelope trades, ensure sequencing and responsibilities are clear and that membrane repairs are performed by trained personnel. Mock-ups of penetrations and edge returns are recommended for complex jobs.

It is important that these practices not be viewed as “added scope,” but rather as investments in the resilience of the building, the health of its residents, and the reputation of the ownership and construction team alike.

The Future: Regulatory Trends and Radon-Ready Certification in Alberta

Provincial and municipal regulators have signposted increased attention to radon as a building health hazard, particularly as awareness grows among homeowners and public health professionals. There is clear evidence that upward pressure on code minimums is probable in the next ABC revision cycle, with several Canadian provinces piloting requirements consistent with Health Canada’s 10-mil membrane recommendation or calling out CAN/CGSB-149.11-2024 directly.

Concomitantly, Canada Mortgage and Housing Corporation (CMHC) and other funding agencies have released “radon ready” documentation packages and scoring rubrics for new housing, rewarding above-baseline specification, certified testing, and documented mitigation protocols. Alberta’s multifamily developers, by standardizing on 10-mil plus membranes and maintaining robust as-built records, position themselves to benefit from these programs and shift future cost curves downward.

Implications for Existing Stock and Renovations

While the focus here is on new construction, the rapidly shifting consensus on radon control is already shaping the retrofit and major renovation market. Projects involving partial slab removal, new service rough-ins, or “change of use” upgrades (such as converting ground-floor parkades to suite space) are increasingly being scoped for radon barrier installations at the new, more robust thicknesses. Detailed project closeout documentation of sub-slab work is becoming a de facto standard, not only for regulatory compliance but for prudent asset management.

Summary: Requirements and Recommendations for Alberta Multifamily Projects

• Code Minimum (Alberta Building Code): 6-mil (0.15 mm) polyethylene sheet, CAN/CGSB-51.34-M compliant, with overlapped and sealed seams.
• Health Canada & CAN/CGSB-149.11-2024 Recommendation: 10-mil (0.25 mm) polyethylene or equivalent polyolefin, gas and puncture resistant, with taped, air-tight seams and penetrations.
• Industry Best Practice: 10-15 mil composite or multi-layer specialty barriers, particularly in high-risk areas or large-format multifamily construction, with thorough QA documentation and installation by trained trades.
• Installation Imperatives: Meticulous overlap, compatible tape selection, sensitive detailing at all penetrations, boots and edge seals, and pre-pour damage checks form the foundation of effective radon mitigation under Alberta slabs.

The common denominator across advanced developments is clear: while code sets a minimum standard, practical experience and leading-edge research overwhelmingly support a shift toward thicker, high-durability polyethylene membranes for reliable, long-term radon mitigation in Alberta’s multifamily sector. Durability, permeability, and ease of installation all benefit-yielding a safer, healthier built environment and a futureproofed investment.

At Kingsway Builders, commitment to technical excellence and thorough attention to under-slab radon mitigation ensure lasting value and peace of mind for every multifamily project undertaken in Alberta.