What is the difference between sub-slab depressurization and sub-membrane depressurization for radon in a GTA home?

Sub-slab depressurization creates suction beneath the concrete basement floor, while sub-membrane depressurization uses suction beneath a plastic membrane installed over exposed soil or gravel. Both systems prevent radon gas from entering your home, but the choice depends on your basement's construction and soil conditions.

Sub-slab depressurization is the most common radon mitigation system in finished GTA basements. A hole is cored through the concrete basement floor (typically 4-6 inches in diameter) and a PVC pipe is inserted into the aggregate layer beneath the slab. A radon fan installed in the attic or outside the home creates continuous suction, drawing radon gas from beneath the foundation before it can enter the basement. The system vents the gas safely above the roofline. This works well in homes with poured concrete floors over a gravel base — which describes most GTA homes built after 1960.

Sub-membrane depressurization is used when there's no concrete slab or when the existing slab has too many penetrations to seal effectively. A plastic membrane (typically 6-mil polyethylene) is installed over exposed soil, gravel, or a damaged concrete floor, then sealed around the perimeter and all penetrations. Suction pipes beneath the membrane draw radon gas away before it can migrate through the plastic. This approach is common in crawl spaces, dirt-floor basements, or older GTA homes with deteriorated concrete floors that would be expensive to repair.

GTA-specific considerations make system selection important. Many pre-war Toronto homes in neighbourhoods like Cabbagetown, Riverdale, and the Annex have stone foundations with dirt or gravel floors that are ideal candidates for sub-membrane systems. Post-war bungalows across Scarborough, North York, and Etobicoke typically have concrete slabs suitable for sub-slab systems. However, Toronto's clay soil conditions can complicate both approaches — clay's low permeability may require multiple suction points or higher-capacity fans to achieve adequate depressurization.

Installation costs in the GTA range from $1,500-$3,500 for sub-slab systems and $2,000-$4,500 for sub-membrane systems. Sub-membrane installations are typically more expensive because they require more extensive sealing work and often larger membrane areas. Both systems require electrical work by an ESA-licensed contractor to power the fan, and some municipalities require building permits for radon mitigation systems.

Effectiveness is similar for both systems when properly installed — both can reduce radon levels by 80-99%. The key is achieving adequate soil depressurization (typically 0.2-1.0 inches of water column) beneath the foundation. Post-installation testing is essential to verify the system is working, and annual radon testing ensures continued effectiveness.

When to Hire a Pro — radon mitigation requires specialized knowledge of soil conditions, fan sizing, and proper venting to prevent backdrafting of combustion appliances. Improper installation can actually increase radon levels or create carbon monoxide hazards. Always use a certified radon mitigation contractor and verify the system with post-installation testing by an independent radon measurement professional.

Need help finding a radon mitigation specialist? Toronto Basement Remodeling can match you with qualified professionals through the Toronto Construction Network.