Crawl Space Radon Mitigation Toronto: Sub-Membrane Depressurization

# Crawl Space Radon Mitigation Toronto: Sub-Membrane Depressurization

Toronto sits on Paleozoic limestone with moderate radon potential. Health Canada recommends mitigation when long-term radon levels exceed 200 Bq/m3. A conditioned (encapsulated) crawl space is the ideal substrate for sub-membrane depressurization — a 4-inch perforated pipe under the vapor barrier connected to a dedicated fan that exhausts radon-bearing soil gas above the roof line.

This post covers the mitigation design, fan sizing, the sequencing decision (install the suction tee during encapsulation even if current radon is low), and the contractor coordination model. For the full project context, see the pillar [Crawl Space Encapsulation Toronto Complete Guide](/blog/crawl-space-encapsulation-toronto-2026-complete-guide). For the broader Toronto radon picture, see the radon pillar [Radon Mitigation Toronto Complete Guide](/blog/radon-mitigation-toronto-2026-complete-guide).

Toronto Radon: What the Numbers Show

Health Canada's 2017 Cross-Canada Survey and subsequent C-NRPP data:

• Toronto and the GTA: roughly 5% to 8% of homes above 200 Bq/m3.
• Hot zones: parts of Etobicoke, Scarborough, and the postwar suburbs north of the 401.
• Older central Toronto neighbourhoods (East York, Beaches, Junction, Cabbagetown): typically lower averages but very high variance, with individual homes well above threshold.

Crawl spaces concentrate radon because the soil gas has direct contact with indoor air through the dirt floor. Encapsulation alone reduces radon entry, but if the underlying soil flux is high, active depressurization is required to reach Health Canada's target.

When to Test

A C-NRPP-certified long-term radon test (3 to 12 months) is the gold standard. We recommend:

• Pre-encapsulation if homeowner has any radon concern.
• Post-encapsulation 90 days after sealing.
• Long-term monitoring with a continuous radon monitor (Airthings View Plus, Corentium Pro) for ongoing visibility.

The Sub-Membrane Suction Tee: Always Install It

The single most important decision in a Toronto crawl encapsulation: install the radon suction tee under the membrane even if current radon levels are low. The tee is a passive layer until a fan is added.

Why install the tee always:

• Cost during encapsulation: $300 to $500.
• Cost to retrofit later (cut and reseal membrane): $1,500 to $3,000.
• Risk: post-encapsulation testing sometimes shows higher radon (because the air exchange is reduced), requiring mitigation that is now more expensive.

The tee design:

• 1. 4-inch perforated PVC pipe laid in a trench under the future membrane location, gravel bed.
• 2. Pipe terminates in a vertical riser through the membrane (sealed boot).
• 3. Riser runs up to the rim joist or out through the foundation wall, terminating in a capped tee.
• 4. If radon levels are above 200 Bq/m3 post-encapsulation, the cap is removed and a fan is installed in-line.

Fan Sizing and Installation

The two fans we use most often:

• RadonAway RP145. 145 CFM, mid-range static pressure. Toronto workhorse for typical 1,000 to 2,000 sq ft crawls.
• Festa AMG Pro Series. Variable models from 90 to 300 CFM. Quiet operation, premium build.

Installation:

• Fan mounted outside the conditioned envelope — typically in the attic or on an exterior wall — so a fan failure cannot push radon into the home.
• Discharge stack runs above the roof line, terminating 12 inches above the roof and 10 ft from any window or air intake (per Canadian C-NRPP guidance).
• 24/7 operation.
• 110V circuit; consumption is 30 to 70 watts.
• Manometer (U-tube water gauge) at the riser to verify suction.

Cost: $1,200 to $2,500 for fan, stack, electrical, and commissioning. Plus $400 to $1,000 for post-mitigation testing.

Honest Positioning

RenoHouse self-performs the suction-tee rough-in during encapsulation. For the fan installation, full mitigation system, and post-mitigation testing, we partner with a C-NRPP-certified radon mitigation specialist. Toronto firms include Radon Environmental, Radonova Canada, and several local C-NRPP independents.

Why we draw this line: Health Canada and C-NRPP require certification for the design, installation, and verification of mitigation systems. The suction-tee rough-in (a passive pipe under the membrane) is renovation work, which is ours. The fan, stack, manometer, and post-mitigation testing are mitigation specialty.

Sequencing With Other Crawl Work

The Toronto sequence we recommend:

• 1. Pre-encapsulation radon test if homeowner is concerned.
• 2. Asbestos and vermiculite abatement if applicable (Pinchin, EHS).
• 3. Pest trap-out and exclusion if applicable (Orkin, Terminix).
• 4. Mold remediation and PRV if applicable.
• 5. Encapsulation with radon suction-tee rough-in installed.
• 6. Post-encapsulation radon test (90-day minimum).
• 7. If above 200 Bq/m3, C-NRPP-certified specialist installs fan.

Real Toronto Examples

• Etobicoke postwar bungalow: pre-encapsulation 380 Bq/m3, post-encapsulation 290, with fan 75. Three-week timeline including fan install.
• East York 1920s detached: pre-encapsulation 180, post-encapsulation 110. No fan needed; passive tee monitored annually.
• Junction 1930s detached: pre-encapsulation 90, post-encapsulation 140. Within Health Canada threshold; passive tee in place. Homeowner installed Airthings monitor for ongoing visibility.

Get a Radon-Ready Encapsulation

Free crawl inspection with radon discussion and rough-in spec at [/services/home-renovation/crawl-space-encapsulation](/services/home-renovation/crawl-space-encapsulation). If your home tests above 200 Bq/m3 we coordinate the fan install with a C-NRPP-certified specialist as a pass-through on the project.