Radon Mitigation Basics Reference

Why this reference exists

Radon is the leading cause of lung cancer in non-smokers + the second-leading cause overall. The EPA estimates 21,000 U.S. deaths/year. About 1 in 15 U.S. homes has radon above the 4 pCi/L action level. Mitigation systems sell for + require specialized but learnable installation. Many HVAC + basement-finishing crews add radon mitigation as an adjacent service line. This reference is the working summary.

What radon is + where it comes from

Radon is a naturally-occurring radioactive gas from uranium decay in soil + rock. Colorless, odorless, tasteless. Released into the air everywhere; outdoor concentrations are low (~0.4 pCi/L average). Indoor air can accumulate radon when:

• Building sits on uranium-bearing geology (granite, shale, phosphate)
• Soil + rock around foundation is permeable
• House has lower air pressure than surrounding soil (most do, especially in winter)
• Foundation cracks + penetrations let radon in

Radon levels are not predictable by region only - adjacent homes can vary 10x. Testing is the only way to know.

EPA action level

• Below 2 pCi/L: low; no action needed
• 2-4 pCi/L: consider mitigation
• 4+ pCi/L: EPA recommends mitigation
• 10+ pCi/L: urgent mitigation; minimize occupancy in basement until fixed
• 20+ pCi/L: emergency; some authorities recommend immediate occupancy reduction

Real estate transactions in many states trigger mandatory disclosure + testing. Real estate testing is short-term (48 hours, charcoal canister). Long-term testing (3-12 months, alpha track detector) gives a more accurate seasonal average.

How mitigation works

The dominant residential mitigation: Active Soil Depressurization (ASD). A fan pulls air from below the slab + exhausts above the roof line. The slab + foundation become a sealed surface that air no longer migrates THROUGH.

Components:

• Suction point(s) under slab - typically PVC pipe penetrating slab
• Sealed sump pit (if present)
• Vertical riser pipe through interior or exterior of house
• Inline fan (Radonaway RP145, RP265; Festa Eagle, similar)
• Exit point above roofline OR away from windows + intakes
• Manometer (U-tube water column) showing suction; visible to customer
• Sealed cracks + penetrations in slab

Mitigation typically reduces radon 80-99%.

Site assessment

Step 1: Test for baseline radon

Long-term test (alpha track 3-12 months) OR short-term (charcoal 48 hours). Customer-paid; mitigator provides referrals or testing.

Step 2: Inspect foundation

• Slab on grade (basement floor)
• Crawl space (open dirt floor or partial slab)
• Sump pit (often the suction point)
• Cracks + penetrations (utility pipes, water lines, expansion joints)

Step 3: Plan suction points

• 1 point per 2,000 sq ft of slab typical
• More if slab is interrupted by foundation walls, partitions, additions
• Sub-slab communication test: drill small hole, run vacuum, measure pressure at distant point - if pressure pulls, communication is good

Step 4: Plan riser route

• Interior route: through unfinished basement up through utility chase or closet
• Exterior route: PVC pipe up exterior wall (faster install, visible)
• Exit above roofline; 10+ ft from windows + intakes; 2+ ft above eave

Step 5: Plan electrical

• 120V dedicated circuit for fan
• Switch in conditioned space for service shutoff
• Manometer accessible

Standard install procedure

Step 1: Cut slab + create suction pit

1. 6" diameter core-drill or saw-cut slab
2. Excavate 18-24" of gravel + dirt below to create suction pit
3. Verify suction communication (test with vacuum + manometer)

Step 2: Install suction pipe

1. 3" or 4" PVC pipe through slab to suction pit
2. Seal slab around pipe with polyurethane sealant
3. Reduce to 3" for riser run (most fans 3")

Step 3: Run riser pipe

1. PVC SDR-21 or SCH-40 pipe + fittings
2. Route to exterior or up through interior
3. Insulate runs in unconditioned space (prevents winter condensation)

Step 4: Install fan

1. Mount in unconditioned space (attic OR exterior wall outside livable space)
2. Boot connections
3. 120V wire to switch + breaker
4. Manometer installed visible in basement

Step 5: Exit pipe

1. Run pipe above roofline (typically through gable end + up, or vertical through roof flashing)
2. 10+ ft from windows + intakes
3. 2+ ft above eave
4. Bird screen at exit

Step 6: Seal + commission

1. Seal slab cracks + penetrations with polyurethane sealant
2. Seal sump pit (if present) with a sealed cover allowing pump access
3. Energize fan
4. Verify manometer reading (typically 0.5-1.5 in WC of water column = good)
5. Customer briefing

Step 7: Re-test after install

Run a post-mitigation radon test (3-7 days, short-term). Provide results to customer. EPA + state programs typically require this.

Acceptance criteria

• Post-mitigation radon < 2 pCi/L (best) or below action level
• Manometer reading within design range
• All slab cracks + penetrations sealed
• Fan operating + audible
• Customer signed work order
• Post-mitigation test results delivered

Common pitfalls

• Wrong fan size: too small = no suction, too big = wasted energy + noise
• Bad exit location: 5 ft from window = radon re-entry
• Unsealed slab cracks: fan pulls air from cracks (short-circuit) rather than soil
• Sump uncovered: huge air leak path
• No manometer: customer can't see whether fan is running
• Pipe through conditioned space without insulation: condensation drips
• Fan inside living space: noise complaint + maintenance access
• No post-mitigation test: customer + agency wants verification

Crawl space variant

Open dirt-floor crawl spaces use a different approach:

• Lay 6-mil polyethylene over dirt
• Seal seams + edges to foundation walls
• Penetrate with suction pipe under the sheeting
• Same fan + riser system as ASD

Encapsulating a crawl space is often combined with radon mitigation since the membrane is needed for both. Higher ticket: combined.

Radon-resistant new construction (RRNC)

For new builds, designing radon resistance during construction:

• Gravel layer below slab (passive collection medium)
• Capped passive vent pipe from gravel up through roof
• Sealed all slab penetrations
• Polyethylene under slab
• Easy fan-activation if later test shows high

Costs in new construction; saves if mitigation later needed.

State + utility incentives

Some states + utilities subsidize radon mitigation:

• Maine, Minnesota, Pennsylvania, Iowa have state programs
• Utility energy efficiency programs sometimes include if ERV/HRV bundled
• Health-department programs for low-income households

Verify locally; typical rebate when offered.

Certifications

References

• EPA Citizen's Guide to Radon
• EPA Radon Mitigation Standards (ANSI-AARST)
• NRPP + NRSB Certification + Training
• State radon program contacts
• Manuall internal: Indoor Air Quality - ERV and HRV Reference