Radon Mitigation System Inspection: What Inspectors Check and What You Receive

The Two Types of Post-Installation Verification

Homeowners are often confused because the word "inspection" is used loosely for two different things. Understanding the difference prevents scheduling mistakes and missed steps.

1. Building or Electrical Permit Inspection

If your contractor pulled an electrical permit for the radon fan circuit (required in many municipalities), you will need a final inspection by your local building department. This inspection is about code compliance — not about whether radon levels dropped. The inspector verifies that the electrical work meets code, the fan is properly mounted, and the installation conforms to what was permitted.

2. Post-Mitigation Radon Test

Regardless of whether a permit was required, every mitigation installation should be followed by a radon test to verify that levels have actually dropped. This is done with a radon test device — either by you (using a mail-in kit) or by a certified radon measurement professional. Some states require a certified tester for the post-mitigation result; others do not. This test is about effectiveness, not code compliance.

Building and Electrical Inspection: What to Expect

If an electrical permit was required in your municipality, your contractor should have scheduled the final inspection as part of the job. You should not need to do anything except be home during the inspection window (usually a 2–4 hour arrival window).

The building inspector arrives, reviews the permit, and examines the installation. The inspection typically takes 15–30 minutes. At the end, the inspector either:

• Signs off (passes): The permit is closed. You receive documentation that the work passed inspection. Keep this document — it is valuable at resale.
• Issues a correction notice: Specific items must be corrected before the permit closes. Your contractor is responsible for the corrections; a re-inspection will be scheduled.

If your contractor did not mention a permit or inspection, ask them directly: "Did you pull any permits for this job, and is there a final inspection required?" A permit that is pulled but never closed (final inspection never scheduled) can create problems when you sell the home — a title search will show an open permit.

What a Building Inspector Checks on a Radon Mitigation System

Building inspectors typically do not have specialized radon training. They are checking code compliance for the electrical work and general installation quality. A typical inspection covers:

The Post-Mitigation Radon Test: The Test That Actually Matters

The post-mitigation radon test is the most important verification step. It tells you whether the system is actually working — whether radon levels in your home have dropped to an acceptable level.

Who Conducts the Test

Requirements vary by state:

• States requiring certified tester: Pennsylvania, Illinois, Minnesota, Maryland, New Jersey, Virginia, and others require that post-mitigation tests be conducted by a state-certified radon measurement professional. Your contractor cannot self-certify their own work in these states.
• States without this requirement: Ohio, Indiana, Wisconsin, and many others allow homeowners to conduct their own post-mitigation test using a mail-in charcoal canister kit (available at hardware stores for $15–$30 or online).

Even in states that don't require it, having the post-mitigation test conducted by an independent certified professional adds credibility to your documentation — especially useful if you plan to sell the home.

Where to Place the Post-Mitigation Test Device

Place the test device in the same location (or as close as possible) where the original high-reading test was conducted. This allows a direct comparison. The lowest livable level of the home is the standard placement — finished basement if applicable, first floor if there is no finished basement.

Timing: When to Schedule Each Step

1. Immediately after installation: Ask your contractor whether they pulled a permit and whether a final inspection is required. If so, confirm they are scheduling it — it should not be your responsibility to track this, but verify.
2. 24–48 hours after installation: You may begin your post-mitigation radon test. AARST and EPA both recommend waiting at least 24 hours to allow the system to stabilize pressure conditions under the slab. In practice, 48 hours is better before deploying a test device.
3. 2–7 days after deployment: For a short-term charcoal canister test, retrieve the canister and mail it per the kit instructions. Allow 7–14 business days for lab results.
4. Building inspection window: Usually scheduled within 1–4 weeks of permit application, depending on your local building department's current workload. Your contractor should coordinate this date.
5. When results arrive: Compare to your pre-mitigation level. Target is below 4 pCi/L, ideally below 2 pCi/L. If results are still above 4 pCi/L, contact your contractor — the system may need adjustment (additional suction point, fan upgrade, or slab penetration sealing).

Documentation You Should Receive and Keep

After a complete mitigation installation and inspection process, you should have the following documentation. Keep these in a home maintenance file — they are valuable at resale and for insurance purposes.

• Contractor's written invoice or work order with: installation date, system description, fan model and serial number, contractor name and NRPP/NRSB certification number
• Pre-mitigation radon test result (the one that prompted the work)
• Post-mitigation radon test result (independent laboratory report)
• Closed permit documentation from your local building department (if a permit was required)
• System warranty — most radon fans carry a 5-year manufacturer's warranty; some contractors offer a workmanship warranty
• Contractor's instructions for system monitoring (how to check the manometer, when to schedule re-testing)

What Happens If the Post-Mitigation Test Shows Levels Still Above 4 pCi/L?

Approximately 10–15% of initial radon mitigation installations do not achieve the target level on the first attempt. This is not a disaster — it is a known issue that certified contractors are trained to address.

Common reasons a system underperforms:

• Inadequate sub-slab communication. Dense or debris-filled fill material under the slab limits how far the suction point depressurizes. Solution: add a second suction point in a different location.
• Air pathway to above-slab space. If the slab or foundation walls have significant cracks or openings, outdoor or indoor air mixes with the sub-slab air, reducing the pressure differential. Solution: additional slab sealing.
• Undersized fan. Some homes require a higher-CFM or higher-pressure fan than originally installed. Solution: fan upgrade.
• Crawl space not addressed. If the home has both a basement and a crawl space and only one zone was mitigated. Solution: add crawl space encapsulation or a separate suction point for that zone.

A reputable contractor will diagnose and correct system underperformance at no or reduced charge, especially if they offer a post-mitigation guarantee. Ask about this guarantee before signing any contract — many certified contractors guarantee achieving below 4 pCi/L or will return to adjust at no additional cost.

Frequently Asked Questions