How to Mitigate Radon in a Condo, Duplex, or Multi-Unit Building

The Ownership Structure Problem

Radon mitigation in multi-unit buildings isn't just a technical challenge — it's a governance challenge. The foundation is shared property; the unit interiors are owned individually. This creates a decision-making split that doesn't exist in single-family homes.

The typical structure:

• Foundation, sub-slab, and exterior: Common elements → HOA responsibility
• Interior unit air quality: Unit owner domain
• Pipe routing through common areas: Requires HOA approval
• Fan installation on exterior or roof: HOA jurisdiction

In practice, this means: if you own a ground-floor condo and want radon mitigation, you can't just hire a contractor and start drilling through the foundation. You need HOA involvement.

Condos: Engaging the HOA

Step 1: Test your unit

Get a test result in writing. Ground-floor unit testing above 4.0 pCi/L is your evidence for an HOA request.

Step 2: Request a building-wide assessment

Frame the request to the HOA as a building-wide issue, not just your unit. The EPA action level applies to the building, not just your stack of air. A certified contractor should assess the full building.

Step 3: Make the case

• Radon is an EPA-documented health risk
• Mitigation is a fixed cost, not an ongoing expense
• Unmitigated buildings face disclosure liability at every unit sale
• One building-level system is far cheaper per unit than individual solutions

Step 4: HOA approval and contractor engagement

Once the HOA agrees to proceed, they engage the contractor, authorize foundation work, and manage pipe routing approvals through common areas.

Duplexes and Small Multi-Family Buildings

For a duplex or small multi-family building with a shared foundation:

Shared ownership (you own the whole building): Straightforward — mitigate as you would a large single-family home. One system for the full footprint.

Shared ownership with a co-owner: Both owners need to agree. The system benefits both units equally — cost sharing should be proportional.

Rental property: You own the building; radon mitigation is your responsibility. In states with radon rental regulations, elevated radon in a rental building creates disclosure and possibly remediation obligations.

Technical Approach for Multi-Unit Buildings

The sub-slab depressurization approach is the same as for single-family homes — the scale is larger:

• Multiple suction points: Larger footprints require multiple core-drilled holes to achieve pressure field coverage across the full slab
• Larger fan or multiple fans: A single fan may not be sufficient for a large building; GX5-class fans or multiple fans in series/parallel are common
• Building-wide pipe network: Suction points connect via PVC pipe runs to one or more fans; routing through utility chases, mechanical rooms, or exterior walls

An experienced contractor should perform a building-wide sub-slab communication assessment before designing the system — confirming how many suction points are needed and where.

Apartments and Renters

If you're renting in a multi-unit building, your options are limited. You can:

• Test your unit (within your rights)
• Request building mitigation in writing from your landlord
• Escalate to state housing authorities in states with tenant radon protections
• Monitor with a continuous detector while the issue is being addressed

Upper-floor apartments have meaningfully lower risk than ground-floor and basement units. If you have the option of a higher floor, it's a legitimate radon risk reduction.

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