Sub-slab depressurization (SSD) is the gold-standard method for reducing indoor radon, and it's well within reach for a confident DIYer. A professionally installed system costs $1,500–$3,000. A DIY installation using quality components typically costs $400–$700 in materials and a day of your time.
This guide walks through the complete process from start to finish — diagnosing your basement, choosing components, drilling the suction pit, routing the pipe, and verifying the system works.
How Sub-Slab Depressurization Works
The principle is straightforward: a continuously running fan creates negative pressure beneath your concrete slab, drawing radon-laden soil gas out before it can enter your living space. The gas is vented harmlessly to the exterior — typically above the roofline. As long as the fan runs, the pressure differential is maintained and radon entry is blocked.
What You'll Need
Tools:
- Rotary hammer drill with 4" core bit (or rent from a hardware store)
- PVC pipe cutter or hacksaw
- PVC primer and cement (we recommend TrimTight Cellular PVC Cement)
- Level, tape measure, pencil
- Caulking gun and polyurethane caulk
- Electrical drill and bits
- Fish tape or wire puller (if running wire through walls)
Parts and materials (shop our full selection):
- Radon fan — sized to your soil and slab conditions (see our selection guide). Most residential installs use the RadonAway RP145 or RP140.
- 4" Schedule 40 PVC pipe — available at any hardware store; quantity depends on routing distance
- PVC fittings — 90° elbows, couplings as needed
- Pipe seal or bushing — Uniseal U-Stop Bushing for penetrating a rim joist or wall
- Trim plate — 4" Trim Plate for a clean interior finish at the slab penetration
- Manometer — RadonAway U-Tube Manometer to verify the system is creating suction
- Muffler foam — noise-reducing muffler foam for fan connections
- Electrical supplies — outlet or hard-wire connection near the fan location; 8' power cord with bushing for plug-in fans
Step 1: Test the Sub-Slab Communication
Before drilling, confirm that your sub-slab material allows air to move. This is called a communication test. Drill a small (1/2" or 5/8") test hole in an inconspicuous area of the slab. Insert a vacuum cleaner hose or a shop-vac and run it for 30–60 seconds, then open to the hole and feel for suction with your hand at another floor crack or drain.
Good sub-slab communication (gravel, coarse fill) will produce clear suction across the slab. Poor communication (tight soil, dense fill directly under the slab) may require multiple suction points or a more powerful fan (see the GX4 or GX5A for tight-soil applications).
Step 2: Choose Your Suction Point Location
The suction pit location determines how effective and visually clean your system will be. Ideal locations:
- In a mechanical room, utility room, or under a staircase — keeps the pipe run hidden
- Near an exterior wall to minimize interior pipe routing
- Away from footing drains and sump pits (these need to be sealed, not used as suction points without a proper sump dome)
- Accessible for future inspection
If your basement has a sump pit, you can use it as the suction point with a Jackle Sump Dome — a sealed airtight cover that turns the sump into the depressurization entry point.
Step 3: Core the Slab
Using a rotary hammer with a 4" diamond core bit, drill through the concrete slab at your chosen location. Most residential slabs are 4" thick. Work slowly, keep the core bit wet to manage dust, and wear a P100 respirator — concrete dust is hazardous.
After coring, excavate a small suction pit beneath the slab: use a long-handled chisel or a rented jackhammer attachment to remove 1–2 gallons of sub-slab material, creating a void that allows suction to spread under the slab. A 6"–12" diameter pit improves sub-slab communication significantly.
Step 4: Route the PVC Pipe
Run 4" Schedule 40 PVC from the suction hole, up through the wall cavity or along the interior, and out through the rim joist, band joist, or roof. Use 45° or 90° elbows to navigate corners — avoid sharp bends that create back-pressure. All joints are solvent-welded with PVC primer and cement.
Key routing rules:
- The pipe must exit above the roofline if run inside a wall cavity — never terminate in a garage, attic, or adjacent to a window
- If running through conditioned space, insulate any exterior sections to prevent condensation
- Slope the pipe slightly back toward the suction pit so condensation drains down, not toward the fan
- Label the pipe "Radon Mitigation System" at all visible sections
Step 5: Mount and Connect the Fan
The fan should be installed outside the conditioned space — typically in the attic, crawlspace, outside on the exterior, or in the garage. This ensures that if the fan housing ever develops a minor leak, radon does not enter living areas.
Connect the fan inline with the PVC pipe using the fan manufacturer's connector and muffler foam to reduce vibration noise. Plug into a dedicated outlet or have an electrician hard-wire it. The fan runs 24/7 at low wattage — most models use 20–90 watts, about the same as a standard light bulb.
Step 6: Seal Foundation Entry Points
SSD works by creating negative pressure beneath the slab. Any unsealed opening in the foundation allows interior air to bypass the system. Seal all visible cracks, pipe penetrations, and openings in the slab and foundation walls with polyurethane caulk or hydraulic cement. Pay particular attention to:
- The floor-wall joint (cove joint)
- All visible cracks in the slab
- Pipe, wire, and conduit penetrations through the slab
- The sump pit lid (if not using it as the suction point, seal it airtight)
- Floor drains (a trap primer or standpipe will maintain the water seal)
Step 7: Verify the System
Install a U-tube manometer in the suction pipe — drill a small hole in the pipe and insert the manometer tap. With the fan running, the manometer should show a pressure differential (the fluid levels should be unequal). A reading of at least 1–5 Pa (0.1–0.5 inches of water column) at the pipe confirms the fan is drawing suction.
The manometer also serves as a permanent system monitor — if the fluid levels ever equalize while the fan is supposed to be running, it indicates the fan has failed or the system has a problem.
Step 8: Post-Installation Radon Test
Wait 24 hours after installation for conditions to stabilize, then place a new long-term alpha track detector in the same location as your original test. Test for a minimum of 30 days (90 days is preferred). A successful installation will typically reduce levels to below 100 Bq/m³ — often below 50 Bq/m³.
Our Long Term Alpha Track Test Kit is the standard confirmation test used by C-NRPP certified professionals.
When to Call a Professional
DIY mitigation is appropriate for most straightforward residential installs. Consider hiring a C-NRPP certified mitigator if:
- Your sub-slab communication test shows poor soil permeability
- Your home has a complex foundation (multiple slabs at different levels, crawlspace, block walls)
- Your radon level is above 600 Bq/m³ and multiple suction points may be needed
- You're not comfortable with the electrical or roofing penetration aspects
Browse our complete selection of radon mitigation fans and installation parts. Questions about which fan is right for your home? Read our fan selection guide.
