Sub-Slab Depressurization — Kentucky's #1 Radon Mitigation Method

Sub-Slab Depressurization (SSD), also called Active Sub-Slab Depressurization (ASD), is the most common radon mitigation method in Kentucky and across the United States. The system uses a continuous-duty fan to draw soil gas out from beneath a building's foundation slab, through a sealed PVC stack, and out above the roofline. One (or sometimes multiple) suction points are cored through the basement slab into the gravel or weathered-limestone fill underneath. ASD accounts for roughly 80% of Kentucky residential mitigation installs, particularly in the basement-heavy housing stock of Louisville, Lexington, and Frankfort.

ASD works on a pressure-gradient principle. A continuous-duty radon fan creates lower air pressure beneath the foundation slab than above it. Because gas flows from higher pressure to lower pressure, soil gas (including radon) is drawn outward through the suction point rather than upward into the home through cracks and slab penetrations. The system requires: (1) a 3–6 inch suction point cored through the slab into the granular or weathered-limestone layer beneath, (2) sealed schedule 40 PVC piping from the suction point through the home to the roof, (3) a continuous-duty radon fan (typically RadonAway GP301 — 79 watts, 195 CFM in Kentucky residential installs), (4) polyurethane sealing of slab cracks and penetrations to maintain the negative-pressure field, and (5) an exhaust outlet above the roofline meeting EPA placement requirements.

Four reasons ASD dominates Kentucky installs: (1) Effectiveness — properly designed ASD systems reduce indoor radon by 70–99%, the highest reduction of any single mitigation method. (2) Cost-efficiency — typical Kentucky install $800–$2,200, with Louisville Metro median around $1,000–$1,500 per ProMatcher data. (3) Foundation compatibility — ASD is the perfect match for the poured-concrete basements that dominate Louisville, Lexington, Frankfort, Owensboro, and Inner Bluegrass housing stock. (4) AARST-ANSI standardization — the method is well-documented in industry standards and is the core curriculum of NRPP/NRSB certification, which combined with KBRS contractor registration produces consistent, defensible results.

Five mitigation methods, with ASD as the Kentucky default for poured-concrete basements: (1) Active Sub-Slab Depressurization (ASD) — basement-slab homes, $800–$2,200, ~80% of installs. (2) Sub-Membrane Depressurization — crawl-space homes (common in Bowling Green / karst belt), $1,500–$3,500. (3) Block-Wall Depressurization — older Eastern Kentucky homes with hollow concrete block foundation walls, $2,000–$4,000. (4) Drain-Tile Depressurization — homes with continuous perimeter drain tile, $1,500–$3,500. (5) Passive System Activation — converting builder-installed passive stacks (some Northern Kentucky new construction), $500–$1,500. Foundation type and geology determine which method applies; ASD covers the clear majority of Kentucky cases.

Six core components: (1) Suction point — 3–6 inch diameter core hole through the slab into the gravel or weathered-limestone layer beneath, fitted with a PVC riser and sealed with polyurethane caulk. (2) PVC piping — schedule 40, typically 3 or 4 inch diameter, routed from suction point through the home to the roof. (3) Radon fan — continuous-duty centrifugal fan (RadonAway GP301, Festa AMG, or Fantech HP-190 are the common Kentucky choices). (4) Manometer — u-tube fluid gauge mounted inline showing the system is pulling. (5) Sealing materials — polyurethane sealant for slab penetrations and visible cracks. (6) Dedicated electrical circuit (typically 110V) for the fan. Materials total $300–$600; labor accounts for the balance of the install price.

Four manufacturers dominate Kentucky ASD installs: (1) RadonAway GP301 — 79 watts, 195 CFM at 0 in. w.c. The default for most Louisville, Lexington, and Frankfort residential applications. 5-year manufacturer warranty. Component cost $250–$350. (2) Festa AMG-Series — 195–365 CFM, energy-efficient. Used on larger Inner Bluegrass basements or commercial properties in Owensboro and Covington. (3) Fantech HP-190 / HP-220 — inline configuration with lower noise profile, common in finished-attic installations and Northern Kentucky suburbs. (4) AMG Series 750 — commercial grade up to 750 CFM for HUD multi-family, schools, and large commercial buildings. The right fan is determined by basement size, soil-gas permeability under the slab, and the post-mitigation target pCi/L.

AARST-ANSI (American Association of Radon Scientists and Technologists — American National Standards Institute) standards for residential radon mitigation include: (1) Suction point placement informed by diagnostic measurements, not arbitrary location. (2) All PVC piping joints sealed with primer and cement, not slip-fit. (3) Exhaust outlet at least 10 feet above grade and at least 10 feet from any operable window, door, or air intake. (4) Continuous-duty fan rated for radon service. (5) Manometer installed inline for system monitoring. (6) Visible slab cracks sealed during install. (7) Post-mitigation verification testing within 30 days. (8) Written documentation of design and install provided to homeowner. KBRS-registered, NRPP-certified Kentucky mitigators are trained to AARST-ANSI standards.

A typical Kentucky residential ASD install takes 4–8 hours of on-site work, split across three phases: (1) Site assessment and suction-point creation (1–2 hours) — diagnostic measurement, coring the suction point through the slab. (2) Piping routing and fan installation (2–4 hours) — running PVC from suction point through the home to the roof, mounting the fan, electrical connection. (3) Sealing, manometer installation, and system activation (1–2 hours). Post-install, allow 48–96 hours for verification testing before considering the project complete. Crawl-space sub-membrane jobs in the karst belt typically run 1–2 days because of additional vapor-barrier work.

Not as a paid contractor. Kentucky transferred radon oversight to the Kentucky Board of Radon Safety on July 1, 2024, and KRS §§ 309.430–309.454 require KBRS contractor registration on top of NRPP or NRSB certification for anyone offering paid radon mitigation services. A homeowner working on their own property is not explicitly banned from physical work, but an uncertified install has no legal standing for the seller-disclosure form required under KRS § 324.360, will not satisfy FHA/VA/USDA appraiser conditions, and cannot be documented as a "mitigated" home in any future real estate transaction. For any home that may be sold, refinanced, or insured, professional installation is the only defensible path.

A quality Kentucky ASD install typically includes: (1) Lifetime warranty on PVC piping and structural components (they do not wear). (2) 5-year manufacturer warranty on the radon fan (standard for RadonAway GP301). (3) 1-year workmanship warranty on the install labor. (4) Performance guarantee — the system must reduce indoor radon below 4 pCi/L on the first post-mitigation verification test, or the contractor will adjust at no charge. (5) Some Kentucky contractors offer 2-year service warranties that include free verification testing during the warranty period. Kentucky Radon Experts partner contractors include all five as standard, with NRPP and KBRS numbers printed on the install report.