Radon Mitigation System Design & Pressure Field Extension Testing

Designing an effective radon mitigation system begins with understanding how radon moves through your home. Our certified technicians create a system tailored to your foundation type, soil conditions, and airflow patterns to ensure optimal radon reduction.

A key part of this process is Pressure Field Extension (PFE) testing. PFE testing measures how far a depressurization system affects the soil beneath your home. By temporarily activating the proposed suction points and measuring pressure changes, we can:

• Determine the optimal number and placement of suction points.

• Ensure the radon fan selected is correctly sized for your system.

• Verify that the system will effectively capture radon across the entire sub-slab area, preventing radon from entering the living spaces.

This science-based approach ensures that your radon mitigation system is efficient, reliable, and built for long-term performance, rather than relying on guesswork or generic designs.

Sub-Slab Depressurization (SSD) Systems

Sub-slab depressurization (SSD) is the most widely used and effective method for reducing radon levels in homes with concrete slab or basement foundations. This system works by creating a controlled vacuum beneath the concrete slab, drawing radon-laden soil gas away from the living space and venting it safely above the roofline.

Key features of SSD systems include:

• Suction Points: Small holes are drilled through the slab to access the soil beneath, where a network of piping collects radon gas.

• Radon Fan: A specialized, continuously operating fan maintains a negative pressure under the slab, preventing radon from entering the home.

• Piping & Venting: PVC piping carries radon safely to the exterior, typically above the roofline, ensuring it does not re-enter the home.

• Sealing & Airflow Management: Cracks, joints, and penetrations in the slab and foundation are sealed to enhance system efficiency and maintain the negative pressure field.

• Performance Verification: Pressure testing and post-install radon measurements confirm the system is effectively reducing indoor radon levels.

By actively controlling the airflow beneath the slab, SSD systems provide a long-term, reliable solution for radon mitigation, protecting both the health of your household and the integrity of your home.

Sub-Membrane Depressurization (SMD) Systems

Sub-membrane depressurization (SMD) is an effective radon mitigation method for homes with crawl spaces or dirt floors. This system works by installing a vapor-permeable membrane over the exposed soil and creating a negative pressure beneath it to capture radon gas before it can enter the living space.

Key features of SMD systems include:

• Vapor-Permeable Membrane: A durable plastic sheet is laid over the crawl space floor, sealed around the edges and any penetrations to prevent soil gas from escaping.

• Suction Points: Pipes are installed beneath the membrane to draw radon-laden soil gas into the system.

• Radon Fan: A continuously operating fan maintains a negative pressure under the membrane, safely venting radon above the roofline.

• Sealing & Airflow Management: Gaps around plumbing, vents, and crawl space walls are sealed to enhance system efficiency and maintain consistent sub-membrane depressurization.

• Performance Verification: Post-installation testing ensures the system effectively lowers radon levels and maintains a uniform pressure field under the membrane.

Sub-membrane depressurization systems provide a long-term, reliable solution for radon mitigation in crawl spaces, protecting indoor air quality while ensuring the system is energy-efficient and low-maintenance.

Active sub-slab depressurization (SSD) combined with sub-membrane depressurization (SMD)

For homes with both a basement and a crawl space, we install dual-suction systems with gate-valve dampers for post-installation balancing and optimal control.

Key Components:

• 16-mil reinforced crawl space vapor barrier, sealed to walls and piers

• Sub-membrane collection piping

• Dedicated sub-slab suction point

• Exterior-mounted radon fan

• Schedule 40 PVC riser piping

• Inline gate valve for airflow control

Why the Gate Valve Matters:
The gate valve allows technicians to:

• Balance airflow between slab and crawl space zones

• Optimize pressure field extension after installation

• Fine-tune system performance based on post-mitigation radon testing

• Reduce over- or under-depressurization in either zone

Verification:
System performance is confirmed through post-mitigation radon testing and pressure diagnostics to ensure effective radon reduction throughout the structure.

Homes with both a crawl space and slab-on-grade foundation require a radon mitigation system designed to control soil gases from multiple entry points. Best practice is a combined active depressurization system that pulls radon from beneath the slab while simultaneously collecting soil gases from the crawl space.

A sealed, reinforced crawl space vapor barrier prevents soil gas intrusion, while a dedicated sub-slab suction point depressurizes the soil beneath the slab. Both zones are connected to a single radon fan, with a gate valve installed on one branch of the system. This valve allows post-installation airflow balancing, ensuring proper pressure is maintained where it is most effective.

This approach provides greater control, improved performance, and long-term system stability—especially in homes with varying soil conditions or complex foundations.

At Smart Space, we design and install radon mitigation systems using best-practice engineering principles, not one-size-fits-all approaches. Every system is customized for performance, durability, and long-term reliability.

Schedule 40 PVC Piping

We use Schedule 40 PVC for all radon mitigation piping. This thicker, rigid pipe:

• Maintains airtight seals under continuous negative pressure

• Reduces vibration and noise

• Resists cracking, sagging, and UV degradation

• Creates a cleaner, more professional appearance

Pressure Field Extension (PFE) Testing

Before finalizing system design, we evaluate how effectively suction will extend beneath the slab or crawl space:

• Identifies whether a single suction point is sufficient

• Prevents underperforming systems that “look right” but don’t work

• Allows us to design the system correctly the first time

Proper Fan Selection Based on Site Conditions

Fan sizing is based on measured resistance and soil conditions, not guesswork:

• Avoids undersized fans that fail to reduce radon adequately

• Avoids oversized fans that create excess noise and energy use

• Ensures long-term performance and system stability

Thoughtful System Design & Routing

We design systems to balance radon reduction and aesthetics:

• Strategic exterior pipe routing to minimize visual impact

• Clean, symmetrical installations that follow the home’s architecture

• Discreet fan placement whenever possible

Exterior-Mounted Fans for Safety & Longevity

Whenever feasible, fans are mounted outside the conditioned space:

• Prevents any risk of radon re-entry if a fan ever fails

• Reduces interior noise and vibration

• Extends fan lifespan by improving airflow and cooling

Sealing & Soil-Gas Control

Radon reduction is not just about the fan:

• Sealing accessible foundation cracks and penetrations

• Installing reinforced vapor barriers in crawl spaces

• Creating a continuous soil-gas control strategy

Code-Compliant Exhaust Termination

All systems terminate:

• Above the roofline and away from windows, doors, and openings

• In compliance with national radon mitigation standards

• To ensure radon is safely dispersed away from the structure

Performance Verification & Post-Mitigation Testing

We don’t guess—we verify:

• Post-mitigation radon testing to confirm results

• Clear documentation of system performance

• Systems designed for long-term reduction, not temporary fixes