Radon Piping Layout: Suction Point to Roof Discharge
A radon mitigation system is mostly pipe. A fan does the work, but the path that pipe takes from under the slab to the open air decides how well the system performs, how quiet it is, how it looks and how long it lasts. Homeowners on the Colorado Front Range often see a white PVC pipe running up a garage wall or along the side of a house and wonder why it was routed that way. This guide explains a typical radon piping layout piece by piece: where the suction point goes, what size and type of pipe is used, why the pipe slopes, where the fan sits, where the exhaust ends, and how the manometer fits in. It summarizes EPA and CDC guidance current as of 2026; layouts vary with the house, and a certified radon mitigation professional should design and install any system. Talk to a physician about health concerns.
Part of our Radon Levels guide — start there for the full picture →
What a Radon Piping Layout Does
Most residential radon systems in basement and slab homes use an approach called active soil depressurization, sometimes called sub-slab depressurization. The EPA describes soil suction as preventing radon from entering the home by drawing the radon from below the house and venting it through a pipe, or pipes, to the air above the house, where it is quickly diluted.
The piping layout is the physical route that makes that happen. Every layout, no matter how the pipe is routed, includes the same basic parts:
- A suction point where the pipe enters the soil or gravel below the slab, sump or crawl space membrane.
- A run of solid pipe that carries soil gas from the suction point toward the outdoors.
- A fan that creates the suction, placed outside the living space.
- A discharge point where the gas is released to the open air, typically above the roof.
- A monitor, usually a U-tube manometer, that shows whether the fan is pulling suction.
Those parts work as a chain. A weak link anywhere, such as a poorly placed suction point, an undersized pipe or a leaking joint, reduces what the fan can achieve. For a broader explanation of the physics behind the system, see our guide on how a radon mitigation system works.
Radon is worth this effort. The CDC calls it an odorless, invisible radioactive gas released from rock, soil and water that can build up in homes, and notes it is the second leading cause of lung cancer deaths in the United States after cigarette smoke. For background on interpreting test results, see our Colorado radon testing overview, and for a visual walk-through of parts, our radon mitigation system diagram guide labels each component.
Layout Elements at a Glance
The table below summarizes each element of a typical layout, what installers commonly do, and the reasoning behind it. Practices vary by contractor, house and local requirements, so treat it as a general picture rather than a specification.
| Layout element | Typical practice (varies) | Why it matters |
|---|---|---|
| Suction point | Core hole through the slab with a small pit excavated beneath, often near the center of the slab or a convenient wall | The pit gives soil gas a low-resistance place to collect so suction can spread under the slab |
| Number of suction points | One for many homes; more for large slabs, split foundations or poor sub-slab airflow | Suction must reach the whole footprint to lower radon throughout |
| Pipe material and size | Solid PVC, commonly 3- or 4-inch Schedule 40 (EPA describes this for radon-resistant new construction) | Large enough diameter keeps airflow resistance and noise down |
| Labeling | Pipe marked “Radon System” at visible points | Keeps future owners and trades from cutting or tying into it |
| Slope | Horizontal runs pitched back toward the suction point | Condensation drains back to the soil instead of pooling in the pipe or fan |
| Fan location | Attic, garage or exterior, not inside the living space | A leak on the pressurized side of the fan should not release radon indoors |
| Discharge point | Above the roof edge, away from windows, doors and other openings | Radon concentration drops quickly with distance; ground-level discharge risks re-entry |
| Monitor | U-tube manometer or alarm on the pipe below the fan | Shows at a glance whether the fan is creating suction |
| Sealing | Caulk around the pipe penetration and major slab cracks | Reduces conditioned air leaking into the system and improves suction |
The Suction Point: Where the Layout Starts
The suction point is the foundation of the whole layout. In a typical basement or slab-on-grade home, the installer drills a core hole through the concrete and removes some soil or gravel beneath it to create a small open pit. The pipe is set into that hole and sealed to the slab.
Location is a balance of performance and practicality. A spot near the middle of the slab often allows suction to spread evenly, but a location near an exterior wall or utility area may make the pipe route much simpler. Before drilling, many installers perform a diagnostic test, sometimes called a pressure field extension or communication test, by drilling small test holes and measuring how well suction travels under the slab. That helps decide whether one suction point will be enough.
Sub-slab material makes a large difference. The EPA’s radon-resistant construction guidance describes a 4-inch layer of clean, coarse gravel below the slab as an “air flow layer” that allows soil gases to move freely beneath the house. Homes with good gravel beds may need only one suction point. Homes built on tight clay or with obstructions such as footings under interior bearing walls may need two or more.
Multiple suction points
When more than one suction point is needed, the pipes from each are typically joined with tees into a single main riser before they reach the fan. Each branch should still slope back toward its own suction point. Split-level and multi-section homes often have separate slabs with no air connection between them, and each section may need its own suction point.
Sump pits as suction points
A sump pit is often already connected to drain tile around the foundation, which can carry suction around the perimeter. Many installers seal the sump with an airtight lid and pipe from it, or tie a sump into the main system. Our guide to a radon mitigation system with a sump pump explains how the lid, pump access and suction work together.
Pipe Size, Material and Slope
The pipe itself is ordinary plumbing material. The EPA’s radon-resistant new construction guidance calls for a 3-inch or 4-inch solid PVC Schedule 40 pipe running from the gravel layer to vent soil gases outside above the house, and says the pipe should be labeled “Radon System.” Retrofit systems in existing homes commonly use the same sizes. Smaller pipe can increase airflow resistance and noise, while larger pipe allows the fan to move more air with less effort.
Fittings matter too. Every elbow adds resistance, so installers usually aim for the shortest practical route with the fewest turns. Joints are glued with PVC primer and cement so that the pipe is airtight; an air leak on the suction side wastes fan capacity, and a leak on the pressurized side above the fan could release radon.
Why the pipe slopes back
Soil gas is humid. As it travels up a pipe through a cold attic or along an outside wall in a Colorado winter, moisture condenses on the inside walls. If a horizontal run is pitched away from the suction point, that water can pool in low spots, restrict airflow, freeze or even drain into the fan housing. Installers typically slope horizontal runs back toward the suction point so condensation drains down into the soil. Vertical runs drain naturally.
Supports and penetrations
Pipe is usually secured with straps or hangers at regular intervals so it does not sag over time. Where it passes through floors, walls or the roof, penetrations are sealed and, where required, fire-stopped. Local building codes may apply, so a permitted installation reviewed by an inspector is worth asking about.
Fan Placement: Outside the Living Space
The fan is where the layout changes from suction to pressure. Below the fan, the pipe is under negative pressure, so any small leak pulls air in. Above the fan, the pipe is under positive pressure, so any leak pushes radon-laden air out. That is why fans are generally placed outside the living space, typically in one of three locations:
- Attic. The pipe runs up through the house and the fan sits in an unfinished attic, with the exhaust continuing through the roof. The attic is outside the living space, and the fan is protected from weather.
- Garage. In homes with an attached garage, the pipe may run into the garage and the fan may be mounted there or in the garage attic before the pipe exits through the roof.
- Exterior. The pipe exits the foundation wall and the fan is mounted on the outside of the house, with the discharge pipe running up the wall to above the roof edge.
The EPA’s radon-resistant construction guidance reflects this idea by recommending an electrical junction box in the attic for a future vent fan, should testing show one is needed. Placing a fan in a basement or other living area is generally discouraged for the pressure reasons above; our article on a radon fan in the basement explains the concerns in more detail. To compare fan models sized for different layouts, browse our radon fan selection.
Fans do wear out. The EPA notes that fans may last for five years or more, that manufacturer warranties tend not to exceed five years, and that a replacement typically costs around $200 to $350 including parts and labor. A layout with an accessible fan location makes that future swap easier.
Interior vs. Exterior Routing
The biggest choice in most layouts is whether the pipe runs inside the house or outside it. Both can work well when installed correctly.
Interior routing
An interior route runs the pipe up through closets, chases or a garage to an attic fan, then out through the roof. Advantages include a cleaner exterior appearance, a fan protected from weather, and a pipe that stays warmer in winter, which reduces condensation and freezing. Drawbacks include more labor, more holes in floors and ceilings, and the need for a suitable vertical path. In finished homes, finding that path can be the hardest part of the job.
Exterior routing
An exterior route takes the pipe out through a rim joist or foundation wall to a fan mounted on the side of the house, with discharge pipe running up past the eave. Installation is usually faster and less disruptive inside. Trade-offs include visibility, exposure of the fan to weather, and more condensation and potential icing in cold weather. Some installers use insulated or boxed-in enclosures or paint the pipe to blend in with the siding.
Choosing between them
The right choice depends on the house. A ranch home with an unfinished basement and an accessible attic above a utility closet may be well suited to interior routing. A finished two-story home may be far simpler with an exterior route. Cost also differs, which is covered below.
Discharge Location and Roof Clearance
Where the pipe ends is a key safety part of the layout. The EPA’s answer to why radon must be vented above the roof explains that radon concentration falls off dramatically with distance from the discharge point, approaching background levels within about 3 to 4 feet. It states that the EPA disallowed ground-level discharge mainly because of the potential for the gas to re-enter the house and the possibility of children being exposed to high radon levels.
Beyond the roof requirement, industry mitigation standards and many state programs commonly call for the discharge to sit above the roof edge and a set distance away from windows, doors, other openings and air intakes. Exact clearances depend on the standard and jurisdiction, so homeowners should ask the installer which standard the layout follows and confirm it with the local building department where needed.
The EPA also notes that radon is easily influenced by air movement and pressure, and that in homes with forced-air heating and cooling, radon can spread throughout the dwelling. That is part of why a properly sealed, properly vented system matters: the goal is to release the gas where it dilutes into outdoor air, not near a place it can be drawn back inside.
The Manometer and System Monitoring
Every active system should include a way to tell whether the fan is working. The most common is a U-tube manometer mounted on the pipe below the fan, often in a basement or utility area where it is easy to see. When the fan pulls suction, the liquid in the tube shifts so the two sides are at different heights. If the levels even out, the fan may have stopped or the pipe may be blocked or disconnected.
The EPA advises homeowners to look at the system’s warning device on a regular basis to make sure it is working, and recommends retesting the home at least every two years to confirm radon levels remain low. Some systems use an audible or visual alarm instead of, or alongside, a manometer. Our manometer gauge guide explains how to read the gauge and what changes in the reading may mean.
A manometer shows suction, not radon level. Only a radon test confirms the system is lowering radon in the living space.
Crawl Spaces, Sealing and Other Layout Variations
Crawl spaces
Homes with dirt-floor crawl spaces usually use sub-membrane depressurization. A heavy plastic sheet is laid over the soil and sealed at the edges and seams, and the suction pipe draws from under that membrane. The pipe then follows the same rules for slope, fan placement and discharge. Many Front Range homes combine a basement slab with a crawl space section, in which case the layout may tie both into one system. See our guide to radon mitigation in a crawl space for membrane details.
Sealing openings
The EPA’s radon-resistant construction guidance recommends sealing openings, cracks and crevices in the foundation floor and walls, including the slab perimeter crack, with polyurethane caulk. In a retrofit, sealing major openings helps the system by reducing the amount of indoor air the fan pulls through the slab, which can improve suction and reduce energy loss. Sealing alone is generally not considered a complete fix. Our radon seal article covers what sealing can and cannot do.
Passive stacks in newer homes
Many newer homes were built with a passive radon pipe that runs from below the slab through the house and out the roof without a fan. If a test shows elevated radon, that existing pipe can often be activated by adding a fan in the attic, which is one reason the EPA recommends an attic junction box during construction.
What Layout Means for Cost
Layout is one of the main factors in installation price. A short, simple exterior run with one suction point usually takes less time than an interior route through finished space, multiple suction points or a combined basement and crawl space system. Roof penetrations, fire-stopping, electrical work for the fan and patching finished surfaces can all add labor. For current price ranges and the factors that drive them, see our breakdown of radon mitigation system cost.
When comparing quotes, ask each contractor to describe the proposed layout: where the suction point will go, how many there will be, which route the pipe will take, where the fan will be mounted and where the discharge will end. Quotes that differ widely in price often differ in layout, and that conversation helps compare them fairly.
Checking an Installed Layout
Whether the system is new or came with a house, a few checks help confirm the layout is doing its job:
- Find the manometer and confirm the liquid levels are uneven, which indicates suction.
- Look for labels marking the pipe as part of a radon system.
- Check horizontal runs for sags or reverse slope where water could collect.
- Confirm the fan location is outside the living space and the fan is running.
- Look at the discharge from outside to see that it ends above the roof edge and away from windows and openings.
- Retest the home, ideally in the lowest lived-in level, to confirm results are low.
For related levels and test interpretation, browse our radon levels hub.
References
- Radon-Resistant Construction Basics and Techniques — U.S. Environmental Protection Agency
- Why must radon be vented into the air above my home’s roof? — U.S. Environmental Protection Agency
- How do I know if my radon mitigation system is working properly? — U.S. Environmental Protection Agency
- Radon and Your Health — Centers for Disease Control and Prevention
Frequently asked questions
What size pipe is used for radon mitigation?
Radon systems commonly use 3-inch or 4-inch solid PVC Schedule 40 pipe. The EPA describes this size for radon-resistant new construction, and many retrofit systems use the same.
Why does radon pipe slope back toward the suction point?
Soil gas carries moisture that condenses in the pipe, especially in cold weather. Sloping horizontal runs back toward the suction point lets that water drain into the soil instead of pooling in the pipe or fan.
Can a radon fan be installed in the basement?
It is generally discouraged. The pipe above the fan is under positive pressure, so any leak could push radon into the living space. Fans are typically placed in an attic, garage or on the exterior.
Where should a radon pipe discharge?
The EPA says radon should be vented above the roof and disallowed ground-level discharge because of the risk of re-entry. Mitigation standards also commonly call for distance from windows, doors and other openings.
How can I tell if my radon piping system is working?
Check the manometer or alarm on the pipe regularly. The EPA also recommends retesting your home at least every two years to confirm radon levels remain low.
Wondering whether the pipe route in your home is set up correctly? Get in touch and we can connect you with a certified Front Range radon mitigation professional.
Test your home for radon
Radon is invisible and odorless, so a test is the only way to know your level. A short-term kit gives a first reading in days; a digital monitor tracks it over time.
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 AirChek Charcoal Radon Test Kit | Lab fee usually included; EPA short-term protocol. | Amazon — $21.95 |
 First Alert RD1 Radon Test Kit | Widely stocked; 48-hour charcoal test. | Amazon — $16.98 |
 Airthings Corentium Home | Digital monitor with a long-term average. | Amazon — $147.14 |