Guide

Radon Mitigation System Types

Active sub-slab depressurization

The default, and the right answer for most poured-concrete basement slabs. A suction point through the slab, a pit beneath it, a pipe to above the roofline, and a continuously running fan. Full detail on the dedicated page. Everything below is what happens when the foundation does not fit that description.

Sub-membrane depressurization, for crawlspaces

A dirt-floor crawlspace has no slab to draw from and effectively an unlimited supply of soil gas across its whole area. The fix is to create the missing slab out of heavy polyethylene sheeting: a sealed membrane laid across the soil, run up the foundation walls and piers and sealed there, with suction taken from beneath it.

The membrane is the system. A tear, a poorly sealed seam or a section pulled up for storage access is a hole in the system. Where the crawlspace also has a moisture problem, this work overlaps substantially with encapsulation and the two are usually worth doing together. See crawlspace radon.

Drain tile depressurization

Many basements have an interior perimeter drain tile loop under the slab edge, usually discharging to a sump. That loop is already a distribution network running the full perimeter of the house, which is exactly what a suction field needs to be.

Where it exists and is intact, drawing from it is often the most effective and cheapest option, because the hard part is already installed. An exterior drain tile loop can sometimes be used the same way, though it is more variable.

Sump-integrated systems

A sump pit that connects to the drain tile can be converted into the suction point. The pit gets an airtight, gasketed lid with sealed pass-throughs for the pump's power cable and discharge line, and the suction pipe comes off the lid.

Two things go wrong with this in practice. A lid that is not genuinely airtight leaks conditioned air and wastes the fan's capacity, and a lid that cannot be removed makes the sump pump unserviceable. Both are avoidable and both are common.

Block wall depressurization

Hollow concrete block foundation walls contain a continuous interconnected void running through the cores. Radon entering the footing area can travel up inside that void and emerge through the top course, through mortar joints, or through any opening in the wall, sometimes well above floor level.

Depressurising the wall cavity itself, by drawing from the block cores, addresses that path. It is usually done alongside a slab system rather than instead of one, and the top course generally has to be capped and sealed for it to work.

Slab-on-grade and mixed foundations

A house with no basement still has soil gas under it, but the options for routing pipe change. There is no unfinished basement to run it through, so the route is typically through a closet, a garage, or up an exterior wall.

Mixed foundations are the genuinely difficult case, and they are common in older York County housing: a basement under the original structure, a crawlspace under a later addition, occasionally a slab section too. These are effectively separate soil-gas environments, and they usually need separate suction points, sometimes separate systems. This is where diagnostic testing earns its keep, and where the cheapest quote is most likely to be the one that underperforms.

What actually drives the price

Factor	Effect
Number of suction points	The single biggest driver. Each one is a core, a pit and more pipe
Existing drain tile or a usable sump	Reduces cost, the suction field is already there
Crawlspace membrane	Increases cost, materials plus awkward labour
Interior vs exterior pipe route	Interior is more labour, exterior is more visible
Finished basement	Increases cost, routing and restoration around finished surfaces
Two-storey vs ranch	Pipe length to get above the roofline
Existing passive rough-in	Large reduction, often just a fan and a manometer

Notably absent from that list: how high the test result was. A 30 pCi/L house and a 5 pCi/L house with the same foundation usually get the same system. Ranges are on what it costs, and passive vs active covers the rough-in case.

Common questions

Why did I get quoted two suction points?

Because suction does not travel well under every slab. If a slab was poured on clay or compacted fill rather than clean gravel, one point may only depressurise part of it. Diagnostic communication testing is what tells an installer this, and skipping it is how underperforming systems get built.

Is an exterior system worse than an interior one?

Not worse, different. Exterior runs keep the work out of finished space and are simpler to service, but the pipe is visible and cold weather can cause condensate to freeze in it. Interior runs are quieter and hidden but more invasive to install.

Can my sump pit be used?

Often yes. A sump already connects to the drain tile loop under the slab, so sealing the pit with a gasketed lid and drawing suction from it can mitigate the whole footprint cheaply. It has to be sealed properly, and the pump still has to work and be serviceable.