Guide

Radon in Row Homes and Attached Houses

Why attached housing is different

The mitigation physics do not change: draw from beneath the slab, hold it at lower pressure than the house, vent above the roofline. What changes is that two of the assumptions behind a standard design do not hold.

The soil does not stop at the property line. A party wall sits on a footing, and the gravel and soil beneath the slabs on either side of it are continuous or close to it. So a suction field does not respect the boundary, in either direction.

There is no side elevation. On a detached house the default cheap route is up an outside wall. On a mid-row unit there are only two exterior walls, front and rear, and one of them faces the street.

What that means in practice

• Your fan may need more capacity than the square footage alone suggests, because it is partly working on soil beyond your footprint
• An unmitigated neighbour is a reservoir your system is partly drawing from, which is not harmful but does affect sizing
• A neighbour who mitigates may reduce your levels slightly, and vice versa. Do not rely on it
• Diagnostic communication testing matters more here, because the suction field is harder to predict
• End units behave more like detached houses and are usually simpler
• Shared basement walls that are block rather than poured add the block-cavity path. See system types

Routing the pipe

Interior run

Up through a closet, a utility chase, or a boxed corner to the attic and out the roof. Usually the best answer in a row home: it keeps the street elevation clean, it keeps the pipe warm so condensate drains rather than freezing, and it is quieter. It costs more labour and it uses interior space.

Rear elevation

Up the back wall to above the roofline. Cheaper, and out of sight from the street. Check the termination clearance from the neighbours' windows as well as your own, which is a constraint that barely exists on a detached house.

Front elevation

Generally a last resort. Visible from the street on a terrace where every house faces the same way, and in some places subject to local rules, particularly in a historic district.

Termination clearances matter more here

The vent must terminate above the roofline and away from windows, doors and other openings, so the discharged gas disperses rather than re-entering. In attached housing, "other openings" includes your neighbours'. A termination that satisfies the clearance from your own windows and sits three feet from next door's bedroom window is not an acceptable installation.

This is worth raising with the contractor explicitly, because it is easy to design from a single-house habit.

Talking to the neighbours

Not a legal requirement, and usually worth doing anyway.

• If they have tested, their result is more informative about your house than a county average is, because you share soil and a wall
• If two or three adjoining units mitigate at the same time, there is often a per-unit saving on mobilisation
• A rear-elevation pipe is visible from their property, and a conversation beforehand is cheaper than one afterwards
• If the building is a condominium or has an association, exterior alterations may need approval
• If you rent, the property owner has to authorise the work. See radon testing for landlords

Testing in an attached house

Same rules as anywhere: lowest lived-in level, closed-house conditions, device 20 inches to 6 feet off the floor and at least 3 feet from exterior walls, windows and doors, undisturbed for the full period.

One addition worth knowing: a neighbour's result is weak evidence in a detached street and slightly better evidence in a row, because you share soil and structure. Better, not sufficient. Test your own. See radon testing.

What it costs relative to a detached house

Broadly similar, with two pressures in opposite directions. An interior pipe run costs more labour than a simple exterior one. Against that, row homes are often smaller footprints with simple rectangular slabs, which can mean a single suction point where a sprawling ranch needs two.

The things that actually move the number are the same everywhere: how many suction points, whether there is usable drain tile or a sump, and whether the basement is finished. See what it costs and sump pumps and radon.

Common questions

Can I mitigate if my neighbour will not?

Yes. A properly sized system in your own unit works. It may need more suction capacity than a detached house of the same size, because the slab does not stop neatly at the party wall.

Will my system pull radon from next door?

It draws from beneath the slab, and beneath a party wall the soil is continuous, so in practice it may depressurise some of the adjoining footprint too. That is generally good for both of you, and it is a reason your fan may work harder.

Where does the pipe go with no side wall?

Usually interior, up through the house to the roof, or up the rear elevation. A front elevation run is a last resort on a street of attached houses, both for appearance and often for local rules.