IM Fleece airtightness tape roll with branded backing, partially unrolled

Radon, Airtightness Tape and Service Penetrations

September 16, 2026

When a pipe or cable passes through a radon barrier, the opening needs a detail that preserves the specified protection. An airtight tape may be one component of that detail, but being airtight does not, by itself, establish that a tape is suitable for a radon-protection system.

The useful starting point is the project's ground-gas design: the named membrane, its joints, its connection to the rest of the building and the treatment of every penetration. Select the accessories from that design, supported by the relevant manufacturer documentation.

Why the whole system matters

Radon is a naturally occurring radioactive gas. The UKHSA guidance on radon and Building Regulations explains that the protective measures required for new building work depend on the site's radon risk. Establish those requirements with the project designer and building control before choosing a membrane or tape.

A roll described as “fleece”, “foil” or “butyl” does not identify its complete gas-protection performance. Nor does the presence of one tested material prove that a different tape, collar or liquid coating can be substituted at its joints.

For general air-barrier connections, our airtightness tape guide covers tape selection. For ground gas, use the additional evidence and details required by the radon specification.

What to establish before ordering tape

The required protective measures for the site and proposed building work.
The exact membrane and the certification or technical assessment relevant to its use.
The approved jointing method and named accessories.
The pipe material, diameter, spacing and any expected movement.
The inspection, protection and handover requirements before the barrier is concealed.

Collect this information on one detail sheet for each penetration type. A drawing labelled only “seal around pipe” leaves the installer to decide crucial matters on site, often after the services have restricted access.

Give service penetrations enough space

A collar or top-hat detail needs space to connect to the surrounding membrane. Consider that space while routing the services, rather than after several pipes have been grouped tightly in a corner. Mark the barrier level on the coordinated services drawing so the connection is understood by every trade.

Manufacturer details demonstrate why the accessories matter. The Visqueen RadonBlok 600 technical datasheet specifies its own jointing and penetration treatments. It is an example of a defined system, not permission to use those instructions with a different membrane.

For a single pipe, check the approved collar arrangement, the membrane bond and the seal to the pipe itself. For a cluster, obtain the manufacturer's specific detail. Wrapping one strip around the outside of a bundle can leave the spaces between services unresolved.

Where airtight tape and liquid products fit

IM Fleece Airtight Tape has technical information for airtight construction details. Its fleece backing alone must not be treated as evidence of radon certification. Specify it in a radon detail only where the required compatibility and system suitability have been confirmed.

There is separate evidence for particular liquid products. The BBA certificate for Passive Purple and Airtight White includes resistance to radon, subject to the products being installed and used within its scope. That assessment should not be transferred automatically to another product or an unassessed combination.

Application requirements also matter: the current Passive Purple Internal technical sheet specifies a minimum consumption of 1.2 kg/m² for radon use. A general airtightness coverage calculation is therefore insufficient when pricing that application. Agree the complete detail and inspection method before work starts.

Inspection continues after the first installation

Plan a check before the next layer conceals the barrier, with photographs tied to locations on the drawing. Record the products used and any repairs or changes. Repeat the check where later trades cut openings, move services or damage the membrane.

A building airtightness test and a radon measurement answer different questions. UKHSA explains how to assess indoor radon through radon measurement. In an existing building with elevated levels, follow the appropriate remediation advice; a tape repair alone should not be presented as a demonstrated solution.