Airtightness at junctions and connections is one of the most consistently underperforming aspects of modern construction — and one of the most consequential. With Building Regulations Part L tightening and energy performance under increasing scrutiny, the way connections are sealed across the building envelope is no longer a peripheral detail. It’s a compliance issue.
Lynvale’s ACT (Acrylic Connection Tape) is designed specifically to address this.
The problem with junctions
A building envelope can be well insulated, well designed, and well built — and still fail its airtightness test because of poorly sealed junctions. Connections between boards, around window and door frames, at penetrations, and where different materials meet are the points where air leakage most commonly occurs.
These aren’t always large gaps. Even small, inconsistent seals at connections accumulate into meaningful air leakage across a whole building — undermining energy performance, creating condensation risk, and in many cases preventing compliance with Part L targets.
The challenge is that these junctions involve a wide variety of substrates — timber, CLT, light gauge steel, masonry, concrete, PVC, glass — often in the same building. A tape that works on one substrate may not perform on another, and site conditions add further complexity.
What ACT does differently
ACT is an acrylic-based connection tape that seals and bonds in a single process — eliminating the need for separate adhesion and sealing steps and saving time on site without compromising performance.
Key performance characteristics:
Regulatory compliance — ACT is compliant with both Part L and DIN 4108-11, meaning it meets the airtightness requirements demanded by UK Building Regulations and the German standard that underpins much of the Passive House and high-performance construction specification world.
Substrate versatility — ACT bonds effectively across timber, CLT, LGSF, masonry, concrete, PVC, and glass, making it suitable for mixed-substrate junctions that are common in both retrofit and new build.
Cold weather performance — usable in temperatures down to -20°C with frost resistance to -40°C, ACT can be applied in conditions that rule out many alternative products. No drying time required.
Movement resistance — buildings move. ACT offers exceptional resistance to dynamic shear and thermal movement, maintaining a permanent elastic seal across connections that expand, contract, and settle over time.
Humid condition performance — particularly relevant for vapour control layer connections to concrete and other awkward substrates where moisture is a factor during and after construction.
Where ACT is specified
ACT addresses the full range of connection and junction sealing requirements across the building envelope:
- Board-to-board connections in timber and CLT construction
- Airtight sealing around window and door frames
- Glazing connections and curtain wall junctions
- Pipe and service penetrations through airtight layers
- Vapour control layer laps and connections to concrete substrates
- Any junction where a permanent, elastic, airtight seal is required
Designed to last
ACT is not a temporary or interim solution. It is designed to maintain its performance over the lifetime of the building — which matters when the integrity of an airtight layer depends on every connection remaining sealed for decades.
ACT is available on NBS Source, making specification straightforward for architects and designers working within a standard specification workflow.
If you’re working on a new build or retrofit project and want to understand whether ACT is the right solution for your junction detailing requirements, get in touch with the our team.
