Sealing Gaps and Penetrations Airtight with a Passivhaus Sealant
Even on a well-membraned building, the last few millimetres around pipes, cables and frame gaps decide your air test. A dedicated airtight sealant closes them — and keeps them closed as the building moves.
The problem
Standard mastics crack, shrink or fail to bond to the mix of materials found at penetrations and frame gaps — leaving small but persistent leaks that undermine the whole airtight strategy. In a Passivhaus or low-energy build targeting 0.6 ACH or a tight Part L figure, these details can’t be left to chance.
The solution: a Passivhaus airtight sealant
Passivhaus Airtight Sealant is a flexible, high-grab sealant that bonds to common substrates and stays elastic, sealing gaps and penetrations as part of the airtight layer — alongside IM Fleece Tape for frames and board joints and brush membrane for larger junctions.
Where to use it
- Around pipes, cables and service penetrations
- Frame-to-structure gaps
- Joist ends and small structural gaps
- Anywhere a flexible airtight bead is needed
Benefits
- Flexible, durable airtight seal
- Strong adhesion to mixed substrates
- Designed for Passivhaus-level airtightness
Frequently asked questions
How is it different from normal silicone? It’s formulated for airtightness — high grab, stays flexible, and bonds across the mixed materials found at junctions.
Can it be painted? Check the product page for overpainting guidance before finishing.
See where it fits in How to Make a Building Airtight.