Blower door testing finds the same leaks in building after building. Service penetrations are consistently near the top of the list, and unlike most air leakage paths they are entirely preventable with about twenty minutes of work per building.
A penetration is a hole in a control layer with something passing through it. Sealing it means bridging between two dissimilar materials, usually a flexible membrane and a rigid pipe or cable, in a way that survives movement, temperature cycling and decades of service.
Three things make it harder than it looks. The gap is often irregular. The pipe moves relative to the structure with thermal cycling. And penetrations are usually made by a trade who is not thinking about the envelope, at a stage when the person who cares about it is not on site.
That last one is the real problem. The plumber drilling through the ceiling plane on a Tuesday is not the person who will be explaining the blower door result on a Friday.
Ceiling plane. The worst offender in most buildings. Downlights, exhaust fans, plumbing vents, wiring drops, ceiling hatches. The ceiling is also where stack pressure is highest, which means a hole there leaks more than the same hole in a wall.
External walls. Taps, gas lines, air conditioning penetrations, electrical entries, waste pipes.
Floor. Plumbing entering through slabs or subfloors.
Between conditioned and unconditioned spaces. Garage walls, roof spaces, subfloors. Easily forgotten because they are not external, but the air on the other side is unconditioned and often humid.
Grommets are the right answer for pipes and cables. The grommet stretches over the penetration and seals against it, then the flange seals to the membrane.
This is faster than hand-taping and considerably more reliable, because a circular penetration taped by hand almost always leaves a small gap where the tape has to fold. Those folds are where the leak is.
Size the grommet to the penetration. Oversized grommets rely on the flange seal alone, which is not what they are designed to do.
For cable bundles, seal individual cables where possible. A bundle sealed as a group has air paths between the cables that a single grommet does not address.
For rectangular or irregular penetrations, work from the bottom up so each element sheds onto the one below.
Cut the membrane neatly rather than tearing it. A clean cut gives you an edge to seal to.
Where the gap is wide, back it before taping. Tape bridging a large void has nothing to press against and will fail under pressure.
Prime the substrate if it is masonry, concrete, fibre cement or dusty. This is not optional on those materials.
Where multiple services penetrate close together, sealing each one individually is slow and produces a patchwork of overlapping tapes that is difficult to inspect.
The better approach is a sealed service board: a rigid panel sealed to the membrane, with the services passing through grommets in the board. It gives you one seal to the membrane instead of six, and it is easy to check.
The practical answer to penetrations is not a product, it is a sequence.
Set the rule early. Anyone penetrating a control layer seals it, or flags it. This needs stating at the start of the job, not after the blower door test.
Do a penetration walk before closing up. Once linings go on, an unsealed ceiling penetration is a wall demolition to fix.
Keep grommets and tape on site. If the sealing kit is in the ute and the plumber is on the roof, the penetration does not get sealed.
Photograph before closing. Same reason as the wrap: it is the only record.
In retrofit work, penetrations are usually the highest-value air sealing available, particularly at the ceiling plane.
The ceiling of an existing house typically has dozens of penetrations, many of them downlights, and sealing them from within the roof space is achievable without disturbing the finished ceiling. It is often the single most effective retrofit measure by cost.
A sealed penetration should be continuous, with no visible gap at any point around the circumference. It should be tolerant of movement, which means the seal is flexible rather than rigid. It should be inspectable, meaning someone can look at it and see that it is sealed. And it should be documented.
If you cannot tell by looking whether a penetration is sealed, treat it as unsealed.
