Service penetrations: the pre-air-test checklist

10 de noviembre de 2026

Air tests are rarely failed by the big, obvious things. They are failed by dozens of small holes nobody went back to: the waste pipe behind the kitchen units, the cable through the loft hatch frame, the soil stack nobody sealed at the ceiling. This checklist is for the week before the tester arrives, while those holes can still be reached.

When to check

The best time is after first fix and before plasterboard, when the airtight layer and every penetration through it are still visible. A mid-build pre-test at this stage, even an informal one, is the cheapest insurance you can buy. PAS 2035 recommends a mid-works test in retrofit for the same reason. Our airtightness testing guide explains how tests are run.

Tools

A smoke stick, to see air moving at each penetration when the house is depressurised.
A torch and a phone camera.
A penetration schedule or marked-up drawings, if you have them.
Sealing materials on hand, so leaks get fixed while you find them.

The checklist

Kitchen

Sink waste and water supplies through the wall or floor, often behind units
Cooker hood extract duct
Dishwasher and washing machine wastes
Gas supply, if present

Bathrooms and WCs

WC soil connection through the floor
Bath and shower wastes, including those hidden behind bath panels
Extract fan ducts
Soil and vent pipe at floor and ceiling level

Plant room, utility and garage

Heat pump flow and return, and their insulation
Condensate drains
MVHR intake and exhaust ducts
Incoming water main, electricity and data, including the inside of any ducts
Boiler or stove flue, which needs a temperature-rated detail, not a standard grommet
Tumble dryer vent

Loft and top-floor ceiling

Soil stack through the ceiling
MVHR supply and extract ducts through the ceiling membrane
PV and aerial cables
Downlights and pull cords, if they cross the airtight layer

Everywhere

Redundant holes from removed pipes, old vents and abandoned cables
Cable ducts and conduits that are open inside
Anything sealed only with expanding foam or silicone

What good looks like

For each penetration, you should be able to say yes to all of these:

The seal is bonded to the airtight layer itself, not just to plasterboard or a finish.
It goes all the way round the pipe, with no creases, gaps or lifted edges.
It is flexible, so the pipe can move without breaking it.
Any duct or sleeve is sealed inside too.
It is photographed with its location, for the BREL report or your retrofit record.

Where you are relying on foam, silicone or wrapped tape, plan to replace it. A sized airtight grommet suits single round pipes and ducts. A liquid grommet such as The GOAT suits bundles, corners and existing pipes. The liquid membrane fitting guide shows how to join either one into the airtight layer.

On test day

Brief every trade on site. One open window or a newly drilled hole can fail the test.
Temporary sealing of intentional openings, such as extract fans, trickle vents and MVHR valves, is done by the tester to the test standard. Do not permanently seal them yourself.
Keep waste traps filled with water, or the drainage becomes a leak.