Glazpartners 2025
Why we need to talk about trickle vents
Dale Pegler, Technical Director at CAB, asks if trickle vent installation needs to be adapted in the face of a growing number of call backs for cill, and plaster moisture-related failures?
Since the introduction of compulsory trickle vents in new build applications under Part F in June 2022, We’ ve seen a steady increase in the number of installation issues being reported by our members. It’ s raising serious concerns and I believe we may be sitting on a ticking time bomb.
While trickle vents are also required in some replacement applications, it’ s the growing volume of remedial site callbacks to new build schemes in particular that’ s sounding alarm bells.
Installers are being asked to return to jobs to address moisture-related problems, issues that range from damaged cill boards and internal plasterboard to oxidisation of internal aluminium profiles.
We’ re starting to spot patterns. These issues are more common in the winter months when there’ s more moisture in the home, and the outside air is cold. That’ s no coincidence.
I want to be clear that what I’ m about to say is, at this stage, a theory. But it’ s an increasingly plausible one.
We believe that the cut-outs for trickle vents may be allowing external air to circulate around the perimeter of the window frame. That air may then act as a cold bridge to the internal aluminium profiles leading to condensation, and in turn, moisture-related damage.
Part F has been controversial from the outset. It mandates cutting through energy-efficient windows to achieve background ventilation. For new and replacement windows, where no vents previously existed, we now need to achieve 8,000mm ² EA in kitchens and habitable rooms, 4,000mm ² in bathrooms and none in WCs or utility rooms.
It’ s a well-intended regulation, but we’ re beginning to see the unintended consequences.
Here’ s the real worry. This isn’ t always an immediate problem. Moisture damage can take time to become visible. That means every window we’ re installing right now could be hiding an issue that won’ t appear until well down the line.
We’ re already talking with trickle vent manufacturers and exploring potential solutions. Leading trickle vent manufacturers already have a number of potential solutions available, but they aren’ t necessarily being adopted as part of the standard installation process. To find the right solution, however, we need to confirm what’ s causing the problem.
We’ re calling on installers to share their experiences. If you’ ve encountered moisture-related issues linked to trickle vent installations, we need to hear from you. Your input will be critical in helping us develop a full and accurate picture. We want to understand when and where these problems are occurring, and why.
To be fair, not every issue will stem from the vent design. In some cases, poor installation may be the culprit. But I strongly suspect that we’ re dealing with something more systemic. That’ s why we’ re collating evidence, building a dataset, and doing the investigative work now- before this becomes a much wider problem.
The good news? If we can pin down the root cause, the fix doesn’ t have to be expensive or complicated. It could be as simple as sealing the vent to prevent cold air from escaping down the profile channels or adjusting drainage.
But first, we need answers. And we need the industry to work together to find them.
For more information visit www. c-a-b. org. uk. Alternatively email enquiries @ c-a-b. org. uk or call the team on 01453 828851.
GLAZPART. COM SEPTEMBER 2025
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