PART F · Ventilation
Do replacement windows need trickle vents
Replacement windows often need background ventilation, commonly provided by trickle vents. The correct approach depends on the existing ventilation system and the applicable guidance. A blanket claim that every window needs the same vent, or that vents are never needed, is unreliable.
Why changing windows affects ventilation
New windows may be more airtight than the units they replace. That can reduce an existing route for incoming air. Part F requires the ventilation implications of replacement work to be considered.
If existing windows contain background ventilators, their function needs to be accounted for in the replacement design. Where they do not, the guidance provides ways to demonstrate appropriate provision without simply assuming no action is needed.
What if I have mechanical ventilation
The type of mechanical system matters. Continuous mechanical extract and balanced supply-and-extract systems do not necessarily use the same background ventilation arrangements.
Tell the window supplier what system the home has. Ask the designer or competent installer to explain how the replacement windows fit that system.
Can another measure be used
An appropriate alternative may be possible, but it needs a clear justification. A window's ability to open does not automatically provide the same function as designed background ventilation.
For example, promising to leave windows partly open may not answer how a bedroom receives suitable ventilation in normal use.
What should the quotation say
It should identify the proposed ventilation provision, relevant performance information and certification route. Review vent positions and operation before ordering.
Ask how noise and draught concerns can be addressed through suitable design rather than by blocking the ventilation afterwards. Keep the installation and compliance records.
Check the applicable edition at the time of the work. Published 2026 ventilation guidance has its own commencement arrangements and should not be treated as immediately replacing every existing project standard.