Which Approved Documents apply
Three Approved Documents drive most glazing jobs. Part L covers thermal performance, Part F covers ventilation, and Part Q covers security on new dwellings and material changes of use. Windows and external doors are controlled fittings, so the work is notifiable whether you self-certify under a competent person scheme or go through building control.
Get the split clear before you quote. Replacement work in an existing dwelling is governed by Part L and Part F. New build and change of use pull in Part Q as well. Confirm which applies on site, because the standards differ and the wrong assumption shows up at completion.
Work to the editions current at the time of the application. The Future Homes and Buildings Standards bring revised Parts L and F, with the regulations coming into force in 2027 and transitional provisions running beyond that. Check the commencement and transitional position before you specify. We hold UKCA marking and DoP support for the systems we fabricate.
Part L: hitting the U-value
For replacement windows and doors in an existing dwelling, the limiting standard is a whole-unit U-value of 1.4 W/m2K, or a Window Energy Rating of band B or better. That figure is for the whole window, frame and glass together, not the centre-pane glass alone. Specify against BS EN 14351-1 so the declared performance is the one building control will accept.
Thermally broken aluminium is what gets a slim frame to that number. The polyamide break separates inner and outer faces, so a warm-edge spaced double or triple glazed unit can carry the whole assembly under the threshold. Ask for the system U-value at the actual size, since small units read worse than the test reference size.
Part F: don't choke the ventilation
Replacing windows tightens the building. Part F requires that ventilation is no worse after the work than before, which in practice means background ventilators in the new frames where they existed or are needed. Background ventilator sizing is given as an equivalent area in mm2, not a free area, so check the figure against the test data for the vent.
Trickle vents are the usual route. Factor them in at quote stage, because retrofitting after a flush install is awkward and the airflow path through the frame has to be designed in. If a room already has a compliant background ventilator elsewhere, you may not need to add one to the window. Confirm the required equivalent area against the current Approved Document F before you order.
Part Q and certifying the work
Part Q only bites on new dwellings and material changes of use, not straight replacement in an existing home. Where it does apply, the doorset and accessible windows must follow a PAS 24 product route. We can supply PAS 24 product routes across the door range.
Whichever path you take, the paperwork is the deliverable that closes the job. We support the documentation trail behind every order.
- Self-certify through a competent person scheme such as FENSA or Certass, or notify building control directly before you start.
- Issue the building regulations compliance certificate to the client and keep the Declaration of Performance on file.
- On new build and change of use, specify doors and accessible windows to a PAS 24 product route to meet Part Q.
- Confirm the doorset detailing required by Part Q is specified where it applies.