Part L · F · M · B
Building Regulations, in plain English
Replacing windows or doors in England touches four parts of the Building Regulations. Here's what each one covers, and how our Reynaers systems are specified to meet them.
Replacing windows or doors in England touches four parts of the Building Regulations. Here's what each one covers, and how our Reynaers systems are specified to meet them.
Part L sets the minimum energy-efficiency standard for replacement windows and doors. Since June 2023, the backstop whole-window U-value for replacements in existing homes is 1.4 W/m²K or lower — installers must be registered with a Competent Person Scheme such as FENSA or CERTASS, and must issue a compliance certificate (including the whole-window U-value) within 10 working days of installation.
Modern replacement windows are far more airtight than the originals, so Part F requires background ventilation (typically trickle vents) to be maintained or added when windows are replaced.
Kitchens, bathrooms and other wet rooms often need extra provision — your installer will assess this as part of the survey.
We factor ventilation requirements into every quote, so there are no surprises once your FENSA certificate is issued.
Part M favours level access at entrance doors, particularly for new dwellings and extensions — our sliding and bi-folding systems can be specified with low-threshold options.
Where Part M applies, entrance doors need a minimum clear opening width so the door is usable by all occupants and visitors.
Part M mainly bites on new dwellings and extensions rather than like-for-like replacements — we'll flag if it applies to your project.
Habitable rooms (bedrooms and, in many houses, ground-floor living rooms) generally need at least one window suitable for emergency escape, unless there's an alternative escape route. The commonly applied minimum standard is:
Speak to our team — we'll walk you through exactly what your installation needs to comply with, at no cost.
Call 01794 721 100