Part L Insulation: What Changed in 2022 and What It Means Now
The 2022 Part L uplift changed the maths on loft insulation. Here's what trade installers actually need to know.
The short version
Minimum loft U-values tightened in June 2022 and the industry is still catching up. For most refurbishments the target is now 0.16 W/m²K — that's 270mm of mineral wool in a standard joisted loft.
What this means in the van
Knauf Loft Roll 44 at 200mm gives you a starting point, but you'll need a second layer cross-laid to hit the refurb target. Stocking 200mm + 100mm together is the sensible approach.
Why trickle vents are now mandatory
Part F was updated alongside Part L. Any replacement window that serves a habitable room now needs background ventilation — that's trickle vents in practical terms, sized to 8000mm² for bedrooms and 5000mm² for most other rooms.
Common mistakes
- Stopping at 270mm loft roll and forgetting the cross-lay requirement
- Overlooking trickle vent specification on window replacement jobs
- Using standard unfaced roll in cold roof applications
Get the spec right on the quote and you avoid callbacks, failed inspections and compliance disputes.