What This Requirement Covers
Loft insulation is the simplest and most cost-effective way to reduce heat loss from a dwelling. The current recommended depth is 270 mm of mineral wool (or equivalent). For new dwellings, the loft insulation must achieve the Part L U-value requirement of 0.16 W/m2K.
Key Requirements
Current Standards
- New dwellings: Roof insulation at ceiling level must achieve a U-value of 0.16 W/m2K (typically 300-400 mm of mineral wool)
- Existing dwellings: The recommended depth is 270 mm of mineral wool (100 mm between joists + 170 mm cross-laid over joists)
- For other insulation materials, the thickness depends on the thermal conductivity (lambda value)
Installation Requirements
- First layer of insulation is placed between the ceiling joists (typically 100 mm)
- Second layer is laid perpendicular across the joists (typically 170 mm)
- Insulation must be continuous with no gaps at edges, around pipes, or at access hatches
- Do not compress insulation; it reduces its effectiveness
- Do not block eaves ventilation; use proprietary eaves ventilation trays to maintain airflow
- The loft hatch must be insulated and draught-stripped
Ventilation
- Cold roof voids (insulation at ceiling level) must be ventilated to prevent condensation
- Minimum ventilation: equivalent to a 10 mm continuous gap at opposite eaves (for pitched roofs over 15 degrees)
- For roofs with a pitch below 15 degrees, additional ventilation at the ridge is required
- Ensure insulation does not obstruct eaves ventilation
Practical Compliance Tips
- Topping up loft insulation is a simple DIY job for most homeowners; mineral wool rolls are widely available
- Wear protective clothing, gloves, and a dust mask when handling mineral wool
- Do not lay insulation over electrical cables; either clip cables to the sides of joists or route them above the insulation
- Insulate the loft hatch; an uninsulated hatch is a significant heat loss point
- If you need to use the loft for storage, install a raised platform above the insulation so it is not compressed
- Do not remove old insulation unless it is damaged; adding new insulation on top is effective
- Keep receipts for insulation materials for future EPC assessments