Above existing joists
Lightweight Screed for Loft Conversions
Loft floors are joist-limited. We pour lightweight or thin-section screed that adds acoustic performance without overloading the structure.
The problem with a loft conversion floor is weight. Standard 50mm liquid screed over UFH weighs ~110kg/m² — often more than the existing joists want to see.
The fix is either lightweight aggregate screed at half the weight, or a thin-section pour at 25–30mm over acoustic board. We spec both, depending on the structural report.
Lightweight vs thin-section
Lightweight aggregate
- 50–60kg/m²
- 50mm pour over PIR
- UFH-friendly
- Slightly softer underfoot
Thin-section over acoustic
- 70–80kg/m²
- 25–30mm bonded pour
- Better for solid feel underfoot
- Needs approved acoustic layer
What we need from the structural engineer
- Joist loading budget (kg/m²)
- Deflection limit at midspan
- Any noggin or additional bearing detail
- Confirmation acoustic board is included in the deck build-up
Frequently asked
Loft floor to spec?
Send the SE report or joist details and we'll come back with a build-up that meets the loading and acoustic spec.