Project Type
Liquid Screed for Loft Conversion Floors
Loft conversions call for careful attention to floor weight and depth, and lightweight liquid screed formulations can help keep the build-up within the available headroom.
Loft conversion floors sit above habitable rooms and directly beneath sloping roof ceilings, which makes both weight and depth particularly important considerations. Traditional deep sand and cement screeds can add unwelcome load to the existing joists and eat further into the already limited headroom typical of a converted loft, so lightweight liquid screed formulations are often specified instead.
As with any first-floor application, the design needs to reflect the structural engineer's assessment of the existing joists and any strengthening works being carried out as part of the conversion. Acoustic performance between the new loft rooms and the floor below is another factor that influences the specified build-up, particularly where the loft is being converted into a bedroom.
We work closely with loft conversion specialists and structural engineers to confirm the right screed type and depth for each project, since requirements can vary considerably depending on the age and construction of the existing roof structure.
Managing weight on existing structures
Loft conversion floors are usually built off strengthened joists designed specifically to take the additional load of habitable use. We work to the structural engineer's specification for the floor build-up, using lightweight screed formulations where they've been specified to help keep the overall dead load within the design allowance.
Fitting within limited headroom
Roof pitches and existing rafters often limit the depth available for the floor build-up in a loft conversion. We calculate screed depth carefully against the space allowed in the design, coordinating with any insulation and acoustic layers specified beneath it.
Loft Conversion Floor — the points that decide it
- Lightweight screed formulations available to reduce load on existing joists
- Depth designed to suit the limited headroom typical of loft conversions
- Follows structural engineer's assessment of existing floor joists
- Can contribute to acoustic separation between the loft and rooms below
- Suited to sloping-ceiling layouts and irregular loft floor plans
- Coordinated with loft conversion specialists on sequencing and access
Converting a loft?
We'll help you get the floor build-up right within your headroom and structural design.
Or call our landline on 01392 237700
Loft Conversion Floor — your questions
In short
Loft conversions call for careful attention to floor weight and depth, and lightweight liquid screed formulations can help keep the build-up within the available headroom.
Converting a loft?
We'll help you get the floor build-up right within your headroom and structural design.
Lightweight Screed for Loft Conversions
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