Domestic Project Types
Liquid Screed for Single-Storey Rear Extensions
A rear extension usually means matching a new floor build-up to an existing house level while adding underfloor heating, so junction detailing and depth planning matter more than raw floor area.
Rear extensions are one of the most common jobs we're asked to price, and the technical challenge is rarely the pour itself — it's tying a new insulated, heated floor into an existing house that was built to a different specification decades earlier.
Because the extension floor usually needs to finish flush with the existing kitchen or hallway, insulation thickness and screed depth have to be worked out early, often before the groundworker sets out the slab. Getting this sequence wrong is one of the most common causes of a last-minute redesign, since once the slab is cast the room for adjustment shrinks considerably.
The build sequence on a typical rear extension runs from groundworks and slab through to insulation, membrane, underfloor heating pipe, then screed, followed by plastering and floor finishes. We sit roughly in the middle of that chain, which means our pour date depends on the groundworker and heating installer finishing on time, and the plasterer and flooring contractor waiting on us in turn. A short delay upstream can compress the whole back half of the programme, so we keep in regular contact with the builder rather than simply turning up on a fixed date regardless of site progress.
Planning a rear extension floor?
Send us the extension drawings and we'll advise on build-up, insulation depth and screed specification before the slab goes down.
Or call our landline on 01392 237700
Matching levels with the existing house
Before the slab is cast, we work with the builder to confirm the finished floor level against the existing internal doorway or step. This dictates how much insulation can go in and how thick the screed needs to be to still take a chosen floor finish without a step forming.
Where an existing solid floor has less insulation than current practice would specify, we'll flag the trade-off between thermal performance and keeping floors flush, since raising the whole ground floor is rarely practical on a single extension.
Underfloor heating in a small addition
Most rear extensions have room for one or two heating zones. Pipe centres and manifold position are agreed before the pour, and pipes are fixed down securely so they don't float during placement.
Because the area is small relative to a whole-house scheme, commissioning and the initial heat-up are usually straightforward, but we still follow a gradual warm-up schedule rather than switching straight to full temperature.
Where a rear extension sits in the build sequence
On most domestic rear extension jobs, the running order is groundworks and slab, then first-fix plumbing and electrics through the new walls, insulation and DPM, UFH pipe, and only then the screed pour. We ask to see the site, or at least clear photos, before committing to a date, since any of these earlier trades running late pushes our slot back.
After the pour, plastering typically follows once the screed has taken its initial set, with kitchen fitting, tiling or timber flooring coming later once moisture readings confirm the floor is ready. Coordinating this handover directly with the builder avoids the awkward situation of a kitchen delivery arriving before the floor can safely take the units' weight.
Common pitfalls on rear extension floors
The most frequent issue we see is a threshold level agreed too late, after the slab has already been cast at a height that leaves no room for the intended screed depth. Confirming finished floor level at the design or planning stage, not on the day of the pour, avoids this.
A second common pitfall is under-specifying the manifold cupboard or leaving no route for the flow and return pipes to reach it, which then has to be retrofitted through a finished wall. Agreeing the manifold location with the heating installer before first fix removes this risk entirely.
Single-Storey Rear Extension — the points that decide it
Single-Storey Rear Extension — your questions
In short
A rear extension usually means matching a new floor build-up to an existing house level while adding underfloor heating, so junction detailing and depth planning matter more than raw floor area.
Planning a rear extension floor?
Send us the extension drawings and we'll advise on build-up, insulation depth and screed specification before the slab goes down.