Cost guide
Single storey extension cost, driver by driver
A single storey extension is the most common thing we build, and the price is decided far more by the ground and the glass than by the floor area. Two extensions of identical size on the same street can differ enormously once you look at what is under them and what is across the back of them.
"We had our loft insulated and boarded. From start to finish the process was smooth, professional and stress-free. Malcolm upgraded the insulation and …"
Where the money goes, in build order
Follow the sequence and you can see your own project taking shape in the budget.
- Step 1
Groundworks and foundations
Depth is dictated by soil and trees, not by preference. Wealden clay with a mature oak nearby can more than double the concrete before a single brick is laid.
- Step 2
Shell and roof
Blockwork, cavity, insulation and either a warm flat roof or a pitched roof tied into the existing. Flat roofs with large rooflights are usually the cheaper route.
- Step 3
The opening into the house
Removing the old rear wall needs a steel and often padstones. A full width opening is more steel than a doorway, and that shows up in both material and craneage.
- Step 4
Glazing
This is where budgets swing hardest. Sliding doors, bifolds and structural rooflights are wildly different products at wildly different prices for the same hole.
- Step 5
Fit out
Screed, underfloor heating, plaster, electrics, decoration and flooring. Kitchen supply is usually separate and worth quoting separately so you can see it clearly.
Things that quietly add cost
- Poor site access, so every load of muck out and material in is barrowed by hand
- Relocating a manhole or building over a shared drain, which needs the water authority involved
- Level changes across a sloping garden, meaning retaining structure as well as a floor slab
- Party wall matters where you build up to a shared boundary
- Moving a boiler, consumer unit or gas meter that sits exactly where the opening wants to be
Where you can save without regretting it
Choose one hero element. A single generous rooflight over the dining end will do more for the room than three modest ones, and costs less to install and to detail.
Keep the drainage runs short. Positioning a utility or cloakroom near the existing stack rather than at the far corner is a free saving made at drawing stage.
Do not save on insulation, the roof covering or the steelwork. Those are the parts you cannot revisit later without taking the room apart.
What our written quote gives you
One document, one contractor, one price. Groundworks, structure, roof, glazing and finishes broken out line by line after a free site visit, backed by a 5 year workmanship guarantee and 40+ years of building across Kent.
FAQs
Common questions
Does size alone decide the price?
No. Foundation depth, the width of the structural opening and the glazing specification move the figure more than a few extra square metres do.
Are bifolds or sliding doors better value?
Sliders usually give more glass for the money and a slimmer sightline. Bifolds win when you genuinely want the whole wall open. Decide by how you will use the room, then price both.
Why does foundation cost vary so much locally?
Clay soils shrink and swell, and nearby trees make that worse, so building control may require deeper foundations. It is site specific and we assess it on the survey.
Should I get the kitchen priced separately?
Yes. Keeping the building work and the kitchen supply as separate figures makes both easier to judge and lets you adjust one without disturbing the other.
How long does a single storey extension take?
It depends on size, roof type and glazing lead times. We give you a written programme with the quote rather than a guess on the doorstep.
Can you work to a fixed budget?
Yes, if you tell us the number at the start. We will show you honestly what fits and what does not rather than start the job and squeeze it later.
Ready to price your single storey extension cost, driver by driver in Kent?
Free site visit, fixed-price written quote and a 5 year workmanship guarantee — backed by 40+ years on the tools and our workshop in Biddenden.
"We had our loft insulated and boarded. From start to finish the process was smooth, professional and stress-free. Malcolm upgraded the insulation and …"
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Free site visit, fixed price written quote, 5 year workmanship guarantee.