Price
What does a house extension cost?
Usually the first question, and rightly so. We do not put a figure on this page. Not to be mysterious, but because any number without your address attached is a guess. What we do instead: explain exactly where the money goes, so you can judge the quote you eventually receive.
Two extensions of the same size can be tens of thousands of euros apart, and that difference is almost never the builder’s margin. It is in the foundation, in the glass, in the span the structure has to bridge, and in whether you get a shell or a finished room.
So it works like this: we come and look, and then you get a price per element. If it comes out too high, we can look together at what can come out (a roof light, more expensive sliding doors, the underfloor heating) rather than you receiving a lower total with no idea what was left out of it.
Want to know what it costs in your case?
Tell us what you have in mind and send a few photos. You will get a personal price indication: not a standard figure, but an estimate for your house.
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Price
What determines the price
- 01
Width and depth
More metres means more foundation, more roof and more facade, but the price does not scale in a straight line. Above a certain span the steelwork gets heavier and more expensive, and that is a step, not a slope.
- 02
Foundation and piling
The biggest unknown, and the reason we do not quote blind. On sand, a strip foundation is often enough. In parts of Amsterdam piling is required, and then the access to your back garden decides the difference between a machine that is through it in a day and hand work that takes a week.
- 03
Frames and sliding doors
Often the second-largest item. A three-panel four-metre aluminium slider with a slim profile and triple glazing costs a multiple of a standard uPVC unit. This is usually where you have the most influence without touching the structure.
- 04
Roof and insulation
A flat roof is standard; a roof light in it costs considerably more than the same area of closed roof. The insulation thickness follows from building regulations and is not a choice, but the build-up around it is.
- 05
Underfloor heating and electrics
Underfloor heating is usually sensible in an extension, but it has to connect to something. If your current boiler or consumer unit cannot carry it, that upgrade belongs in the quote, not as extra work afterwards.
- 06
Level of finish
Shell, wind- and watertight, or move-in ready. The difference between those three is the largest of all, and it is also the item most often left out to make a quote look cheap.
What our quote includes
- Structural calculations by a qualified engineer
- Drawings and, where required, the permit application
- Demolition and removal of rubble
- Foundation and, where needed, piling
- Steelwork, brickwork and facade finish
- Roof, roof covering and insulation
- Frames, glazing and sliding doors
- Electrics, underfloor heating and connections
- Plastering, painting and floor finish
- Site facilities, protective covering and daily tidying
- Handover with a snagging list and warranty terms
What it does not include
- Council fees for the permit
- The kitchen itself (we do provide the connections)
- Loose furnishing, curtains and light fittings of your choosing
- Landscaping and paving afterwards
- Unforeseen ground finds or asbestos, always discussed with you first
Payment in instalments
- A deposit on signing, no more than is customary in the trade
- Instalments tied to completed phases: foundation, shell, wind- and watertight, finishing
- The final instalment after handover and after the snagging list is cleared
Practical
Comparing two quotes
Even if you end up going with someone else: this is what to look at.
Compare the lines, not the total
Put two quotes side by side and first look for what appears in one and not the other. Nine times out of ten that explains the price difference completely.
Watch for the word “shell”
A shell means you then have to arrange a plasterer, an electrician, a floor layer and a painter yourself. That is a fine choice, but add those costs before you compare quotes.
Ask about the structural engineer
A quote without structural calculations is not a quote for an extension. Ask who produces them and whether they are included. This is the one item where cutting corners is genuinely dangerous.
Ask about the payment schedule
A healthy builder does not ask for 50% up front. Instalments should follow completed work, with a final instalment after handover.
Compare the lines, not the total.
Want to know what it costs in your case?
Tell us what you have in mind and send a few photos. You will get a personal price indication: not a standard figure, but an estimate for your house.
Free, with no obligation · Reply within 1 business day