Extension and refurb jobs get priced on the back of a fag packet more than almost anything else in the trade. The drawings are often thinner than a new build, the client wants a number quickly, and there's a temptation to price it off experience and a walk round the property rather than measuring it properly. That works fine right up until the ground's opened up or the existing structure turns out to be worse than it looked.
Pricing extension and refurb jobs well isn't about knowing more than the next builder. It's about separating what you can measure from what you genuinely can't, and treating each one honestly.
Why these jobs are harder to price than they look
A new build gives you a clean set of drawings and a site with nothing in the way. An extension or refurb gives you an existing building to tie into, structure you can't fully see until it's opened up, and services that were never drawn accurately in the first place. Pricing that by feel means you're absorbing whatever the walls turn out to hide.
There's also the work nobody draws. Protecting the parts of the house the family is still living in. Temporary works while an opening is formed. Moving a boiler or a soil stack that happens to sit exactly where the new doorway goes. Making good to decorations in rooms the drawings don't even show. On a new build, most of that simply doesn't exist. On a domestic extension, it can be a real slice of the job.
Measuring it properly instead of pricing by feel
The fix isn't more experience; most contractors pricing these jobs already have plenty of that. It's measuring what's actually shown on the drawings, item by item, rather than pricing the whole job as one lump figure based on a similar extension from last year. Groundworks, structural openings, first and second fix, external works, all measured separately so the price reflects this job, not an average of the last five.
A typical measured breakdown for a rear extension with some internal alterations might run something like this:
- Demolitions and strip out. What comes down, what gets taken out and how it leaves site.
- Substructure. Excavation, foundations, below-ground masonry and the ground floor slab, measured from the drawing rather than assumed.
- Drainage. New runs, connections to the existing system and any manholes, measured in actual lengths.
- Superstructure. External walls, openings, lintels and steels, roof structure and coverings.
- Alterations to the existing building. Forming the opening, temporary support, making good where old meets new.
- Internal finishes and fixes. Plastering, flooring, joinery, first and second fix services.
- External works. Paving, reinstatement and anything outside the footprint that the job disturbs.
Once each of those has a quantity, the rates you apply stop being a guess about the whole job and start being a judgement about each part of it. That's a much easier judgement to get right.
Measure everything you can see. Then the allowance for what you can't see can be small and honest, not a cover for the rest.
What to build in for the parts you can't see yet
Every refurb has an element you genuinely can't quantify until it's opened up: what's behind that wall, what state the existing drainage is in. That's not a reason to guess the whole price. It's a reason to measure everything you can see properly, so any provisional allowance you carry for the unknown parts is a small, honest figure sitting on top of a solid number, not a cover for not measuring the rest of the job at all.
Name those allowances clearly on the quote. "Allowance for making good to existing floor where partition removed, subject to condition once exposed" tells the client exactly what they're paying for and why the figure might move. A vague line called "contingencies" tells them nothing, and invites them to ask you to take it off.
Where pricing extension and refurb jobs goes wrong most often
The same few traps come up again and again on domestic work:
- Pricing from the floor area. Two extensions of the same size can differ enormously once foundations, drainage and roof form are measured.
- Forgetting the tie-in. The junction between new and existing is often the most labour-intensive part of the job and the least drawn.
- Skipping the site visit. Access down a narrow side passage or a lack of parking changes the cost of every delivery.
- Carrying one big contingency. A single unexplained figure is the first thing a client asks you to cut, and then you've got nothing for the real unknowns.
Getting the drawings measured
Send us whatever you've got, plans, sketches, or a scheme drawing, and we'll measure the job to NRM2 and price it on current UK rates, local to the job, so the bulk of the job is priced from measured quantities and only the genuinely unknown parts are left as an allowance. The fee is fixed and agreed before we start.
If you're doing a lot of domestic work, our piece on estimating a loft conversion or extension covers the particular quirks of roof space jobs as well.
A rule of thumb before you send the quote
Look at your price and ask what share of it is measured and what share is allowance. If most of the number sits in lines you could explain with a quantity and a rate, you're in good shape. If a big chunk of it sits in "sundries", "extras" or "contingency", you haven't priced the job yet, you've estimated your nerve.
That's the whole discipline of pricing extension and refurb jobs in one sentence. Measure the bulk, name the unknowns, and keep the two apart so the client can see which is which. It also makes the conversation easier when an allowance does get used, because nobody's surprised.
Send your drawings before you quote the next extension or refurb, and price it from quantities instead of a walk round and a gut feel.