Residential work (extensions, refurbishments, loft conversions) gets treated by some estimating services for builders as an afterthought behind commercial contracts. It shouldn't be. Estimating for residential builders has its own pressures: margins just as tight, clients who ask far more questions, and drawings that often leave more unsaid than a commercial tender pack would.
Get it wrong on a commercial job and you have a difficult conversation with a QS. Get it wrong on a domestic extension and you have a difficult conversation with a family who are living in the house while you build.
Domestic jobs still need a full measured breakdown
An extension has groundworks, structure, finishes and services just like a bigger job, only compressed into a smaller footprint. Measuring it properly to NRM2 means nothing gets missed just because the job is domestic in scale.
Think about what a typical single-storey rear extension actually contains. Excavation and foundations. Drainage, often with a new manhole or a diverted run. Cavity walls, a roof structure, a flat roof covering or tiles. Openings for bifolds or sliders, lintels, and very often a steel where the old rear wall comes out. Then electrics, heating, plastering, flooring, decoration, and the making good where new meets old. None of that is exotic. All of it has to be counted.
The trap is that residential jobs feel familiar. You've done enough of them to have a sense of the cost, so the temptation is to price the headline and move on. That works right up until the job with the awkward drainage or the party wall issue, which is usually the one you won.
What estimating for residential builders should cover
A good residential estimate is less about volume and more about not leaving anything out. Before a price goes to a homeowner, check it covers these:
- Below ground. Foundations, drainage and any ground conditions the drawings or the structural engineer flag. This is where domestic jobs most often go over.
- Structure and openings. Steels, padstones, lintels and temporary works for any wall being removed or opened up.
- The connection to the existing house. Toothing in, making good, flashings, and the finishes that have to match what's already there.
- Services. Extending heating, new circuits, and whether the existing boiler and consumer unit can actually take the extra load.
- Finishes to the specification. Floor finishes, sanitaryware, kitchen allowances, all priced to what's specified rather than a generic mid-range guess.
- Preliminaries. Skips, scaffold, welfare, protection to the parts of the house the family are still using.
Some of those lines are small. Put together, they're often the difference between a job that makes money and one that just keeps you busy.
The client wants to see where the money goes
Clients commissioning residential work often ask more questions about the breakdown than a commercial client would. It's their house and usually their savings. They'll compare your price with two others, and if yours is a single figure while a competitor's is itemised, you're the one who has to explain yourself.
An itemised estimate answers those questions before they're asked. It also makes the conversation about value rather than price. When a homeowner can see that the kitchen allowance, the steel and the drainage are all separate lines, they can make choices (a different worktop, a simpler roof light) without assuming the whole number is padded.
A homeowner who can see where the money goes argues about the specification. A homeowner who can only see a total argues about you.
Priced on rates that fit a residential specification
Fixtures, finishes and small quantities matter more, proportionally, on a residential job. A commercial rate book assumes volume: long runs of partition, repeated floor plates, bulk deliveries. A residential job has a few square metres of this and a couple of metres of that, with a delivery charge on each.
Pricing on real, current rates for the job's location, rather than a commercial-scale rate book, keeps the estimate honest to what the job actually needs. It also stops you being undercut on paper by someone who's priced the kitchen at trade volume and will find out the hard way.
At MPE every element is measured off your drawings to NRM2 and priced on current UK rates, local to the job, for a fixed fee agreed before we start. The estimate comes back through the client portal before your deadline, laid out so you can check it, add your margin and hand it on.
Where residential estimates usually go wrong
It's rarely the big items. The steel gets priced. The roof gets priced. What slips is the connective tissue: the making good, the extra length of drainage, the second fix nobody measured because it seemed obvious. On domestic work those small misses are a bigger slice of the contract than they would be on a school or a warehouse.
Then there are allowances with no description. A line that just says "kitchen allowance" with a figure beside it invites trouble. Does it include appliances? Worktops? Tiling behind the units? Spell out what each allowance covers and the homeowner can make an informed choice, instead of discovering the gap halfway through the job.
The other common problem is pricing from an early drawing. Homeowners change their minds. If your estimate doesn't say which drawing revision it was built from, you'll struggle to price the change when the kitchen moves to the other wall.
A quick check before you send the price
Read your estimate as if you were the homeowner. Can you find the drainage? The steel? The protection to their hallway? If a careful client couldn't find a line for something they know is happening, either it's missing or it's buried. Either way, fix it before they ask.
That habit of reading the price the way the client will is most of what good estimating for residential builders comes down to.