Your Builder’s Quote Is a Love Letter to the Shell (Read the Fine Print)

The Quote That Made Me Swear Out Loud I once sat with a couple who had three quotes for the same house. The lowest was £40k under the others. They were thrilled. I was suspicious. One glance at the schedule showed the cheap one had simply “forgotten” the entire foul-water drainage run to the street, plus the scaffold hire. That’s not a bargain; that’s a trap. In my experience, the difference between a good quote and a bad one is rarely the price per square metre—it’s the invisible line items that make or break your sleep.

The Shell Isn’t Sexy, But It’s Greedy Here’s the number nobody tells you at the kitchen table: the weather-tight shell—foundations, external walls, roof, windows, and doors—will swallow roughly 55-60% of your total turnkey budget. That’s before you pick a single tile. I’ve seen clients gasp when I explain that their beautiful oak staircase is 2% of the build, while the concrete under their feet is 15%. If your quote shows the shell at 40%, someone’s either using substandard materials or they’ve left out the membrane. Verify locally, but treat that 55-60% as your anchor.

Where the Quiet Omissions Hide The sneakiest costs are the ones that look like they’re included but aren’t. I’m talking about the builder’s allowance for “preliminaries”—site toilets, temporary power, skips, and the project manager’s time. I’ve seen quotes where prelims are 5% and others where they’re 15% for the same job. Also, check the groundworks line. Is it fixed or “on survey”? If it’s the latter, you’re signing a blank cheque for whatever clay, roots, or old septic tank they dig up. And always ask for the drainage layout to be itemised—not lumped into “external works.” That lump hides a thousand pounds.

Comparing Quotes Like a Human, Not a Spreadsheet Don’t compare the total. Compare the *specification* line by line. One builder might quote “standard white sockets”; another might quote “brushed steel.” Same house, £3k difference. I make my clients list the top twenty components—windows, doors, insulation, kitchen units, bathroom sanitaryware, roof tiles—and force each builder to put their exact product and model against each. Then you’ll see the real gap. Also, ask each one what their *exclusions* are. The honest ones will list ten things. The cowboys will list two. That’s your red flag.

The Geometry of Your Own Plot (Don’t Fight It) While you’re budgeting, remember the shell cost is partly dictated by your site’s shape. Typical setbacks are around 3 metres from side and rear boundaries, and 5 metres from the street—but that’s guidance, not gospel. Fire gaps between buildings can be 6 to 15 metres depending on wall material. Verify with a local professional before you design that dream window. I’ve seen a beautiful plan die because the side passage was 0.9 metres instead of the 1.2 needed for a fire-rated wall. Also, watch the kitchen work triangle—keep the hob, sink, and fridge between 1.2 and 2.7 metres apart. And if someone suggests a double-height void, ask them where the upstairs floor went. That void eats usable square footage and your heating bill.

The Real Cost of “Cheap” I’ll leave you with this: the shell is the part of the house you can’t see when it’s finished, but it’s the only part that holds you up. If you’re tempted to shave 5% off the shell to afford better taps, don’t. You’ll feel that draft for thirty years. Spend the money on the structure, the insulation, and the waterproofing. The rest is furniture with a power supply.

What’s the most shocking omission you’ve spotted in a builder’s quote—or the one you nearly signed?

(Norms and setbacks vary by country — treat specific figures here as guidance and verify with a local professional.)