How to Compare Builder Quotes Properly

You've done the sensible thing and got three quotes. They range from £85,000 to £140,000 for what's supposedly the same extension. Which one is right? Often, none of them — because they're not actually quoting for the same job.

Read the exclusions first

The cheapest quote is usually cheap because of what's missing, not because the builder is more efficient. Look for the exclusions list before you look at the total. Common items left out entirely: external drainage connections, structural steel supply (sometimes only the installation is priced), scaffolding, skip hire, building control fees, and making good to the rest of the house once the extension connects to it.

Provisional sums are a placeholder, not a price

"PS £2,000 for kitchen electrics" isn't a quote — it's a guess, and it's almost always a low one designed to make the headline number look better. Ask for every provisional sum to be justified, or better, replaced with a firm price once the scope is actually known.

Check the specification, not just the total

Two builders can both say "aluminium bifold doors" and mean very different things — a budget system versus a premium one can differ by thousands per opening. The same applies to insulation standards, flooring, and kitchen allowances. Ask for the actual product or an allowance figure per item, not just a category.

Where trade pricing changes the comparison

Materials are one of the biggest swing factors between quotes, and one of the easiest to get wrong when comparing on paper. A builder pricing a kitchen or bathroom "supply and fit" is usually including their own margin on top of retail — sometimes 15–20%. Where a project manager can source materials directly at trade prices instead, that markup disappears, and a quote that looked mid-table on paper can end up the cheapest in practice once it's compared fairly.

The real comparison

A proper like-for-like comparison means the same specification, the same exclusions made explicit, and the same contingency treatment across every quote. That's a few hours of careful reading — or it's the first thing I do when I review quotations for a client, before a single trade is appointed.