How to compare builders' quotes beyond the headline price

Three quotes for the same extension can differ by £30,000, and the cheapest is often the most expensive by completion. The gap is rarely profit. It is scope, assumptions and provisional sums.

First, make the quotes comparable

You cannot compare prices for different jobs. Before you go out to tender, issue every contractor the same pack: the same drawings, the same written specification, the same schedule of finishes, the same start date and the same list of what you are supplying yourself. Ask for pricing in the same breakdown so lines can be compared side by side.

What to interrogate in each quote

• Provisional sums. A £6,000 provisional sum for a kitchen is a placeholder, not a price. Count how many there are — lots of them means the price is soft.
• Exclusions. Look for scaffolding, skips, welfare, temporary protection, making good, decoration, VAT and fees. These reappear later as extras.
• Prime cost sums for tiles, sanitaryware and ironmongery. Compare the allowance, not just the total.
• Preliminaries. Site set-up, management, insurance and plant. A price with no prelims line has hidden them, or forgotten them.
• Groundworks assumptions. Foundation depth is often assumed. Ask what depth is priced and what happens if it is deeper.
• Contingency. If the builder has not allowed any, you carry the risk.
• Payment terms. Monthly valuations against work completed are normal. A large deposit and front-loaded stage payments are a warning.
• Programme. A quoted duration that is half everyone else's is not efficiency.

Checks that are not about price

• Company registration, trading history and filed accounts.
• Public liability insurance (£5m is standard) and contract works insurance.
• VAT registration if the price is meaningful in size.
• Two references from projects of similar value and type, finished in the last two years — and visit one.
• A current site visit. Tidiness, protection and welfare tell you more than a brochure.
• Membership of a scheme such as FMB or TrustMark, and gas/electrical competent person registration where relevant.

The conversation that reveals the most

Ask each contractor: what worries you about this job? Confident builders will name the ground conditions, the access, the steel sequence or a detail the drawings have not resolved. A builder with no concerns has not read the drawings.

Use a proper contract

For domestic work, a JCT Home Owner Contract or JCT Minor Works contract sets out payment, variations, delays, defects liability and dispute resolution. An emailed quote is a weak contract. Agree a retention — typically 5%, half released at practical completion and half after the defects period — and a defects liability period of 6-12 months.

Red flags

• Pressure to decide this week to hold a slot.
• Cash discounts to avoid VAT — it puts your consumer protection at risk.
• No fixed address or no written specification.
• Unwillingness to work to your drawings, insisting on "we'll sort it on site".
• A price so far below the others that something has been left out. Ask what.

Next step

BuildWise Workspace sends one consistent enquiry pack to matched professionals near you and collects structured responses in a single place, so you compare like for like instead of reading three different documents.