How to compare builders' quotes like-for-like

Getting three quotes for an extension or loft conversion is sensible, but the numbers at the bottom are rarely comparable as they stand. One builder has included things another has left out; one has priced your kitchen and another has not; one quote includes VAT and another does not. This guide explains how to read a builder's quote, what to look for, and how to put quotes side by side so you are choosing between like and like.

Give every builder the same information

The single most effective way to get comparable quotes is to give every builder the same brief. Ideally that means a full set of drawings, the structural engineer's calculations and a written specification describing the finishes you want. Without them, each builder has to make their own assumptions about everything from the depth of the foundations to the type of roof lights, and their prices will reflect different jobs.

If you do not have a detailed specification yet, ask each builder to list their assumptions in writing. That list is often as useful as the price itself.

Quote or estimate?

A quote should be a fixed price for a clearly defined scope of work: if the job does not change, the price should not either. An estimate is a builder's best guess, which can go up as the work progresses. Some documents mix the two, with most items fixed and others estimated. Check which you have, and ask for anything described as an estimate to be firmed up or explained.

Provisional sums and prime cost sums

Quotes for building work often include provisional sums and prime cost (PC) sums. A provisional sum is an allowance for work that cannot yet be priced accurately, for example repairs to a structure nobody has opened up yet. A prime cost sum is an allowance for items you have not chosen yet, such as tiles, sanitaryware or a kitchen, where the final cost depends on your choice.

These allowances are normal and useful, but they are also the easiest place for quotes to look cheaper than they are. A low PC sum for bathroom fittings, for example, may not buy what you have in mind. When comparing quotes, line the allowances up against each other, and consider replacing them with the same figure in each quote so you are comparing the builders' own work rather than their guesses about your taste.

Exclusions and who pays for what

Read the exclusions as carefully as the inclusions. Items that are often excluded, or priced separately, include: planning and building control fees, party wall surveyors' fees, the structural engineer, skip and scaffold licences, removal of asbestos or other hazards found during the work, the supply of the kitchen or bathroom fittings, decoration, flooring, and external works such as landscaping. None of these is wrong to exclude, but a quote that includes them will naturally be higher than one that does not.

Preliminaries are another area to compare. They cover the costs of running the site: scaffolding, skips, welfare facilities, temporary protection, insurance and supervision. Some builders show them as a separate line, others spread them through the price.

VAT

Check whether each quote includes VAT. A VAT-registered builder must charge it on most domestic building work, and some quotes show prices before VAT. A builder who is not VAT-registered will not add it, but on a large project that can also be a sign of a very small business, so it is worth understanding how they are set up.

Programme and payment schedule

A good quote comes with an indication of how long the work will take and how payments are staged. Stage payments linked to progress, such as foundations complete, weathertight or first fix complete, protect both sides, because you are paying for work that has been done. Be cautious about paying a large sum upfront, except for items that genuinely have to be ordered and paid for in advance, such as bespoke windows.

The contract and changes

For anything larger than a small job, use a written contract. Standard forms written for homeowners, such as the JCT contracts for home owners and occupiers, set out the price, the scope, the programme, how payments are made and how disputes are handled. The contract should also say how variations, changes you or the builder want to make once work starts, are agreed and priced, ideally in writing before the extra work is done.

Under the Consumer Rights Act 2015, a builder must carry out work with reasonable care and skill. If you sign a contract at home rather than at the builder's premises, you will usually have a 14-day cancellation period. Both apply whatever the paperwork says.

Checking the builder, not just the price

A quote is only as good as the company behind it. Check that a limited company is registered at Companies House and has been trading for a reasonable time: our own record, company number 08057223, shows we have been registered since 2012. Ask to see the builder's public liability insurance, and ask for references from recent similar projects, ideally in your area, which you can phone or even visit. Read their reviews on independent sites.

Think about who will actually run your job. A company where the director leads each project personally, as ours does, works very differently from one where a salesperson hands you on to a site manager you have never met.

Red flags

Be wary of a price far below the others without a clear reason; it usually means something has been left out or will be charged later. Other warning signs include no written quote, a request for cash only, pressure to sign immediately, a large upfront payment, a builder who cannot show insurance or past work, and a reluctance to put changes in writing. A slightly higher quote from a builder who explains everything clearly is often the cheaper choice by the end of the job.

Putting quotes side by side

Once you have the quotes, list the main parts of the job down one side of a page, with a column for each builder: groundworks, structure, roof, windows and doors, services, finishes, preliminaries, allowances, exclusions and VAT. Fill in what each has included, and the gaps become obvious. From Wimbledon to Richmond, our area pages explain the local planning context your builder should be allowing for, including in Richmond, where every basement needs planning permission. Our house extensions page explains how we price and run a project, and we are always happy to talk you through our quote line by line.