How to compare builders' quotes like for like

A builder's quote only means something next to another builder's quote once both are describing the same job. Most of the time they aren't, and the totals at the bottom are the least useful numbers on the page.

Here is how I'd compare them if I were the one paying.

Make everyone price the same thing

The biggest cause of quotes that can't be compared is a loose brief. If three builders price from a sketch, each one fills the gaps differently. One assumes a mid-range kitchen, one assumes you're buying it yourself, and one hasn't thought about it at all.

Before you ask for prices, have:

• Drawings that are as complete as you can get them, ideally building regulations drawings rather than planning drawings
• A structural design, so everyone prices the same steel and the same foundations
• A schedule of works listing what is to be done room by room, including the dull items like making good, decorating and what happens to the garden
• Your main finishes, or at least a stated allowance for each one

Then ask every builder to price against the same schedule, line by line if possible. A builder who won't break a price down is making your job harder.

Read the exclusions before the total

Every quote leaves things out. Some say so clearly. Some just don't mention them. Typical gaps include:

• Kitchen, flooring or sanitaryware supply
• Decoration
• Electrical work beyond the new space
• Making good and landscaping outside
• Building control, party wall and water company fees
• Asbestos removal, if any is found
• Skips, scaffolding or a temporary kitchen

List what each quote excludes, put a realistic figure against each gap, and add it back on. The order often changes.

The cheapest quote is often just the one that has left the most out.

Preliminaries, allowances and VAT

Preliminaries are the costs of running the site rather than building anything: supervision, scaffolding, welfare, skips, insurances, protection and setting up. Some builders itemise them. Others spread them across their rates. Very low prelims can mean less supervision, or a programme that assumes everything goes perfectly.

Provisional and PC sums are allowances for things not yet known or chosen, and they need levelling across quotes before any comparison is fair. I've covered how in provisional sums and PC sums.

VAT is easy to get wrong. Building work to an existing house, including an extension, is normally charged at the standard 20 per cent. Check whether each quote includes it. A builder who isn't VAT registered won't charge it, so make sure you are comparing like with like. New homes are treated differently, and your accountant can tell you how the rules apply to your project.

Programme, payments and the contract

Programme. Ask each builder for a written programme with the main stages. A builder promising a much shorter programme than everyone else should be able to explain how.

Payments. Payment should follow the work, in clearly defined stages you can see on site. A large payment up front, other than for specific items with long lead times, is a warning sign.

The final payment. Check what is held back until the snags are done, and on what terms. There is more on that in snagging an extension.

Variations. Ask how changes are priced and agreed. Every change should be priced in writing before it is carried out.

The contract. There should be a written contract, not a quote and a handshake.

Laying it out, and a second opinion

A simple spreadsheet does the job. Your schedule of works down the side, one column per builder. Add rows for the exclusions you've priced, the levelled allowances, the prelims and the VAT. Then look at the totals again.

After that comes the part a spreadsheet can't do: who will actually run the job, what they have built before, and whether you can go and see it. Those questions are in eight questions to ask a builder before you sign.

Our working rates are on the cost guide, so you can sense-check any quote against them. If you send us the drawings and your schedule, you'll get a price you can lay alongside the others line by line, from the person who would run the job.