How to compare builders' quotes without getting caught out

You asked three builders for a price on the same extension. One came back at £48,000, one at £61,000, and one at £74,000. Everyone tells you to get three quotes and nobody tells you what to do when they look like this.

The instinct is to assume the cheap one is cutting corners and the expensive one is trying it on. Usually neither is true. Three honest builders pricing the same drawing will produce three different numbers, because they have made different assumptions about what the job includes — and unless you find those assumptions, you are not comparing prices at all.

The quotes are not for the same job

Start from the assumption that they are pricing different scopes, because they almost always are. The most common places the difference hides:

Groundwork and foundations. Nobody knows what is under your garden until somebody digs. One builder has priced a standard trench fill at an assumed depth; another has allowed for a metre deeper because there is a mature oak three gardens away. If the drawing does not specify a foundation design, that line is a guess, and the size of the guess varies enormously.

Drainage. Is there a manhole in the footprint? Moving one is a day and some concrete. Diverting a shared sewer needs an agreement with the water authority and can add weeks. If one quote is silent on drainage, it is not free — it is unpriced.

The finish. “Plastered and ready for decoration” and “decorated” are different jobs. So are “supply and fit sanitaryware” and “fit customer’s sanitaryware”. Kitchens are the worst offender: a £48,000 quote that excludes the kitchen units and a £61,000 quote that includes a £12,000 kitchen are the same price.

Structural steel. A steel beam has to be designed by an engineer, made, delivered, and lifted in. If one quote includes the engineer’s fee and the others assume you are providing calculations, that is over a thousand pounds of difference before the steel itself.

VAT. Some builders quote including, some excluding. On £60,000 that is a £12,000 discrepancy that has nothing to do with the building work. Check every time.

What a fair comparison actually needs

You cannot compare quotes properly unless all three were asked to price the same thing. That means giving every builder the same information, in writing, before they price:

• The drawings, if you have them, and the structural calculations if they exist
• Whether you are supplying anything yourself, and if so exactly what
• The specification for anything you care about — the floor finish, the windows, the type of roof covering
• Any date constraints, because working around them costs money
• Access: whether there is side access, whether a skip can go on the drive, whether a lorry can get down the road

If you leave those open, each builder fills the gaps with their own assumptions and you get three numbers that cannot be lined up.

Reading the quote you get back

Once the quotes come in, the useful test is not “which is cheapest” but “which one can I check”. A quotation you can interrogate is worth more than a lower one you cannot.

Look for these:

Is it itemised? A single figure with the word “extension” next to it tells you nothing and gives you no way to discuss a change later. If you decide mid-build that you want a bigger opening, an itemised quote lets you both see what that moves. A lump sum turns every change into a negotiation from zero.

Are exclusions written down? Good quotes say what they do not cover. “Excludes: kitchen units and appliances, floor coverings, decoration, planning fees” is a builder being straight with you. No exclusions list usually means the exclusions exist but have not been said out loud.

Are provisional sums flagged? Some things genuinely cannot be priced until the work opens up — the state of a roof structure, what is behind the render. A provisional sum is an honest placeholder. What matters is that it is labelled as one, and that you know how it will be settled when the real number appears.

Is there a payment schedule? Payments should follow completed work — after the slab, after the roof is on, after first fix — not a calendar. A large deposit before anything happens is worth asking about.

The question that sorts it out

When the quotes are back and they still do not line up, go back to each builder with the same question:

“Quote B has priced X and yours does not mention it. Is that excluded, or included somewhere I have not spotted?”

The answer tells you two things. It tells you what the real difference is, and it tells you how the builder behaves when they are questioned. You are going to be asking that person awkward questions for three months. Finding out now how they handle one is worth more than the price difference.

Cheapest is not the risk people think it is

The genuine risk in the cheap quote is not that the builder is dishonest. It is that they have under-priced by accident, discovered it in week four, and now have to find the money somewhere — by rushing, by pushing variations, or by moving to a job that pays better and leaving yours half done. That is a much more common failure than deliberate corner-cutting, and an itemised quote makes it visible early.

If a price is well below the others and you cannot find the reason in the scope, ask directly what they have assumed. A builder who has genuinely found an efficiency will be pleased to explain it.

What to do next

Get everything on the same footing before you compare anything: same drawings, same specification, same list of what you are supplying. Then ask each builder for an itemised quotation with exclusions written down.

If you are at that stage and want a price you can actually take apart line by line, tell us about the project — an itemised written quotation is how we quote everything.