Variations and Extra Costs on Building Work
Changes are a normal part of building work. What keeps them from becoming disputes is agreeing each one, and its price, before the work is done.
The short version
Changes are a normal part of building work. Agree each one, and its price, before it is carried out.
A variation is any change to the work you agreed when you accepted the quote: something added, something removed, a different material or a different way of doing it. Some variations come from you. Others come from what the contractor discovers once the job is under way.
Variations are the usual reason a building job ends up costing more than the quote. That isn't a sign that anything has gone wrong. It becomes a problem only when changes are made without a clear agreement on what they are and what they cost, and the first time the homeowner hears the price is on the final invoice.
This guide covers where extra costs come from, who usually pays for what, and a simple way to agree changes so the final bill holds no surprises. It is part of our homeowner's guide to building quotes and payments.
The definition
What counts as a variation
Your accepted quote describes a piece of work at a price. Anything that changes that description is a variation. It might add to the work, reduce it or change how it is done. It might increase the price, reduce it or, occasionally, leave it the same.
It helps to separate variations from two things that look similar. The first is a provisional sum being settled. If your quote included an allowance for work that couldn't be priced in advance, adjusting it to the real cost is not a change to the job; it was always part of it. Our guide to provisional sums explains how those work.
The second is putting right the contractor's own work. If something has to be redone because it wasn't done properly the first time, that is not a variation, and it isn't normally something you pay extra for.
Keeping these apart makes conversations about cost much simpler. When an extra is proposed, the first question is always: is this a change to the job, an allowance being settled, or something that should have been in the price already?
Where extras come from
Six common sources of extra cost
Most extra costs on a domestic job come from one of these.
You change your mind
A different finish, a different layout, a different product. Changing a decision after work is planned or ordered usually costs something, even if the new choice costs the same.
You add something
While the scaffold is up or the room is open, it is tempting to add a job. It can be good value, but it is new work and it will be priced as such.
Something is uncovered
Opening up an existing building can reveal things nobody could have seen. Whether that is an extra depends on what the quote said about it.
An exclusion comes into play
If the quote excluded something that turns out to be needed, it will be priced separately. Reading the exclusions before you accept tells you where this could happen.
An allowance is exceeded
A provisional sum that comes in above its allowance increases the total. Strictly it isn't a variation, but it shows up on the final bill in the same way.
A product becomes unavailable
If the specified material can't be obtained, a substitute may cost more or less. Any substitution should be agreed with you before it is made.
Agreeing a change
How to agree a variation properly
It takes a few minutes and a short email. It saves far longer later.
Describe the change
Whoever raises it, get a clear description of what will be done differently. "Replace the rotten section of timber" is better than "sort the timber out".
Get the price
Either a fixed price for the change, or an agreed rate and a sensible estimate. Ask whether it includes VAT.
Ask about the knock-on effects
Does the change affect the timing of the job, other parts of the work or the warranty? Better to know now.
Confirm it in writing
An email or message setting out the change, the price and any effect on timing is enough. Reply to confirm you agree. Keep it.
Then the work goes ahead
The order matters. Agreeing the price before the work is done is what keeps the final bill predictable.
Keep a running total
Add each agreed change to a simple list alongside the original price. At the end of the job, you'll know what the final figure should be before the invoice arrives.
Who pays
Who usually pays for what
The answer depends on what your quote and contract say. These are general patterns, not rules.
Usually the homeowner's cost
- Changes you ask for
- Additions to the agreed work
- Upgrades to a better material or finish
- Work the quote clearly excluded
- Provisional sums settled above the allowance
- Genuinely unforeseeable work the quote allowed for
Worth questioning
- Work that was part of the described scope
- Extras presented only after the work was done
- Putting right the contractor's own mistakes
- Costs caused by the contractor's own delays
- Items a competent quote would normally include
- Substitutions made without asking you
Under the Consumer Rights Act 2015, a trader providing a service to a consumer must carry it out with reasonable care and skill, and where no price has been agreed, the consumer must pay a reasonable price. Agreeing each change and its price in advance avoids relying on what counts as reasonable. Citizens Advice explains your rights in more detail. This is general information, not legal advice.
Staying in control
How to keep extra costs down
Decide as much as you can before the quote. The more settled the design, materials and finishes are when the contractor prices the work, the fewer changes there are later. Our guide to what a building quote should include sets out what to look for.
Ask about the unknowns at the site visit. A good contractor can usually tell you what might be found once work starts, and roughly what it would cost. You can then budget for it rather than be surprised by it.
Read the exclusions. Anything the quote excludes is a potential extra. Ask whether each exclusion is likely to be needed on your job.
Keep some money in reserve. It is easier to hold back part of your budget for the unexpected than to hope nothing comes up. How much depends on the job and how much of it is uncertain.
Ask for options when a change is recommended. If the contractor suggests extra work, ask why it is needed, what happens if it isn't done now, and whether there is more than one way to do it. Sometimes there is a cheaper option that is perfectly sound. Sometimes the recommended fix is the only sensible one, and knowing why makes the decision easier.
Limit changes once work starts. Every mid-job change has a cost beyond the change itself: reordering, rescheduling and disruption. If you do want to add something, raise it early rather than when that part of the job is nearly done.
Get everything in writing. A clear written contract, and written confirmation of every change, is the foundation. Our answer on whether you need a written contract for building work explains why.
When an extra is a surprise
What to do if an unexpected extra appears
Sometimes an extra charge appears that you weren't expecting, often on the final invoice. The calm approach usually resolves it.
Start by asking for a breakdown: what the charge is for, when the work was done and how the figure was calculated. Then compare it with your quote. Was the work already described in the scope? Was it excluded? Was it a provisional sum being settled? Did you ask for it, even informally?
If you did ask for the work, it is fair to pay for it at a reasonable price, even if the price wasn't agreed at the time. If the work was already in the scope, it should already be in the price. If neither of you raised it and it simply appeared, it is reasonable to ask why you weren't told before it was done.
Most of these conversations settle quickly when both sides look at the same documents. If the extra comes from a price rise rather than a change to the work, our answer on what happens if the price goes up covers that situation. Our answers on whether a builder can change the price after quoting and who pays for extra work cover the common cases. If you are still unhappy at the end of the job, our answer on what to do if you are not happy at the end of the job sets out the next steps.
At the end of the job
Checking the final account
The final invoice should reflect three things: the original quoted price, every agreed variation and every settled allowance. If you kept a running total, checking it takes minutes.
Ask for the invoice to list each variation separately rather than bundling them into one figure. It makes it easy to match each one to what you agreed, and it gives you a clear record for later. Our guide to invoices and receipts explains what to keep.
If there are small items still to finish or put right, raise them before you make the final payment. Our guide to final payment and snagging covers how to handle that fairly.
How Mortaro helps
Questions answered while the work is under way
Mortaro coordinates domestic building work, carried out by an independent main contractor from our network. Your construction contract is with your contractor, who is named in your written quotation, so that quotation is the clear reference point for what was agreed.
While the work is going on, you talk to us. If something comes up, or you want to ask about a change, we put it to your contractor and get the answer back to you, including at the times they are working and unable to respond. A question about extra work shouldn't have to wait until the contractor is off site.
Who you're dealing with explains how the three parties fit together.
Straight answers
Questions about variations and extras
Can a builder charge for extra work I didn't agree to?
It depends on the circumstances and on what your contract says. If you asked for the work, a reasonable price is generally payable. If the work wasn't requested or discussed, it is fair to ask why you weren't told first. Agreeing every change in writing avoids the question.
Does a variation need to be in writing?
It is strongly advisable. A short email setting out the change and its price, which you reply to and confirm, is usually enough and gives both sides a clear record.
What if I want to remove something from the job?
That is a variation too, and it should reduce the price. Agree the reduction in writing. If materials for that part have already been ordered, some of the cost may still be payable.
How much should I keep aside for extras?
There is no set figure. It depends on how much of the job is uncertain, especially on older properties where work involves opening up existing structure. Ask the contractor at the site visit what could come up, and plan around their answer.
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