What is extra work, and how do I avoid bills I didn't plan for?
Extra work is everything that wasn't in the quote. It happens either because the quantities were wrong, or because something unexpected turned up. You can remove the first kind entirely by measuring properly; the second you can only agree your way around in advance.
Short answer: extra work (sometimes called variations) is work beyond what the quote covers. It has two sources: quantity errors (the room was bigger than anyone thought) and unforeseen conditions (rot, damp, old wiring or pipework behind a wall). Quantity errors you remove by supplying measured figures from the start. Unforeseen conditions you cannot remove — but you can agree in writing that you must be contacted and must approve before work continues. Put a figure on that threshold.
The two kinds of extra work — and they need different handling
All extra work falls into one of two boxes, and the difference decides what you can do about it.
Quantity extras arise when something everyone knew had to be done turns out to be more than anyone allowed for. The living room was 33.8 m² of net wall, not 30. There were 18 running metres of skirting, not 14. There were seven windows, not five. This kind is not unpredictable — it is simply unmeasured. It can be removed entirely.
Condition extras arise when something hidden turns up: damp in an outer wall, a subfloor that will not hold, three layers of wallpaper under the felt, an old pipe behind the plasterboard. Neither you nor the contractor can see this in advance without opening something up. This kind cannot be removed — only agreed for in advance.
The most common mistake is treating quantity extras as if they were condition extras: accepting "well, the room was bigger than we thought" as if it were an act of nature. It wasn't. It was a figure nobody had measured.
How to remove quantity extras
Give the contractor the quantities before a price is set:
- Net wall area per room — the wall area minus doors and windows.
- Floor and ceiling area in internal measurements, not the official floor area of the home — that is measured outside the outer walls and is therefore larger than the actual floor inside the rooms.
- Ceiling height, measured at three points — lowest and highest, not an average.
- Number and size of every door and window, with location.
- Running metres of skirting after deducting doorways.
Once the quantities are in the quote, they are part of the agreement. If it turns out there was 10% more wall than stated, that is still a discussion — but now it is a discussion about a deviation from an agreed figure, rather than about what someone had imagined.
So ask that the quote states the quantities it was priced on. A quote that just says "paint the living room" cannot be checked. A quote that says "painting 33.8 m² of net wall in two coats" can.
How to tame condition extras
You cannot predict them. You can control what happens once they turn up. Four sentences do most of the work, and they need to be in the written agreement:
- "Extra work only starts once I have approved it in writing." Without that sentence, a phone call on site can turn straight into a line on the invoice.
- "Extra work is charged at the agreed hourly rate plus documented materials." Write the hourly rate into the agreement while you are still on good terms about it.
- "I must be contacted before the total price exceeds an agreed ceiling." A specific figure in the agreement beats "if it gets a lot more expensive".
- "Extra work is described with quantity and price before it is carried out." That way it is a small quote, not a surprise.
For larger jobs, most places have a standard set of building contract terms for work between a private client and a contractor, which among other things sets out how extra work should be ordered and charged. Such terms rarely apply automatically — they have to be agreed in writing. If you are unsure what applies in your situation, ask a professional; an article is not legal advice.
What you can do yourself to cut down the unknown
Some hidden conditions can be uncovered before work starts — and it is far cheaper to know about them at the planning stage than to discover them on day three:
- Cut a hole. A 20 × 20 cm test opening in a plasterboard wall costs almost nothing to patch up again and can settle what is inside.
- Lift a floorboard in a corner and look at the subfloor.
- Dig up old drawings from the public building case archive. They are not always accurate, but they show what was intended.
- Ask for a building condition survey on larger projects — especially in a home that has been standing for several decades.
- Photograph everything before work starts. It settles a surprising number of disagreements afterwards.
The contingency: plan for it, and don't spend it
A common approach on renovation jobs is to set aside a contingency on top of the agreed price. The size depends entirely on how much is hidden: in a fully renovated flat with a known substrate the need is small, while a house from the 1930s with work touching the structure and the services can call for considerably more. Agree the size of the contingency with the contractor based on the reservations the quote contains — those are what show where the uncertainty actually lies.
The point of a contingency is not to have more money to spend. It is to be able to say yes to a necessary piece of extra work without having to cut another room out of the project halfway through.
The one thing that must never be left as "we'll see what happens"
Whether a wall is load-bearing. If a wall is to be removed or broken through, neither a tape measure, a LiDAR scan nor an app can decide that — a scan measures a wall's thickness and position, not what rests on it. That calls for a building surveyor or a structural engineer — and the work also needs approval from the authorities before it starts.
It is also the most expensive thing to discover partway through: a load-bearing wall typically needs a calculated beam, support, and an approved solution. Get it settled before quotes are gathered — otherwise it is not extra work, it is a new project.
How to get the quantities right from the start
You can measure by hand with a tape measure; allow 10-20 minutes per room once the ceiling height needs measuring at three points and every opening needs four figures.
HouseSense builds the quantity basis for you. Whether you scan the home with LiDAR on an iPhone Pro — or draw it yourself on screen from your own measurements — the app's takeoff works out net wall areas with doors and windows deducted, totals the floor and ceiling areas and ceiling heights, and lists every opening in a window-and-door schedule. That becomes a PDF you can attach to the quote request, so the quantities are an agreed part of the basis rather than a guess.
The app cannot see inside a wall — and should not pretend to. But it can make sure that the half of extra work that should never have happened in the first place, doesn't.