A working budget needs three layers — the build cost, the fees and consents around it, and a contingency sized to the actual risk of the property, not a round number picked because it sounded sensible.
This is written from the position of someone pricing older Kent housing stock daily: oast conversions, Wealden farmhouses, Victorian terraces and 1930s semis. What follows is how to set a figure you can actually hold to.
Start with scope, not a number
Budgets that start as 'I've got £60,000 to spend' rather than 'this is what I want built' tend to produce disappointment, because the number was fixed before anyone worked out what it needs to cover.
Better to define the brief first — rooms, finishes, structural changes — get it costed properly, then decide what to trim if the figure is higher than hoped. Trimming a defined scope is straightforward; stretching a fixed number to cover an undefined one is not.
What the headline figure needs to include
The build price is only part of the total. Design and structural engineer fees, planning and building control fees, party wall costs where relevant, VAT, and often a period of alternative accommodation or storage all sit outside the contractor's quote.
Furniture, curtains, appliances and landscaping are routinely forgotten and can add a meaningful percentage to a project that otherwise looked fully costed.
- Design and structural engineer fees
- Planning, building control and party wall fees
- VAT (usually at the standard rate — see our VAT guide)
- Alternative accommodation or storage if the house is unliveable
- Furniture, white goods, curtains and landscaping
Sizing contingency to the actual risk
Contingency is not a nice-to-have on top of the budget — it is part of it. The right size depends on how much of the property is hidden from a survey: a straightforward single-storey rear extension on a modern house carries less risk than opening up a 300-year-old timber frame.
As a general steer, newer, well-documented properties can budget contingency at the lower end of what most professionals recommend, while period or previously altered properties, or anything involving structural work below ground or within existing walls, should sit at the higher end. We'll flag which category your project falls into at the site visit rather than quoting a single figure for every job.
What actually eats into contingency on real jobs
In our experience the contingency spend is rarely one dramatic discovery — it's a series of smaller ones. Rotten joists under a removed hearth, an unrecorded drain run, asbestos in an old boiler flue, brickwork that needs more rebuilding than expected once render comes off.
Decision changes mid-project are the other big drain, and they're avoidable: a kitchen layout changed after first fix, a window size altered after the opening is formed. These are client-driven variations rather than site discoveries, and they come out of contingency just the same.
Keeping the budget honest as the job runs
Ask for a running account of what's been spent against contingency, not just a final reconciliation. A good contractor will tell you as soon as something is found, price it before proceeding, and let you decide rather than surprising you at the end.
If contingency is being used up faster than the job is progressing, that's the signal to review remaining scope — better to cut a finish spec early than run out of money at second fix.
Phasing work if the whole scope doesn't fit the budget
Where the full wish list exceeds what's sensible to spend now, phasing structural and 'hidden' work first — foundations, drainage, first fix — and finishes later is usually better than compromising on the parts that are expensive to redo.
It's far cheaper to leave a room undecorated for a year than to open up a finished floor because the drainage wasn't extended while it was accessible.
Common questions
How much contingency should I really hold back?
It depends on the age and history of the property and how much structural work is hidden until it's opened up. Newer, well-documented houses can sit lower; period buildings, previous unrecorded alterations, or below-ground work justify a higher figure. We'll advise a realistic percentage at the site visit based on what we can see and what the drawings suggest is behind it.
Should contingency be spent on upgrades if nothing goes wrong?
No. If it isn't needed for unforeseen work, it's better returned to you or held for the final snagging period than spent on upgrades that weren't part of the original brief — otherwise you have no buffer if something does turn up late.
What's the biggest budgeting mistake homeowners make?
Fixing the total spend before the scope is defined, then trying to negotiate the design down to fit rather than the other way round. It's far easier to trim a properly costed scope than to guess how much of an undefined one a number will cover.
Does a fixed-price quote remove the need for contingency?
No. A fixed-price quote fixes the price for the scope that's been surveyed and specified. It doesn't cover genuinely unforeseeable conditions found once walls, floors or ground are opened up — that's what contingency is for, and a clear written quote will say what is and isn't included.
Can you help me set a realistic budget before I commit to a design?
Yes — our free site visit is exactly for this. We'll look at the property, discuss what you want, and give you an honest sense of the cost drivers and likely contingency before you spend money on detailed drawings.