Nobody starts a renovation expecting to go over budget. And yet, almost everyone does. Not because they were reckless, or didn't plan, but because there are costs that simply don't show up until the work has already started, and by then it's too late to do much about them.
Keen to understand exactly where renovation budgets unravel, I called two people who'd been through it firsthand: Sarah James, who project-managed a full home renovation, and Katie Treadwell-Haas, who has been renovating her 1950s house room by room for the past two years. Between them, they had six things to say that every renovator needs to hear before they start...
1. Your builder's spec isn't always your spec
There's a version of budgeting where you get a quote, nod along, and assume that what you've asked for is what you'll get. But that isn't always the case, and the gap between those two things is where a surprising amount of your renovation costs can spiral.
Article continues below"Generally a builder will price for the cheapest they can get away with," explains Sarah James, having just finished renovating her family home. "Unless you specify the exact spec and type you want, that's what you'll get. This is something you should consider carefully before getting your quote, and discuss with your builder what quality level they are going for."
In her case, that gap showed up first in the details – architraves and skirting boards that were functional but not quite what she'd envisioned. Then came the doors. The architect had drawn standard-width openings, the most budget-friendly option, and the builder priced accordingly. It was only when Sarah started looking at doors properly that she realised wider ones existed and that they would have suited the house far better, particularly downstairs. But by that point, the gaps had already been built.
"It honestly would have looked better if we'd had wider doors," she reflects. "You just don't know what you don't know – which is why it's so important to explore every option at the planning stage, before anything gets built."
The Takeaway: Before agreeing any quote, sit down with your builder and go through every line. Ask what brand, grade and finish they've priced for, and use the planning stage to explore all your options, not just the ones your architect has drawn up. The cheapest option on the plans isn't always the right one for your home.
2. Expect the unexpected and budget for it
While every renovator has a priority list at the start of a project, what nobody tells you is how quickly an unexpected problem can tear it up and hand you a completely different one.
Katie Treadwell-Haas discovered this firsthand when unexpected draughts from ageing windows forced her to rethink her entire renovation timeline. "Once we realised the windows were an issue, we had to rethink the sequencing of all the work," she explains. "My number one priority had been the kitchen remodel, but the windows jumped straight to the top of the list."
She got three quotes and the spread was eye-opening. The cheapest came in around £3,000 lower than the others but would have required Katie to obtain the relevant FENSA certification herself. "We ended up going with the more expensive option because I just wasn't convinced the quality would be there otherwise," she says. "If something needs to be done properly, get it done properly."
The Takeaway: Build a contingency into your budget that is ring-fenced for unexpected discoveries (not just upgrades). Before committing to any sequence of work, you should also get the condition of your property properly assessed so that surprises surface on your terms, not the builder's.
3. Check for hidden regulatory and structural costs before you start
Of all the unexpected renovation costs, the ones that arrive via a letter from the planning authority are arguably the most dispiriting.
"Initially, there was no discussion about a requirement for a bat survey," sighs Sarah. "If you live in our area, a bat survey is required if any part of the roof is disturbed. We were not informed of this by our architect, and the planning authority did not mention this until our planning had been in place for at least 12 weeks." What followed was a cascade of surveys, each triggered by the last – all because there was apparently one piece of bat poo in the loft. The surveys can only be carried out at specific times of year, and missing the window means waiting out an entire build season.
Asbestos is another cost that has a habit of announcing itself at the worst possible moment, and Katie Treadwell-Haas says it's something every renovator should factor in from the outset. Samples may need to be sent away for testing, and removal, if asbestos is found, can be significant. She discovered this firsthand when she had a asbestos survey carried out as part of her buying process.
"There is some in the house," she says matter-of-factly – a chrysotile tile beneath the stairs, left undisturbed beneath what she suspects is an original 1950s carpet. "It's not a problem as long as you don't disturb it, but at some point when we improve the under-stairs storage we'll have to get a professional to bag and remove it properly." She also had an asbestos downpipe, and her home's no-fines concrete construction brought its own structural considerations, including the need to angle-grind off old guttering before new PVC could go in. "Which is a great way to spend over five grand," she laughs.
The Takeaway: Older properties in particular carry hidden compliance and structural costs that no quote will include unless you've specifically investigated them first. A good architect should flag these risks early. If yours hasn't, ask directly. Missing a survey window can delay your entire project by a year.
4. Never underestimate the cost of the garden
"Do not underestimate how much extra you can spend on the garden to make it look as good as your house," says Sarah James, herself a garden designer. "You don't want a finished house and an unfinished area around it. Factor this in right from the beginning. The cost is the same as inside, and whilst we did budget for this, it is very expensive nonetheless."
The other mistake, she says, is assuming your builder is the right person for the job. "It is advisable to use a landscaper rather than your builder for the garden. This is often done at the end of the build, and the builder is in a rush to get onto the next job and won't spend the time required to make your garden look good. A landscaper understands drainage, the right soil for flowerbeds, and how weather impacts every aspect of the build." When it comes to the handover between the two, Sarah is unequivocal: "Discuss where the builder finishes and where the landscaper starts. These are important points – who is responsible for what – and get the pricing right."
The Takeaway: Budget for the garden at the very start of your renovation, not as an afterthought at the end. Use a landscaper rather than your builder for outside work, and agree in writing exactly where one's responsibility ends and the other's begins.
5. Write a Schedule of Works and make it obsessively detailed
If there's one document that separates renovations that stay on budget from ones that don't, it's the Schedule of Works.
"The most important thing we did to help keep us on track with the budget was to compose a very comprehensive Schedule of Works," says Sarah. "This was broken down into many sections and subsections so that the builder could put a price under each one. We knew we needed 15 doors, so they priced for 15 doors, the fitting of 15 doors, painting, hinges and door furniture. We gave the square meterage of all the tiling and how much we were prepared to spend per metre. All electrical work was included too – we had a very specific electrical plan drawn up so they could price off it precisely."
The value of that document revealed itself almost immediately. "They tried to charge us more for the electrical works, which is quite common," says Sarah. "We were able to refer back to the Schedule and discuss why the price had changed. It took us weeks and weeks to complete, but it was worth every hour."
The Takeaway: Write a Schedule of Works before you agree any quote and make it as detailed as you possibly can. You can use this as a reference point throughout the build, and refer back to it the moment any costs start to creep.
6. Know who is managing your build and what that actually means
There's a question that almost every renovator forgets to ask until it's too late, and it's this: who is managing your build?
"The builder will probably say they will manage it," says Sarah, "but find out exactly what this means. Do they manage every aspect of the build – all the workmen coming into the property, organising them all to arrive when required? Managing a build requires a huge amount of organisation. You can also get a professional property manager in to manage the build for you, but still be prepared for many questions to come your way."
It's worth being honest with yourself about how much time and headspace you have to field those questions, because they will come regardless of who is nominally in charge. The more complex the build, the more you need someone whose sole job is to keep all the moving parts moving.
The Takeaway: Before work starts, establish clearly who is managing the project day to day, what that actually involves, and whether you need a professional project manager to take it on.
What no one tells you about renovating is that the costs that hurt most aren't necessarily the big structural surprises. Often it's the small decisions made too early, or not made at all. From the finishing details that make your renovation look cheap to the survey results that raise red flags, the best defence is always the same: ask more questions before you start.
