The Biggest Cost Surprises in Residential Refurbishments — and How to Avoid Them
Residential refurbishments have a habit of becoming more expensive than expected.
Sometimes that is because something genuinely unforeseeable is discovered once the building is opened up. But just as often, the problem is not the surprise itself. It is that nobody identified the risk, allowed for it, or agreed who would deal with it if it happened.
Here are some of the most common cost surprises we see on substantial residential refurbishment projects — and, more importantly, what you can do about them.
The quick answer
The biggest cost surprises on residential refurbishments usually come from:
Hidden conditions within the existing building.
Design changes and decisions made too late.
Provisional sums and allowances being mistaken for fixed prices.
Kitchens, bathrooms and other client-supplied items.
Existing mechanical and electrical services requiring more work than expected.
Access, logistics and other site constraints.
Small changes accumulating into a significant overall cost.
An inadequate — or badly managed — contingency.
You cannot eliminate every unknown from a refurbishment.
You can, however, identify where the uncertainty lies, put sensible allowances against it and manage it as the project progresses.
That distinction is important.
1. Hidden conditions: you don't know everything until you open the building up
This is probably the most obvious refurbishment risk.
A contractor removes a ceiling and discovers rotten joists. A wall is opened up and the construction is different from the drawings. Floorboards come up and reveal defective pipework. Existing drainage is not where anyone expected it to be.
Older buildings in particular can contain decades — sometimes centuries — of alterations.
The answer isn't simply to add an enormous contingency "just in case". A better approach is to identify the areas of uncertainty before tender and decide whether further investigation would be worthwhile.
That might include opening-up works, surveys or investigations before the main construction contract is placed.
Spending a relatively small amount obtaining better information before construction can sometimes remove a much larger financial risk later.
The important question
Rather than asking:
"What will this refurbishment cost?"
we also need to ask:
"Which parts of this cost do we know with confidence, and which parts are still uncertain?"
Those are two quite different questions.
2. Late decisions can be surprisingly expensive
One of the easiest ways to increase the cost of a project is to make important decisions after construction has started.
Changing a bathroom layout on a drawing is easy.
Changing it after the drainage has been installed is not.
The cost of a change can include much more than the new item itself. There may be abortive work, additional labour, alterations to other trades, programme implications and additional contractor management costs.
Sometimes the expensive part isn't actually what changed. It's when the change was made.
This is why important design decisions should be made as early as reasonably possible.
You don't necessarily need to select every door handle before the project starts, but decisions that affect structure, services, procurement or other trades need to be identified early.
The more developed and coordinated the design is before construction begins, the greater the opportunity to understand its cost before committing to the work.
3. A provisional sum isn't a fixed price
This is an area that regularly causes confusion.
A tender might contain an allowance of £10,000 for a particular element of work. It is easy to mentally treat that £10,000 as the cost.
But if it is a provisional sum, that may simply be an allowance because the work wasn't sufficiently defined when the contractor priced the project.
When the design is completed and the work is properly priced, £10,000 might become £8,000.
Or it might become £18,000.
That doesn't necessarily mean anybody has made a mistake. It means the cost was uncertain from the beginning.
A good cost report should therefore do more than provide a single headline number. It should help the client understand where the uncertainty sits within that number and how that uncertainty is changing as the project develops.
4. Kitchens and bathrooms: buying them yourself isn't quite as simple as it sounds
This deserves a section of its own because it is extremely common on residential projects.
A client may quite reasonably say:
"I'll buy the kitchen myself and the contractor can install it."
There is nothing inherently wrong with that arrangement.
It may give the client greater control over the specification and where they purchase it from. In some circumstances, it may also offer better value.
But it creates an important interface between the client, supplier and contractor.
Imagine a kitchen delivery arriving on site.
Who unloads it from the lorry?
Where is it stored?
Who checks that everything listed on the delivery note has actually arrived?
Who opens the boxes and checks the units aren't damaged?
What happens if a cabinet is scratched?
What if the supplier has sent the wrong worktop?
What if three small but essential fittings are missing and the joiner cannot complete the installation?
And who pays for the joiner to come back once the missing parts finally arrive?
Suddenly, "I'll supply the kitchen" is not simply a purchasing decision. It is a procurement and coordination decision.
The same applies to sanitaryware, tiles, light fittings, appliances, ironmongery and many other client-selected items.
Our rule of thumb
Every client-supplied item creates an interface that needs to be managed.
That doesn't mean clients shouldn't purchase items themselves. We regularly work on projects where that is entirely sensible.
It means the responsibilities need to be clear.
Before ordering, establish who is responsible for ordering, delivery dates, offloading, checking, storage, protection, installation and dealing with missing or damaged items.
The contractor may quite reasonably need to include costs for some of those activities even though they aren't supplying the product itself.
5. Existing services can create expensive surprises
Mechanical and electrical services are another common source of additional cost.
A refurbishment might initially appear to require relatively modest alterations to plumbing, heating, electrical or other services.
Then investigations reveal that the existing installation isn't suitable.
Perhaps the electrical distribution needs upgrading. The incoming supply is insufficient. Existing pipework needs replacing. Drainage needs altering. Or equipment that everyone assumed could remain turns out to be at the end of its useful life.
On substantial refurbishment projects, these discoveries can have implications beyond the individual item itself. They can affect ceilings, finishes, builders' work, plant space, programme and other trades.
Again, surveys and early investigation can help.
The important thing is not to assume that "existing" means "adequate".
6. Access and logistics can materially affect the cost
The cost of a major refurbishment isn't determined by the design and specification alone. The conditions in which the contractor has to deliver the work matter too.
Consider a substantial refurbishment where the contractor has good access, space for a site compound, straightforward deliveries, areas for material storage and room for skips and plant.
Now compare that with a major refurbishment of a city townhouse, listed building or constrained property where access is restricted, neighbouring properties are close by, storage is limited and deliveries have to be carefully planned.
The scope of work might be comparable, but the cost of delivering it can be very different.
Restrictions can affect scaffolding, temporary works, site establishment, deliveries, craneage and lifting, waste removal, material handling, protection, working hours and labour productivity. On a complex project, these costs can be significant.
They can also affect the programme. If materials cannot be stored on site, for example, deliveries may need to be phased around the construction sequence. If access is restricted, work that would otherwise be straightforward can require additional labour, plant or temporary works.
These costs are often captured within the contractor's preliminaries, and they are an important part of understanding why two apparently similar refurbishment projects can have very different overall costs.
The key is to recognise these constraints when establishing the budget and procurement strategy — not after the contractor arrives on site.
7. It's often the accumulation of small changes that causes the problem
Clients naturally focus on the big-ticket decisions.
But ten £1,000 changes have exactly the same effect on the budget as one £10,000 change.
A better floor finish here, additional sockets there, upgraded sanitaryware, different lighting, another fitted cupboard and a few additional external works can individually seem insignificant.
Collectively, they can become a substantial amount of money.
This is why good change control isn't simply about recording variations after they have happened.
Before committing to a change, you ideally want to understand its cost and any knock-on implications. Once agreed, it should be incorporated into the overall financial position so that everyone understands where the project is heading.
This leads to one of the most important principles of good cost management:
Forecast the final cost as you build.
If a £5,000 change is agreed today, the important thing isn't simply recording that £5,000.
It's understanding what that decision does to the expected final cost of the project.
8. Contingency isn't a pot of money that has to be spent
A refurbishment should normally carry an appropriate allowance for risk and uncertainty.
The amount will depend on the project.
A well-investigated property with a developed and coordinated design presents a very different level of risk from a historic building where significant elements remain concealed and intrusive investigation has been limited.
But there is another important point about contingency:
Having a contingency does not mean you have increased your budget by that amount and are free to spend it.
It is there to manage identified and unidentified risks.
As information improves and risks disappear, contingency can potentially be reduced or reallocated.
Conversely, if new risks emerge, the project team should understand what they could mean for the forecast before making further commitments.
That is much more useful than simply adding a percentage at the beginning of the project and forgetting about it.
So, can you avoid cost surprises altogether?
Probably not.
And anyone promising absolute cost certainty on a complex refurbishment before the building has been opened up should be treated with some caution.
The objective isn't to pretend uncertainty doesn't exist.
The objective is to expose it, quantify it where possible and manage it.
Establish a realistic budget from the outset.
Identify the unknowns.
Investigate the ones that can sensibly be investigated.
Put appropriate allowances against the risks that remain.
Make important decisions early.
Control changes as they happen.
And, throughout construction, keep forecasting the final cost rather than simply reporting what has already been spent.
That's how you turn an uncertain refurbishment into a managed refurbishment.
How we approach refurbishment budgets at Tantallon Projects
Our job as Quantity Surveyors isn't simply to tell you what has been spent.
We want you to understand where your project is heading.
That starts with establishing a realistic budget, understanding what sits within it and identifying the areas where uncertainty remains.
As the design develops, that budget should develop with it. When the project moves into construction, changes and emerging risks should continually feed into the forecast.
When something changes, therefore, the useful question isn't only:
"How much does this change cost?"
It is:
"What does this mean for the final cost of my project?"
That small change in thinking can make an enormous difference to the way a project is managed.
Key takeaways
Refurbishments contain uncertainty. Don't hide it — identify and manage it.
Investigating an unknown before construction can be considerably cheaper than discovering it during construction.
Make decisions that affect other trades as early as possible.
Don't mistake provisional sums and allowances for fixed prices.
Client-supplied kitchens, bathrooms and finishes can work extremely well, but responsibilities for delivery, checking, storage and installation must be clear.
Understand access, logistics and preliminaries when establishing the budget.
Watch the cumulative effect of small changes.
Treat contingency as risk money, not spending money.
Forecast the final cost as you build.
A successful refurbishment isn't necessarily one where nothing unexpected happens.
It's one where the team understands the risks, maintains control and knows what to do when the unexpected does happen.
