Why refurbishment costs more than the quote

Every experienced contractor and project manager in London will tell you the same thing: the quote is not the cost. This is not necessarily because contractors underquote — it is because a significant portion of the cost of refurbishing a building cannot be known until the works begin and the building fabric is opened up.

A realistic refurbishment budget has two components: the contracted sum (what you have agreed to pay for a defined scope of works) and a contingency (a reserve for what you have not yet been able to define). Understanding the difference between the two is the first step to staying in control of your project costs.

What contractors typically find

The most common sources of unexpected cost in London property refurbishment:

  • Structural timber in poor condition. Floor joists, roof timbers, and timber lintels on Victorian and Edwardian properties are frequently in worse condition than visible inspection suggests. Rot, insect damage, and inadequate original sizing are all common.
  • Failed or absent damp-proofing. Properties built before 1920 often have no damp proof course, or one that has failed. Rising damp and penetrating damp are often masked by layers of subsequent decoration.
  • Electrical and plumbing systems beyond economic repair. A full rewire or replumb on a property that appeared to need only upgrading is not uncommon when walls are opened.
  • Asbestos-containing materials. Properties built or refurbished between 1950 and 1985 frequently contain asbestos in artex, floor tiles, pipe lagging, and roof sheets. Once identified, it must be managed or removed by a licensed contractor — costs vary widely depending on quantity and location.
  • Scope creep. It is very tempting, when the walls are already open, to add works that were originally considered out of scope. Every addition needs to be priced, agreed, and recorded formally.

How to structure your contingency

The standard advice — hold 10% as a contingency — is often insufficient on older London properties. A more realistic framework:

  • New build or shell fit-out: 5–10% contingency. The structure is known, the services are new, the unknowns are limited.
  • Modern property (post-1970) refurbishment: 10–15% contingency. Risk of asbestos, and variable condition of existing services.
  • Victorian or Edwardian refurbishment: 15–25% contingency. Structural fabric unknowns, damp, electrical/plumbing condition, and potential asbestos across multiple material types.

A good contractor will flag everything they find as soon as they find it and present options — not just the most expensive one. The contingency is yours to spend or keep, not an invitation to revisit the scope.

The costs nobody budgets for

Beyond the physical works, refurbishment projects carry a number of costs that are frequently overlooked in early budgeting:

  • Party wall surveyor fees (required whenever structural works affect a shared wall)
  • Building Control fees and inspections
  • Skip hire and waste removal (often excluded from quotations)
  • Temporary accommodation costs if you cannot live in the property during works
  • Storage costs for furniture and belongings
  • Snagging and remediation works in the months following completion
The most expensive refurbishment mistakes come from underestimating contingency, not from overpaying for the work itself.