Retrofitting an older house: where the real cost surprises hide
Damp that was masked rather than solved, foundations shallower than a modern eye expects, services buried behind old plaster with no drawings — the surprises in an older building tend to be structural and hidden, not cosmetic.
Renovation budgets on older properties go wrong in a consistent pattern: the visible, cosmetic work gets priced accurately, and the hidden, structural work gets discovered mid-project, at exactly the point it's most disruptive and expensive to address. Most of what follows is about recognising the pattern in advance rather than being surprised by it on site.
Damp that's been painted over, not fixed
A fresh coat of paint or a modern plaster skim can hide rising or penetrating damp for years. The tell is usually a musty smell, skirting board deterioration, or damp meter readings that don't match what's visible on the surface. A renovation that strips back finishes without checking for this first can uncover it mid-project, when addressing it properly means far more disruption than it would have at the design stage.
Foundations shallower than modern expectation
Older properties, particularly pre-1900s ones, can have foundations that are little more than a widened base of the wall itself, sometimes only a few hundred millimetres deep — entirely adequate for the loads they've carried for a century, but a material fact if you're planning to extend, underpin, or add significant new load nearby. Worth establishing by trial pit rather than assumption before anything is priced against it.
Services with no drawings, and no reliable memory
Older houses accumulate decades of rewiring, replumbing and reboilering with no as-built record, and cables or pipes get routed through structural timbers or chased into walls in ways that only become apparent once the wall is opened. A renovation budget that assumes services will be straightforward to move is usually wrong, and it's worth holding a specific contingency for services diversion separately from the general one, rather than hoping it comes out of the same pot as everything else.
Asbestos, in more places than people expect
Artex ceilings, old flooring, boiler flues and pipe lagging installed up to the 1999 ban can all contain it. A survey before any older-property renovation that involves genuine disturbance — not just demolition — is worth doing as standard practice, not only where it's obviously suspected, because the areas people least expect to test are frequently the ones that turn out positive.
Structural timber decay behind finishes that look fine
Joist ends built into damp external walls, roof timbers at eaves level where later insulation retrofits have blocked original ventilation, and floor timbers over an unventilated solid floor conversion are all common decay points that don't show from the room side until the finish comes off. None of it is visible from a casual walk-through, which is exactly why it tends to surface once work has already started.
Building a contingency that reflects an older building, not a new one
The same discipline that applies to groundworks contingency on a new build applies here with more force: a renovation contingency on a pre-war property should be sized against the genuine unknowns behind unopened finishes, not borrowed as a generic percentage from new-build practice where far less is actually hidden.