Large parts of central and inner London sit inside conservation areas, and a good share of the housing stock is listed as well. Owners often treat that as a planning question to be solved before the build. It is a cost question throughout the build, and as quantity surveyors working in London we price it as one.
The designation does not usually forbid the work. It narrows the acceptable ways of doing it, and the acceptable ways are rarely the cheapest ones.
Windows are the clearest example
Replacing windows on an unconstrained house is a product decision. In a conservation area it becomes a matter of matching the existing pattern, the sightlines, the opening method and often the material. Slim double glazing in a timber sash is a different line in the budget from a standard replacement unit, and the installation takes longer.
Where the building is listed, the window may have to be repaired rather than replaced, which moves the work from a supplier price to a joinery trade with a measured scope.
Roofs, rainwater goods and masonry
The same logic runs through the envelope. Natural slate rather than a substitute, cast metal rainwater goods rather than plastic, lime mortar rather than cement, brick matched to the existing rather than the nearest stock. Each of those is a defensible requirement and each of them has a price.
Lime work also has a programme consequence, because it cannot be rushed in cold weather. A refurbishment that assumes year round working on a lime repointed elevation is assuming something the material will not do.
Consents take time and time is money on a loan
Work that would be permitted elsewhere may need consent here, and where the building is listed, listed building consent sits alongside planning permission. Whether a particular item needs consent depends on the designation and on the local authority, so it has to be checked with that council rather than assumed.
The budget consequence is not the application fee. It is the period during which finance is running and nothing is being built. If the scheme is funded, that period belongs in the cash flow, as covered in preparing a cost plan for a funding application.
Survey work has to come before pricing
On a period building the largest unknowns are behind the finishes. Timber condition, previous alterations, structural movement, services of unknown age and asbestos in places a management survey never reached. None of those can be priced from a drawing.
The sequence that works is survey, then scope, then price. The sequence that fails is price, then survey, then argue. We set out how we handle that in cost control and variations.
Access and scaffolding on a period street
Many conservation areas are made up of narrow streets with no off street parking and footways that belong to the public. Scaffolding a four storey elevation over a pavement needs a licence, a pedestrian route and often a longer standing period than the work itself requires.
Those costs run for the duration of the scaffold rather than for the days the trades are on it, so a weather dependent repair programme extends them. Lime work and scaffolding hire interact in a way that a bar chart drawn in summer rarely anticipates.
Matching is a procurement problem, not just a specification
Specifying a matching brick or a matching slate is straightforward to write and harder to buy. Reclaimed materials come in batches of unpredictable size, and a batch that runs out halfway through an elevation produces a visible join that the planning officer will notice.
The commercial answer is to establish availability before the specification is fixed, and to buy the quantity for the whole elevation at once where the material is reclaimed. That brings forward spend and needs to be in the cash flow.
Where matching proves impossible, the alternative has to be agreed with the authority rather than substituted on site. A substitution made by the contractor to keep going is the kind of decision that leads to enforcement later.
Where the contingency belongs
A refurbishment contingency is not a single percentage applied to the whole job. The new build elements carry ordinary risk. The interface with the existing fabric carries most of the uncertainty, and that is where the allowance should sit.
Writing it that way has a second benefit. When the contingency is drawn down, you can see which assumption failed, rather than watching a single number shrink for reasons nobody records.
What this means for your budget
Expect the specification to be led by what is acceptable rather than by what is available, expect the programme to carry consent periods and weather dependent trades, and expect the survey work to happen before anyone gives you a number worth relying on.
Any figure you see quoted for this kind of work, here or anywhere else, is an example and not a price. The building in front of you decides.
One further point worth planning for. Conservation work tends to produce more variations than new build, because the scope cannot be fully described until the fabric is opened up. That is not a failure of the cost plan. It is the nature of the work, and it is the reason the change control procedure matters more here than on a scheme where everything is drawn.
Agree before work starts how variations will be valued, who may instruct them and how quickly they have to be priced. On a period building those three answers decide whether the final account is a reconciliation or an argument.
Keep a written record of each opening up as it happens, with photographs and the date. On a conservation scheme that record is the evidence behind every subsequent variation, and it is far easier to assemble as you go than to reconstruct at the end from memory and invoices.
Refurbishing a period building in London?
Tell us the address, the designation if you know it and what you want to change. We will set out what has to be surveyed and what the constraints are likely to cost before you commit.