The record is not the building
Most existing buildings come with drawings of some kind: original construction drawings, a landlord’s record set, or a survey done for a different purpose. All of them describe an intention at a moment in time, and the building has been altered since.
Alterations are rarely recorded well. Partitions move, services are rerouted, openings are formed and slabs are penetrated, and none of it makes its way back to the drawing. Measuring from a record set therefore produces quantities for a building that is not the one you own.
The practical consequence is that the first task on a refurbishment is establishing what is actually there, and it is a measurement task rather than a design task.
Age changes the problem rather than simply increasing it. A building from the last thirty years usually has a record set that is broadly right and services that are documented. An older building may have no reliable record at all, but it may also have a simpler structure that is easier to read once opened up. Neither is automatically the more expensive proposition.
What the survey has to cover
A measured survey establishes dimensions, levels and the position of what can be seen. That is necessary and not sufficient, because the cost sits in what cannot.
Alongside it the questions are structural, meaning whether the existing frame or walls take the new loading and what the foundations are. Services, meaning age, capacity, condition and whether anything can be retained. Fabric, meaning the make up of walls, floors and roof. And materials, meaning asbestos and anything else with a specific regime attached. [VERIFY: the current statutory duties applicable to asbestos management and survey type for the building in question.]
Each answer either removes a cost or converts a guess into a number. Both are progress.
Opening up is cheaper than assuming
Some questions cannot be answered without breaking into the fabric, and opening up is resisted because it damages a building somebody is still using and costs money before the scheme is committed.
The comparison worth making is against the value of the assumption it removes. A structural opening up exercise costing a few thousand pounds settles whether a slab needs strengthening, and that answer moves a figure by a different order of magnitude entirely.
Where opening up genuinely cannot happen before purchase, the honest treatment is to carry a stated risk allowance with the trigger written down, rather than a cost plan that quietly assumes the favourable answer.
Measuring for the pricing document
Once the building is understood, the measurement itself follows normal standards, with one difference: descriptions have to record the context as well as the work. Removing a partition in an occupied building on the fourth floor with no goods lift is not the same item as removing a partition on an open site, and a description that omits the context will be priced as though the context does not exist.
This is where refurbishment bills go wrong most often. The quantities are right and the descriptions are thin, so the tender is priced against an easier job than the one that exists.
What it does for the contract
A properly surveyed and measured existing building lets you write a pricing document that transfers risk knowingly. Items that are understood can be fixed price. Items that remain genuinely uncertain can be provisional sums or defined risk allowances.
Without the survey, everything is uncertain, so either the contractor prices for the worst case or the employer carries the lot. Neither is a commercial position anybody chose.
What this means for you
Budget for surveys as the first line of the cost plan, not as a precursor to it, and get them done before the figure you are relying on hardens into a commitment.
Where a building has to be priced with incomplete access, say so on the face of the cost plan and value the risk rather than assuming it away. That approach is described on our client side quantity surveyor page, and the measurement discipline behind it on quantities and take-off.
One practical sequencing point. Book the intrusive surveys as early as access allows, because they are the ones with lead times attached: specialist attendance, scaffolding, permits and making good. A structural opening up exercise that could have happened in week two frequently happens in week ten, and by then the cost plan has already been issued and believed.