Budgeting a conversion: structural and asbestos surveys

Conversion survey costs are mostly decided by one choice: whether the survey is allowed to open things up. A visual inspection of a 1960s office or a Victorian chapel will tell you what is visible and exclude everything else, which is the lowest priced report and the one that produces the nastiest surprises. An intrusive survey, with trial holes to the foundations, finishes removed in sample locations and samples taken for analysis, costs more and makes the appraisal real.

For a conversion, pay for the intrusive version. The saving on the survey is trivial against the cost of discovering on site that the floor will not take residential loading.

Structural appraisal and opening up works

A structural appraisal for a conversion answers a different question from a condition survey. It asks whether the existing structure can carry the proposed use and the proposed alterations.

The items that matter:

• floor construction and capacity, which decides whether a commercial floor can take residential or assembly loading
• roof structure, and whether it can carry new insulation, finishes or a loft floor
• wall construction, including whether the external walls are solid, cavity or a non-traditional system
• lateral stability, particularly where large openings are proposed
• the condition of embedded timber at wall plates, bearings and joist ends
• foundation depth and width where any new load is added

Opening up is how most of those are established. Expect lifted floorboards or small slab breakouts, removal of ceiling sections, endoscope inspection into cavities, and sample removal of plaster. Agree in advance who makes good afterwards and at whose cost, because that line is left out of a surprising number of appointments.

Where the authority wants structural evidence with the planning application, usually on a barn or chapel conversion, the submitted document is a Structural Survey from a suitably qualified author. Councils expect an engineer's appraisal rather than a general condition report, and professional review of any draft before submission is strongly advised.

Trial holes and foundation investigation

Trial holes are the item most often cut from a budget and most often needed.

A hole dug against the existing footing establishes its depth, its width, the material it is built from and the ground it bears on. That tells the engineer whether a new extension foundation can match it, whether the footing needs strengthening from below, and whether a nearby tree has already influenced the ground.

Three practical points. Hand dig against the building rather than machine excavating, because the aim is not to weaken what you are investigating. Record the ground profile as well as the footing dimension, since the soil type determines foundation depth under the current guidance. And photograph everything with a scale in shot, because the photographs become the evidence when a contractor later prices the work.

Where the ground is in question as well as the foundation, a wider ground investigation follows, and that is a separate commission with its own competence requirements.

Refurbishment and demolition asbestos surveys

Any building constructed or refurbished before 2000 should be assumed to contain asbestos until a survey shows otherwise. The legal framework is the Control of Asbestos Regulations 2012, and two survey types matter.

For a conversion the refurbishment and demolition survey is the one you need, and it has to cover the areas where work will take place. It is destructive by design: ceilings opened, ducts entered, floor finishes lifted, service risers inspected. For that reason it is normally carried out in a vacated building, which affects programme on a tenanted property.

The places asbestos most often turns up in conversion projects: textured coatings on ceilings and walls, floor tiles and the bitumen beneath them, insulating board behind panel heaters and around service risers, cement sheets in roofs and soffits, rope and gaskets in old boiler installations, and sprayed coatings to structural steel.

The survey report should give a register with locations, material types, condition and recommended action. What it cannot do is price the removal, and the removal is where the money is.

Where a survey changes the scheme rather than confirming it

Four findings regularly turn a conversion appraisal upside down.

Floor capacity below the required loading for the new use, which means either strengthening every floor or revising the layout so that heavy loading sits where the structure allows.

Non-traditional construction, where the walls or frame are a system type that cannot readily take new openings or additional load without specialist advice.

Sprayed asbestos coating to a steel frame, which requires licensed removal in a controlled enclosure. That is a programme item measured in weeks, with implications for access, scaffolding and sequencing.

Foundations shallower than required for the new load, pushing the project into underpinning, which is costly, slow and disruptive to neighbours, with party wall implications of its own.

Each of these is far better known before exchange on the building than after. If a vendor refuses access for intrusive investigation, price the risk into the offer rather than assuming the best case.

Sequencing surveys against the application

An order that avoids abortive spend:

1. Structural appraisal, visual, at the appraisal stage, enough to decide whether the building is a candidate.
2. Asbestos management survey if you need to know what is there before committing, which is often part of due diligence.
3. Intrusive structural investigation including trial holes, once you have access and before the design is fixed.
4. Design and planning application, informed by both.
5. Refurbishment and demolition asbestos survey after the building is vacated and before any works, covering the specific work areas.
6. Building control submission with structural calculations.

The asbestos survey belongs late because it has to match the actual scope of works, and a survey carried out against an earlier scheme will not cover the areas the final design touches. The structural investigation belongs early because it changes the scheme.

Where demolition or significant stripping out is involved, a Pre-redevelopment Audit records what is in the building and what can be reused, and a Site Waste Management Plan deals with how material leaves the site. Hazardous material has its own disposal route and documentation, which is a cost line rather than an afterthought.

Costs that only appear once work starts

Budget separately for the things a survey identifies but does not price.

Licensed asbestos removal, which must be carried out by a licensed contractor and notified to the regulator in advance of the work, with the notification period built into the programme. Non-licensed and notifiable non-licensed work has its own rules and is still not a job for a general builder.

Making good after intrusive investigation, both the structural opening up and the asbestos survey.

Temporary works and propping, designed rather than improvised, wherever structure is being removed.

Hazardous waste disposal, with consignment documentation.

Service disconnections and diversions, which turn up once ducts and risers are opened and the actual routes become visible.

Building control charges under the current regime, which sit alongside the planning fee as a separate line, as our note on building control charges alongside the planning fee sets out. Utility and drainage connection charges are a further line again, covered in our note on water and drainage connection costs on a small site.

Contingency that reflects what the survey did not see

Set contingency against uncertainty rather than against a habit.

The questions that should drive it: how much of the structure was actually inspected, whether trial holes were dug or foundations assumed, whether the asbestos survey was intrusive within every area to be worked on, whether the building has been altered since construction without records, and whether any area was inaccessible on the survey date.

An older building with full intrusive investigation can carry a lower contingency than a 1970s building surveyed visually, because age matters less than knowledge. Write down each assumption the surveys left open, with a note of what it would cost if the assumption is wrong. That list is the contingency, and it is far more useful to a lender than a round percentage.

Pay for the trial holes and the intrusive asbestos survey before you fix the design, not after. See PlanScope pricing for what the supporting planning documents cost to draft once the survey work is in hand.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. For specialist technical reports, qualified professional input may be required. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.