Retaining an existing frame: the retrofit appraisal

Retaining existing structure in a planning application is now an evidence question rather than a design preference. Where an adopted plan expects reuse before demolition, the authority will ask you to prove that retention was tested properly, and a two-page condition report concluding that the building is "in poor repair" will not carry that burden. What carries it is an appraisal that quantifies the existing frame's capacity, says what adaptation would cost in buildable terms, and sits alongside carbon evidence that uses the same assumptions.

The reverse case matters too. Where you intend to retain, the appraisal is what turns an intention on a drawing into a condition the authority can enforce.

Policies that expect reuse before demolition

There is no single national retrofit-first policy. The expectation is assembled from several places, and which ones apply depends on where the site is.

The Framework supports making effective use of land and resources and expects the efficient use of existing buildings. Beyond that, a growing number of adopted local plans and supplementary documents contain explicit sequencing: demonstrate that retention and refurbishment have been considered, and justify demolition by reference to carbon, condition and deliverability. In London, whole life carbon assessment and circular economy reporting apply to referable schemes under the London Plan, and several boroughs have gone further in their own plans. Read the adopted wording for your authority rather than relying on a general principle, because the policies differ on whether the test is sequential or a matter of weight in the balance.

Two procedural points sit alongside. In a conservation area, demolition of a building is itself development requiring permission, so the demolition and the replacement are assessed together rather than the demolition being assumed. And on sites where the replacement would be a relevant building for Planning Gateway One purposes, the fire strategy becomes an application-stage document rather than a later one.

What a retention appraisal has to contain

A structural appraisal written for a planning audience is a different document from one written for a purchaser. It has to answer the planning question: could this frame carry the intended use, and at what cost in floor area, programme and carbon.

Six elements make it usable.

1. The existing structural form, described element by element: frame material, grid dimensions, floor construction, lateral stability system, foundation type and depth where known.
2. The design codes the building was built to, and the imposed loads it was designed for, taken from record drawings or inferred and labelled as inferred.
3. Condition evidence from intrusive investigation, not visual inspection alone: concrete cores and compressive strength, cover and carbonation depth, chloride content where the structure is exposed, reinforcement scanning, steel coupon tests and weld inspection on older steelwork.
4. A capacity assessment for the proposed use, including the disproportionate collapse requirements that now apply.
5. The adaptation works required, with their consequences for floor-to-floor height, usable area and servicing routes.
6. A clear statement of what remains unknown and what further opening-up would resolve.

The sixth element is the one that gives an appraisal credibility. A document that claims certainty about a 1960s frame from a dozen core samples invites challenge. One that identifies the residual risk and proposes a staged investigation is far harder to argue with. The detailed mechanics are covered under structural appraisal of a building proposed for retention, and the planning-facing version draws on the same investigation.

Capacity, condition and adaptability

Three different tests get conflated, and separating them sharpens the argument.

Adaptability defeats more conversions than condition does. A mid-century office frame with 3.3 metre floor-to-floor and a 9 metre grid will often take residential loads comfortably and still fail as housing, because the raised floor, the downstand beams, the acoustic separating floor and the mechanical ventilation leave a ceiling height that will not satisfy space standards. Say that plainly with dimensions rather than describing the building as unsuitable.

Disproportionate collapse is the technical issue that most often turns a straightforward retention into an expensive one. Buildings above a certain height fall into a consequence class that requires horizontal and vertical tying, and retrofitting that tying into an existing frame with limited bearing lengths can mean working on every floor plate. Price it, because it changes the answer.

Foundations deserve their own section. Reusing existing foundations under increased load, or threading new foundations between old ones, is where the programme risk sits, and the ground investigation has to be designed for that question rather than for a generic desk study. The constraints are the same ones that govern existing foundations and basement depth.

Where carbon evidence meets structural evidence

The two documents have to use the same numbers. An appraisal that assumes 60 per cent of the frame is retained, sitting next to a carbon assessment that models full retention, destroys the credibility of both.

Assess the substructure and frame as a distinct part of the Whole Life Carbon Assessment rather than letting them disappear into a building-wide total, because those elements carry the largest share of upfront embodied carbon on most buildings and they are the elements retention actually saves. Report the modules separately so the reader can see which savings come from avoided new material and which from avoided demolition and disposal.

Three alignment checks are worth running before submission.

• The retained quantity in the carbon model matches the retained elements in the structural drawings, tonne for tonne.
• Strengthening works appear as new material in the carbon model, because they usually are.
• The assumed design life is the same in both documents, since the maintenance and replacement modules depend on it.

Carbon assessment under the current RICS methodology is work councils expect a suitably qualified author to do, and professional review is strongly advised.

When retention does not work

A refurbishment case can be wrong, and saying so with evidence is better than producing a retention scheme nobody intends to build.

The arguments that hold up are specific. The frame cannot carry the use without strengthening that exceeds the value of the material saved. The geometry cannot deliver the floor area the site needs under the development plan's own density expectations. The fabric cannot reach the thermal standard required without losing internal area or altering an elevation the authority wants kept. The remediation of contamination or asbestos within the structure makes staged occupation impossible.

The arguments that fail are general. Age. Appearance. Market preference for new floorplates. Commercial obsolescence stated without a viability case. And a demolition programme presented as fixed because the contractor has priced it that way.

Presenting options rather than a conclusion

An appraisal that offers one answer reads as advocacy. An appraisal that sets out three or four options with their consequences reads as professional judgement, and officers respond to it differently.

Set out full retention, partial retention of frame and substructure, facade retention where relevant, and full redevelopment. For each, give the net internal area achieved, the floor-to-floor outcome, the upfront carbon, the programme and the residual structural risk. Then state your recommendation and why, and be willing to have it tested.

Partial retention is the option most often missing and most often the right answer. Keeping the substructure, the basement and the lower frame while rebuilding above delivers much of the carbon saving without the geometry compromise, and it is easier to condition than a facade retention scheme.

Securing the retained frame

Retention promised in a planning statement and not secured by condition is worth nothing once the site changes hands.

Three conditions do the work. A condition requiring development in accordance with the approved structural drawings, with the retained elements identified on a specific drawing number. A pre-commencement condition requiring a temporary works and protection method statement for the retained structure. And a condition requiring any proposal to remove a retained element to be approved in writing, with updated carbon evidence, rather than treated as a minor amendment.

Where the retained structure also affects the fire strategy, the Fire Statement for a relevant building must be prepared by someone with the necessary fire-engineering competence under the Building Safety Act 2022 framework and Article 9A of the Development Management Procedure Order 2015. A drafted document is a starting point for that engineer rather than a substitute for them, and the same is true of the Structural Survey that sits behind the appraisal.

Enter your postcode on PlanScope to see which reports a refurbishment or redevelopment on your site is likely to need.

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