Research · Paper 03 · August 2026
Across roofs where a condition assessment was carried out, 82% showed defects capable of affecting long-term waterproofing performance. That figure is not primarily a solar finding. It is a statement about the building stock, and it has a consequence for anything mounted on top of it.
Of roofs where a condition assessment was carried out showed defects capable of affecting long-term waterproofing performance.
Of the 575-roof dataset had a condition assessment carried out, so the finding rests on the substantial majority of the sample.
Period over which the roofs were assessed, across the United Kingdom.
01 · The finding
The test applied is whether a defect or maintenance issue is capable of affecting long-term waterproofing performance. It is a functional test rather than a cosmetic one, and it is deliberately broad, because the things that let water into a commercial building are various and individually unremarkable.
Recorded under this testSurface weathering and deterioration of the covering · cracking · missing, cracked or degraded rooflights · vegetation growth · inadequate or failed weatherproofing detail · and general lack of maintenance. Each is recorded where present and where it bears on the ability of the roof to keep water out over its remaining life.
A narrower test — active leaks only, say — would produce a smaller and more dramatic-sounding number while describing something less useful. Roofs rarely fail suddenly. They accumulate small failures, each individually tolerable, until one of them stops being tolerable. A test that only counts the last one arrives too late to be of any use to an owner.
The dataset records whether the test was met. It does not carry a validated breakdown by defect category, so no such breakdown appears here. How much of the 82% is weathering as against rooflights as against vegetation is not something we can state, and stating it would be inventing precision the record does not hold.
02 · The consequence
A roof covering has a remaining service life. So does an array, a set of plant, or a screening system. They are almost never installed at the same point in those two lives, and nobody reconciles them.
Put a twenty-five year asset on a covering with eight years left and a problem has been created that surfaces in year eight: the covering has to be replaced with the asset sitting on it. Somebody strips it, recovers the roof, and reinstates. That cost appears in no yield model, no lease and no power purchase agreement we have seen.
A structural appraisal answers whether the roof can carry the load. A condition assessment answers how long the covering has left. A roof can pass the first and fail the second, and the second is the one that determines whether the installation was a good idea. Both questions have to be asked, and asking only the structural one is the more common error.
If most roofs assessed carry defects capable of affecting waterproofing performance over their remaining life, then the covering question is not a rare complication to be handled when it arises. It is a standing feature of the stock, and a process that does not ask it will get it wrong most of the time.
03 · What to do with it
Not its age, and not whether it is currently leaking. Its remaining life, stated as a judgement with the reasons behind it. This is the number that has to be compared against the design life of whatever is going on top.
There are three honest answers: recover the roof first, accept and price the future removal and reinstatement, or do not install. All three are legitimate. Discovering the question after commitment removes the first and makes the second considerably more expensive.
Where a lease or an agreement runs twenty years and the covering has eight, the cost of removal and reinstatement falls somewhere. That allocation is a contractual question, but it is one nobody can answer without the first two.
04 · Basis and limitations
05 · Citation
Suggested citation
Raihan, S. (2026) The Condition of UK Commercial Roofs. Solar Surveys Research, Paper 03. Solar Surveys Ltd. Available at: https://solarsurveys.co.uk/research/the-condition-of-uk-commercial-roofs
Published under Creative Commons Attribution 4.0. Reproduce, quote and build on this with attribution. Writing about it and want something clarified, or a point expanded? Ask. We would rather it was reported correctly than quickly.
Solar Surveys Research
Roof condition assessments and on-site structural surveys for commercial buildings across the UK, signed by a qualified structural engineer.