Data from 1,568 roof planes shows the solar array is usually the smaller load on a roof. Snow, and the altitude that drives it, decides how much room is left, and that should shape where an estate starts writes Sahir Raihan, Structural Engineer and Managing Director, Solar Surveys
Ask what might stop a rooftop solar project and most people point at the panels. There are a lot of them, they look heavy, and they stay up there for decades. In practice, the array is rarely what decides whether a roof can take it.
We have put numbers on this. The UK Roof Plane Dataset 2026 records 1,568 roof planes on 651 buildings and homes assessed for solar between January and September this year, with every figure taken from an issued structural report. These are roofs somebody intended to put solar on, not a random sample of UK stock, which makes them a fair picture of the projects energy managers are actually weighing up.
The array is the smaller load
A typical array adds about 0.13kN/m². On the median commercial roof in the dataset, the allowable imposed load was 0.60kN/m², so the array takes about a fifth of what the roof is allowed to carry. The design snow load on that same median roof was 0.40kN/m², around three times the array. On most roofs it is the snow that uses up the capacity, and the panels sit on top of it. The same holds on homes, where a typical array is about 17% of the allowable imposed load.
Altitude sets the headroom
Capacity used here means the combined PV and snow load as a share of what the roof is allowed to carry; what remains is the headroom. Snow load rises with altitude, and the effect on capacity is large. The median design snow load on commercial roofs went from 0.34kN/m² below 50m above sea level to 0.56kN/m² at 150 m and above. Over the same range, the median share of a commercial roof’s capacity used by PV and snow together rose from 61% to 92%. On homes the climb was steeper, from 51% to 96%, as the roof snow load more than doubled over the same range.
So two identical buildings can give different answers purely because of where they stand. A shed on a low-lying business park may have room to spare; the same shed on high ground may have very little.
Where the margin is thinnest
Across the commercial roofs, the median used 71% of its capacity once PV and snow were combined. Of 112 commercial buildings with a stated figure, 20 used 90% or more. Schools and faith and community buildings reached that level most often, 36% of each. Many are older buildings, and they are where careful early assessment pays off most.
Housing shows the same pattern at street level. In one North East postcode area the median home used 59% of its capacity; in another, 96%, with 87% of homes there at or above 90%. Two estates of very similar houses can need quite different answers.
What it means for a business case
A generic snow load, or one taken without the altitude correction, makes feasibility work optimistic on exactly the sites with least headroom to spare. For anyone planning solar across an estate, three things follow:
The panels are the part everyone can see. The headroom they need is set by the snow the roof was designed for, and by where the building stands. Get that right at the start and the business case holds up.
Sahir Raihan is a structural engineer and the Managing Director of Solar Surveys Ltd, which assesses whether roofs can carry solar PV across the UK and Ireland. The UK Roof Plane Dataset 2026 is free to read and cite at solarsurveys.co.uk/roof-plane-dataset-2026
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