SOLAR CARPORT STRUCTURAL ENGINEERING
The canopy is the structure. The array is the load.
A solar carport gets specified as a solar product and built as a canopy. Structurally it is the second of those: a large roof plane standing on its own columns, with nothing above or around it to shelter it and air moving freely over both faces. The modules add relatively little weight. What decides the design is what the wind tries to do to that plane, and whether the foundations can hold it down.
Canopy and foundation design is long-standing core work for our engineers, well beyond solar. The discipline transfers directly. What is specific to a solar carport is the load case the array imposes and the fact that it has to keep working for twenty-five years over occupied parking bays.
01 · THE GOVERNING ACTION
Uplift on a free-standing roof, not weight on a slab
Wind actions on a canopy are derived under BS EN 1991-1-4 and its UK National Annexe as a free-standing roof, which is a different treatment from a roof on an enclosed building. Air passes over the top surface and under the soffit, and the design case is the net pressure across the plane.
For most carports the critical condition is uplift rather than downforce. That reverses the intuition the structure invites: the thing to worry about is not the canopy being pushed down onto the cars, it is the canopy trying to leave. Overturning at the columns and tension in the foundations follow directly from it.
Where a canopy is open on all sides, and particularly where it sits on an exposed edge of a site or an upper deck, the coefficients and the resulting uplift are not comparable to a sheltered arrangement. The exposure has to come from the site.
02 · ACCIDENTAL ACTIONS
Columns stand where vehicles move
A carport column is a structural element positioned in a trafficked area, so accidental impact is a design situation rather than a hypothetical. It is assessed under BS EN 1991-1-7.
There is more than one legitimate answer. The column can be designed to take the impact, it can be physically protected, or the layout can keep it out of the swept path. What is not acceptable is for the question to go unasked, because the consequence of a column failing under impact is a roof plane coming down over occupied bays.
03 · WATER AND SNOW
Everything that lands on it has to go somewhere
A canopy collects precipitation across its entire plan area and discharges it at an edge. On a tilted canopy, snow will also shed. Neither should be resolved by allowing discharge across the parking bays, the pedestrian route or a doorway.
Snow actions are derived under BS EN 1991-1-3 and its UK National Annexe using the site’s own altitude. On a tilted canopy the loaded case is not necessarily uniform, and where modules create local obstructions accumulation can concentrate rather than spread.
Drainage is a structural question as well as a serviceability one, because ponding on a shallow canopy adds load exactly where the plane is least able to take it.
04 · FOUNDATIONS
A car park build-up was not designed to be pulled upwards
Carport foundations sit in ground that is usually already occupied — sub-base, drainage, ducts, lighting and often live services. Available depth is limited and the excavation is rarely unconstrained.
Against that, the governing action is frequently tension rather than compression, because the wind case is trying to lift the canopy. A foundation sized for the weight of the structure is not necessarily a foundation that resists uplift, and the two checks are not interchangeable.
Where the design depends on the mass or the passive resistance of the surrounding ground, that assumption should be stated and checked rather than inherited from a standard detail.
05 · WHAT WE PROVIDE
Deliverables
- Wind actions on the canopy as a free-standing roof, with the governing combination named under BS EN 1990
- Frame, roof plane and column assessment, including the uplift and overturning case
- Accidental impact assessment at the columns under BS EN 1991-1-7
- Snow and drainage assessment, including where discharge and shedding are directed
- Foundation design against tension and overturning within the available build-up
- Calculations and a stated conclusion, reviewed and signed by a qualified structural engineer
Quotations to a 24-hour target, reports to a 48-hour target from confirmed scope. £5m professional indemnity cover in force.
FREQUENTLY ASKED
Solar carport structural questions
What governs the structural design of a solar carport?
Wind uplift, in most cases. A carport roof is a large free-standing plane with airflow on both faces, so net uplift under BS EN 1991-1-4 and its UK National Annexe usually governs the frame and the foundations rather than the weight of the modules, which is comparatively small.
Does vehicle impact need to be considered on a solar carport?
Yes. Columns in a trafficked area are exposed to accidental impact actions, which are assessed under BS EN 1991-1-7. That may be resolved by the column design itself or by physical protection, but it should be an explicit design decision rather than something left out.
Where does the water and snow go?
Somewhere deliberate. A canopy collects precipitation over its whole plan area and discharges it at the edge, and a tilted canopy will shed snow. Both need to be directed away from parking bays, walkways and doorways rather than allowed to discharge across a circulation route.
Have you designed canopy structures before?
Canopy and foundation design is long-standing core work for our engineers, across commercial and industrial projects. The structural discipline is the same whether or not the canopy carries modules; what is specific to solar is the load case above it, which we derive from the array rather than assume.
THE WIDER STRUCTURAL SCOPE
One engineering team, roof to ground
Carports rarely arrive on their own. They come attached to a rooftop scheme, a ground-mount field, or a battery installation that needs a base. The structural standard should not change depending on which part of the site is being looked at.
Ground-Mount Structures Rooftop Structural Surveys Published Research
Uplift Resolved.
Columns Checked.
Carport, ground-mount and rooftop structural engineering for solar PV across the UK, signed by a qualified structural engineer.