Flat roofs give you more usable solar area than a pitched roof ever will — but only if you can mount the panels without drilling through the waterproofing. On this Longniddry install we used a fully ballasted racking system: weighted aluminium rails sit on rubber pads directly on the roof surface, held down by their own mass rather than by screws into the membrane below.
Why ballasted is the right answer on a flat roof
Any penetration through a single-ply or felt flat-roof membrane is a future leak waiting to happen. Even when done carefully, every bolt is a weakness in the waterproof layer, and every one of them has to be warrantied by whoever installed it. A ballasted system avoids the problem entirely:
- No holes in the membrane — the roof’s waterproofing is left exactly as the roofer left it
- No penetration warranties to argue over later if the roof ever leaks
- Panels can be repositioned or removed without patching holes
- Even load distribution across the roof via broad rubber feet, not point loads through bolts
What we installed
- Solar array on a ballasted rail system, oriented for best generation on the available roof footprint
- 5 kW hybrid inverter — solar, battery, and grid in one unit
- 9.5 kWh battery storage — carries base load into the evening rather than importing at peak tariff
- All cable runs kept above the membrane in UV-rated containment, terminated into proper DC and AC isolation points
What to check before specifying ballast
Not every flat roof takes a ballasted system cleanly. The two things to verify first:
- Load capacity of the roof deck — ballast adds weight (usually 15–25 kg per square metre depending on wind zone). A structural review is part of the quote, not an afterthought.
- Wind uplift calculations — panels on a flat roof catch wind. Ballast is sized to the site’s wind zone, not picked out of a catalogue.
Both of those were signed off before a single rail went on the roof.
Outcome
Commissioned September 2025. The system has now run through a full Scottish winter and back into spring — generating through the long summer days, carrying evening loads on stored energy, and leaving the roof membrane exactly as it was before we arrived.