Solar Panels on Concrete Flat Roofs

It depends on the method and on the condition of the existing waterproofing. A ballasted system that doesn't drill the slab at all adds no leak risk from the installation. A drilled system needs the waterproofing repaired around every fixing point, which is standard practice and works — but it has to be done correctly. The point we always stress is that if the roof already leaks, that has to be fixed before installation, not after, because fixing it later means taking the panels off.

Yes, but the waterproofing has to be repaired first, and we tell you this at the site survey. If panels go on top of waterproofing that has already failed, then when a leak appears later there's no way to tell whether it came from our fixing points or from the old waterproofing. Repairing it first keeps the record clear for both sides. Waterproofing repair is a cost that has to come first, so we list it separately in the quote where you can see it.

In Southern Thailand we usually keep the tilt fairly low, because close to the equator the angle that gives the most energy over a year is in the low range, and a steep tilt means wider gaps between rows, so fewer panels fit. But a tilt that is too flat stops rain from washing the dust off and leaves water sitting at the panel edges. So we pick an angle that balances total energy, the number of panels that fit and drainage, and show you the numbers for both options before you decide.

Because panels on a flat roof are tilted, each row casts a shadow behind it. If the rows are too close, the front row shades the one behind in the morning and evening, when the sun is low. Strip shading like this makes panels wired in series lose more power than the shaded area alone would suggest. We calculate the spacing from the tilt and the latitude of the site, which is why a given roof fits fewer panels than most people expect.

Panels on a flat roof take more wind uplift than panels lying flush on a pitched roof, because they are tilted and wind can get underneath them. The taller the building, the stronger the wind compared with ground level. So we calculate wind loads from the actual building height and location, rather than using the same standard figure as a single-story house. A ballasted system needs enough ballast for the calculated uplift, and a drilled system has to anchor into structure that can genuinely resist the pull-out force.

That has to be checked at the site survey. Flat roofs are built with a slight fall so water drains to the outlets. If ballast blocks or bases sit across the flow, water ponds on the roof, which speeds up the deterioration of the waterproofing and can cause leaks later. So we look at how the water flows and where the outlets are before laying out the panels, and keep the drainage paths clear.

Shophouse roofs are usually long and narrow, and neighboring buildings of different heights often cast shade at certain times of day. So we assess both the area that can really be used after row spacing and maintenance walkways, and the shade from surrounding buildings through the day. Together these usually mean noticeably fewer panels than you'd calculate from the bare roof area. We give you the real figure at the site survey.

Our installation work carries a 2-year warranty, which covers leaks at the points we drill and the waterproofing we repair. It doesn't cover leaks from the roof's existing waterproofing. That's why we inspect and photograph the existing waterproofing before every job starts. If it has deteriorated, we ask for it to be repaired first — we don't install on top of an existing problem.