Why top-floor rooms get so hot
A bare concrete or dark-coloured terrace absorbs most of the sunlight that falls on it. Through the afternoon the slab heats up, and because concrete holds heat, it keeps radiating that heat into the room below well into the night. That is why a top-floor bedroom can feel warmer at 10 pm than at noon.
The same daily heating and cooling is also what opens hairline cracks in the slab. So heat and leakage on a terrace are linked: a terrace that moves less, cracks less.
How a cool roof coating works
A cool roof coating is a light-coloured, usually white, top coat that reflects a large share of sunlight back instead of absorbing it. Less heat goes into the slab, so the surface stays cooler and less heat reaches the room underneath. How much cooler the room gets depends on the building: the slab thickness, whether there is any insulation or tiling, how many hours of sun the terrace gets, ventilation in the room and so on. We will not promise a specific temperature drop, but the difference under a light finish is something most families notice in the first summer.
Waterproofing and heat reflection in one job
On a terrace we waterproof, the last layer is a protective top coat, and you choose its colour: terracotta, white or grey. White is the coolest for the rooms below. It costs the same as the darker finishes, so if heat is a problem, choosing white is a free benefit on top of the waterproofing.
What a reflective coat must not do is replace the waterproofing underneath. A thin heat-reflective paint applied straight onto a cracked, unprepared slab will look good for a season and then peel, and the cracks under it will keep leaking. The heat-reflective finish should go on top of a properly prepared and waterproofed surface, as described in our six-step method.
Choosing between white, grey and terracotta
- White: coolest rooms below and a bright, clean look. It shows dust sooner, so an occasional wash keeps it reflecting well.
- Grey: hides stains, sits well next to water tanks and solar frames, and needs the least upkeep, but is warmer than white.
- Terracotta: the traditional terrace red, hides dust and footmarks, and suits older houses, but it gets warmer in the afternoon.
Where it makes the biggest difference
Light roofs help most on single-storey houses and top-floor flats, where the terrace is the main source of heat; on godown and warehouse roofs, where stock is stored under a large slab; and on cold storages, where every degree of heat coming through the roof is energy the plant has to remove. See cold storage waterproofing for those buildings. Towns with long, harsh summers such as Vijayawada, Guntur and Gannavaram benefit most.
Keeping a cool roof cool
A reflective surface only works while it is clean and intact. Sweep the terrace before the summer, wash off dust and bird droppings occasionally, keep outlets clear before the rains, and avoid dragging heavy metal objects across the coating. If you are planning terrace waterproofing anyway, tell us at the site visit that heat is a concern and we will plan the finish around it.