Roof Heat Gain Calculator
In India the roof is the biggest heat collector on the house. See how much heat it lets in — and how much insulation cuts it — from the roof construction, area and temperature difference. The answer comes as heat in watts and the air-conditioning load it adds.
A sunlit roof surface runs far hotter than the air — a dark terrace can be 30–40°C above the room. ~25°C is a fair mid-value; a reflective cool roof lowers it.
= about 2.5 tons of the AC load · 88 W per m².
Two levers cut roof heat: insulation lowers the U-value (above), and a reflective cool roof or a green roof lowers the surface temperature (the ΔT) — best used together.
A planning estimate. It uses indicative U-values and a steady-state heat-gain model (Q = U × A × ΔT); the real load varies with the exact build-up, roof colour/reflectance, orientation, time of day and climate. Use it to compare options and see the value of insulation — a proper cooling-load calculation is qualified MEP work.
Related Guides — Deep-dive reading
Energy-Efficient Facades in India: How the Building Skin Cuts Your Cooling, Heating & Lighting Bills
How a building facade drives cooling, heating and lighting energy in India, the three levers of solar-heat-gain control, insulation and daylighting, U-value, SHGC, VLT and WWR in plain terms, ECBC and Eco-Niwas expectations, and real Indian green buildings.
Building FacadesHeat Transfer in Buildings: How Heat Gets In (and How to Stop It)
The three ways heat moves through a building — conduction, convection and radiation — plus U-values and R-values, why the roof and west wall matter most in India, and why cutting heat gain at the envelope beats fighting it with a bigger air conditioner.
HVAC & CoolingPassive Cooling Strategies for Indian Homes
How to keep a home cool without (much) air-conditioning — the climate-smart design that cuts bills and heat
Design EducationRelated Tools — You may also find these useful
Rainwater Harvesting Calculator
How much rainwater your rooftop can harvest in a year, in litres and kilolitres, from the roof area, your city's rainfall and roof type — with a suggested storage-tank size.
RoofingRoof Area Calculator
The true (sloped) surface area of a roof from its plan footprint and pitch, in m² and sq ft, with a wastage allowance and rough tile/sheet/coating counts — the area you actually buy roofing materials for.
RoofingRoof Pitch Calculator
Convert a roof's pitch between degrees, the rise-in-12 ratio (like 4:12), percentage grade and the slope (area) factor — or work the pitch out from rise and run.
Roofing