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White Roofs on Townsville Buildings

Scientific analysis shows that a white roof can substantially reduce air conditioning loads and make buildings more comfortable.

see credits and disclaimer

Peak air conditioning loads in buildings with galvanised roof can be four times as large as for a white roof
  • Lower air conditioning costs

  • More comfortable homes

  • Cooler living spaces

  • High solar reflectance

  • Low heat conductivity

Until several years ago engineers were rarely able to calculate the response of a building that is subject to time varying interior and exterior thermal loads. This is because a large number of simultaneous equations were required. However, with the advent of inexpensive computing power and specialist software, thermal modeling of buildings is now possible.

For example, Engineering Equation Solver (EES) is able to solve large sets of non-linear algebraic and differential equations.

In this web page is presents an overview of the the use of EES to investigate the effect of roof colour / surface finish on human comfort and air conditioning load on a model building representative of a North Queensland home.

The computer model building used for this assessment has no windows and its thermal response is driven solely by solar radiation on the roof surface.

The model building features:

  • 100mm concrete slab
  • 2.5m high concrete block wall
  • 13mm thick plasterboard ceiling
  • 125mm attic airspace and 1mm steel roof
  • the steel roof is assumed to have a thermal emissivity of 0.05, approximates a reflective foil below roof surface

White roof and green roof side by side. Townsville buildings are rarely energy efficient.
White roof and green roof side by side.
Townsville buildings are rarely energy efficient.

Despite common belief that galvanized metal surfaces reflect solar radiation, corroded (weathered) galvanized surfaces absorb up to 80% of sunlight. Moreover, radiative heat loss to the sky is very low.

Combining high solar absorbance with low thermal heat loss produces roof surface temperatures can reach nearly 60 degrees Celsius.

On the other hand, the temperatures of a white roof under similar conditions stay below 35 degrees Celsius.


  • Adding insulation with an R-value of 4msq.K/W could reduce the air conditioning load for the building with galvanized roof to a similar level as for the un-insulated white roof building.
  • It is expected that the air-conditioning load for other roof colours, except black, will lie somewhere between that of buildings with white and galvanized roof.
  • The calculations suggest that peak air conditioning loads due to solar heating in buildings with galvanized roof can be four times as large as for a white roof (with reflective foil laminate)
  • Assuming an air-conditioner with a COP of 2.0 and electricity cost of 10c/kWh annual air-conditioning costs would vary from $493/annum for a galvanized roof to $98/annum for white roof building.

Time to choose: roof under construction.
Time to choose: roof under construction.

Credits and Disclaimer:

This web site is an overview of:
Thermal Performance of a Building using Engineering Equation Solver
Presented at Northern Engineering Conference, Cairns (7-10 June, 2001)
Engineering Innovation and Sustainable Energy.

Harry Suehrcke

James Cook University
School of Engineering
Townsville, Queensland, 4811, Australia

Disclaimer: This information is made public upon request by Townsville City Council. The paper has not been fully peer reviewed. Users of the information in this overview report do so at their own risk.

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