The benefits of a cool roof

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The benefits of a cool roof

Step 10 - Paint Roof Main

On a sunny day, the inside of a black car will be hotter than a white car. It’s similar with a roof. The darker the roof, the more heat it absorbs and the hotter it will be inside your premises.

Painting a roof white or a pale colour, maximises the solar reflectance of a roof – this reduces the amount of heat that is transferred to the building below.

Reflecting heat away from your rooftop can make a significant contribution to preventing heat build-up in your roof space.

According to researchers from the University of South Australia, painting your roof a light colour or choosing a new one that is light in colour, could reduce annual heating and cooling costs by between 4-8%.[1]

Many businesses in Australia have dark-coloured rooftops. These absorb a lot of heat from the sun. In turn, this heats up the workplaces beneath the roofs.

Light coloured roofs can reflect up to 70% of summer heat gain.[2] According to YourHome.gov.au, this is around 50% more than a dark roof. According to Dulux, this has the potential to reduce rooftop surface temperatures by as much as 20–35°C.[3]

This in turn reduces air-conditioning costs as less heat gets transmitted into the business premises below. This is particularly the case when you have air-conditioning ducts running through your roof cavities.

In workshops or warehousing with no air conditioners, having a lighter coloured roof can also make the workplace far cooler and more comfortable for staff.

Australian Ethical Investments (AEI), ACT

With the retrofit of their building, Australian Ethical Investments (AEI) reduced their energy use by 52%, saving approximately $20,000 a year.

 

They utilised double glazing which cut heating demand by around 8% and installed new insulation which reduced the cooling load by 24%.

AEI’s Director Howard Pender said, “The existing building was akin to keeping milk fresh by storing it in a cardboard box. The refurbished building is an esky.”[4]

 

How do you measure the effectiveness of a cool roof?

Step 10 - Solar Reflectance

Image courtesy of the Cool Roof Rating Council.

 

A cool roof should be able to do two things well. As can be seen in this diagram:

  • It should reflect the sunlight away from the building. This is called solar reflectance (SR).
  • The roof should be able to cool itself quickly. This is called thermal emittance (TE).

After reflecting the sun’s heat away from the building, the measure of how much leftover heat has been absorbed is called ‘solar absorptance’ (SA) and it’s measured on a scale of 0 to 1.

If the SA value of a roofing product is near to 1, this means it will absorb more heat into the building than a roof product that is nearer to 0.

The Whitehaven Colorbond Coolmax product below has a SA value of only 0.23. When it comes to keeping a building cooler, it is more effective than the Monument Colorbond roofing product that has a SA rating of 0.73. This lower SA rating will result in lower cooling bills.

Step 10 - ColourBond
 

What are the benefits of a cool roof?

There are numerous benefits in having a cool roof:

  • It can cut your air-conditioning bills.
  • If you don’t have an air conditioner, it may save you having to buy one.
  • It could extend the life of your air-conditioning system.
  • A cool roof can help insulation work more effectively by reducing the heat load in the attic space.
  • It reduces summer peak electricity demand due to air-conditioning.
  • It reduces the cooling load on refrigerators and coolrooms.
  • It makes a workplace with no air-conditioning more comfortable for staff.

Any building can have a cool roof installed on it. During the construction process, you can install a light coloured roof (you should choose a lighter coloured roof regardless of the roofing material that is being used). After construction or during renovation, lighter coloured paints and specialist paint products can also be applied to the roof.

According to the City of Melbourne ‘Cool Roofs’ research report,[5] the following roof types are suitable for this cool roof technology:

  • corrugated iron / zincalume / Colorbond
  • concrete
  • bitumen
  • tile
  • slate

 

Are cool roofs for everybody? 

Although cool roofs are a good solution for much of Australia, if your business is in a region where heating is regularly needed, a cool roof may not be appropriate, as heat absorption via the roof may be of benefit in winter.

Why change the colour of your roof? 

“One thing all business owners can do is to have a lighter coloured roof, known as a cool roof,” says Dr Pockett, from the University of South Australia.

 

“Paint the roof as light coloured as your council area will allow. A cool roof reflects sunlight (including ultraviolet and infrared rays) ensuring the surface will not get as hot during the summer. That leads to less heat entering work spaces. It essentially bounces the heat off of your roof.

 

“Going from a dark to light-coloured roof can decrease your annual energy costs for heating and cooling by 4-8%. With quality reflective paint technology designed to repel dust and dirt, this is a low maintenance roof solution.”[6]

 

Installing reflective sarking under the roof surface will reflect radiant heat and help to reduce heat from entering the building. For reflective sarking to work as a heat barrier, it must have a clear space of at least 20mm between its reflective surface and the underside of the roofing.

 

Before considering changing the colour of your roof, make sure you have maximised your roof insulation for optimum results.

 

Milner Meat & Seafood, NT

At Milner Meat & Seafood in Alice Springs, they applied two coats of white gloss paint to all roof areas to reflect the sun’s heat. This reduced internal temperatures by up to 4°C. For a relatively small cost, this will reduce the need for air-conditioning, saving 5% and almost $2,000 off their annual power bill.[7]

 

Buyer Beware 

Some cool roof product suppliers have made exaggerated claims concerning the value and effects of their product. As such, it pays to check that the product or service has been independently tested and verified.

If you’re looking to paint your roof, employ someone with experience in this area. You should also ask for references from customers who can vouch for their work.

 

For more information

Cool roof products are available from leading paint companies in Australia. There are also a range of specialist cool roof companies. Further information is available via the following links:

The Fifth Estate: Cool roofs versus dark roofs – a special report
EnergyCut.info/cool-vs-dark

Cool Roof Rating Council – cool roof resources and reports from America
EnergyCut.info/cool-roof-rating

Energy Star certified roof products
EnergyCut.info/energy-star-roof-products

Report: ‘Economic comparison of white, green and black flat roofs in the United States’
EnergyCut.info/economic-benefits-white-roofs 

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