Heatwaves & Reflective Rooftops 20.12


Rooftop of Unit before Solar panels installed

During the heatwave preceding Black Saturday in February 2009 we were living in our solar powered stand-alone house in the bush. Normally the mudbrick construction with walls 20cm thick was reasonable insulation. The cathedral roof had a small, and as it turned out, inadequate air space insulated with foil. But the series of hot days of over 40 degrees with nights not that much cooler meant that after 3 days the heat inside the house at 6am in the morning was still about 33 degrees. Basically intolerable. With our stand-alone system there were power restraints and thus no air conditioner – just 2 small portable fans draped with damp cloths.

The solution we adopted was to get the iron roof painted with white reflective paint. This is geo-engineering on a very small scale – but one practiced for hundreds of years in the Greek islands with their regularly white washed cottages and town buildings. The job was done by the contractor in about 3 hours and the results were highly satisfactory. The roof temperature difference was an amazing result for such a simple action. After the job had been completed I could easily hold my hand down flat on the painted surface but a small piece of exposed iron was far too hot to handle. The downside was that the house was cooler in winter thus requiring some heating or an extra jumper on the occasional frosty morning. It is apparent that the winter is also getting warmer although every now and then we still experience an extreme cold event. The exercise to make the house still liveable in very hot weather was successful.

After moving to our retirement unit in town we have repeated the process. The tiled roof was restored and painted with reflective paint (though cream rather than pure white) before our solar panels were installed. To this we have added extra insulation, a reverse cycle air-conditioner and are working on window curtains and shades. Now with grid connected power all this is fine until the grid fails. Hopefully the insulation, draught proofing and other features will be functioning well and ameliorate the heat when this occurs.

When passing through suburbia on our way to the city we see plenty of PV panels and solar hot water systems. But mainly we see endless numbers of large oversized houses, with no eaves and dark roofs – an architectural folly unprepared for the increasing number of heatwaves we are only beginning to experience.