In the overlap while building our new house I had the opportunity to do temperature logging in the roof of both houses at the same time to see how they compared. The old house is a dark grey concrete tile roof with no sarking, while the new house has a white colorbond roof (surfmist) with foil-backed fibreglass insulation under the sheets (like Bradford Anticon)
Here's a plot of the temperature logs for a couple of warm days in Adelaide in March:
I measured the temperature at the bottom of the roof space, just above the ceiling insulation. It would probably get hotter in both cases as you rise up the space, but the temperature up there is less relevant to the thermal performance of the house. The spike in the outside temperature on the 2nd morning was from when the thermometer was caught by the sun for a bit.
The first day is mostly cloudy, and the second mostly sunny. On the sunny day, the ceiling cavity of the tile roofed house rises to about 20 degrees above the outside temperature. From my observations, this is fairly consistent with the sunny-day performance of this roof in summer.
The colorbond roof space stays pretty close to the outside temperature. This difference in performance is partly due to the colour, and partly the insulation under the sheets. I was interested in this result because it shows that there is no advantage in venting this roof for the sake of thermal performance. That will help keep the roof cleaner and the insulation lasting longer.
While there is a dramatic difference in the in-roof temperature, it doesn't translate to a huge economic imperative. By the time you have well-installed R4 batts on the ceiling, and good air-conditioning duct insulation, there's not a huge heat flow anyhow. I estimate there may be around a 1kW lower loading on a air-conditioner during the sunny time of the day.
Thanks for that.
Bet you're happy with the choice of a light coloured roof, I wish more people would choose them
Would be awesome if you had more measure, i.e. light coloured tile versus dark colorbond, with and without sarking... but still really interesting results.
I have a dark tile roof
Only choice that was available, but I did put sarking in.. so I hope that helps.
One John,
Thanks for this info.
It confirms my decision to have a surfmist roof with 75 mm foil backed roof blanket under on my build.
Would be interesting to compare white tile (Monier Vodka range or similar) with white colourbond.
I would bet that a white tile should be better.
Would be interesting to compare white tile (Monier Vodka range or similar) with white colourbond.
I would bet that a white tile should be better.
Probably not, as during summer it would release heat back in to the roof as it cools down... just like bricks store the heat for later release.
My roof is Surfmist colourbond roof.
Thanks for posting that onejohn. Interesting comparison.
How did you do the measuring ?
Stewie
Probably not, as during summer it would release heat back in to the roof as it cools down... just like bricks store the heat for later release.
My roof is Surfmist colourbond roof.
well tile should release the heat with some time lag (less lag than brick though), meaning this heat will be released evenly at night. However, colorbond will transmit absorbed heat straight to the air of the underroof space almost with no lag. So actually hard to say, yet intuition tells me white (not gray) tile should win. In both cases the white layer will keep warm from being emitted back during night.
Would be awesome if you had more measure, i.e. light coloured tile versus dark colorbond, with and without sarking... but still really interesting results.
I have a dark tile roof
Only choice that was available, but I did put sarking in.. so I hope that helps.
I have read one report that concluded that in Melbourne and further South, that the benefits of a dark roof in winter offset the disadvantages in summer. A dark roof does help in winter, but with the lower sun angle and fewer sunny days, it won't collect as much heat in winter. Then it's not so much the sunny days when you need heating anyhow. But still, dark does have some advantages.
How did you do the measuring ?
I logged one house with an Elitech RC-5 temperature logger. It costs around $20 and seems to work quite well logging data for several months. For the other one I used cheap wireless weather station transmitters and logged them to my PC using a USB TV tuner and the RTL433 software. It could be interesting to get a few of the Elitech loggers, and ask some neighbours with different roof types to put them up in their roofs, and then compare at the end of the season.
I'd be interested to see the difference between three light coloured roofs of the same type eg Colorbond surfmist - one without sarking, one with and the third with a decent blanket like you have used in your new house.
Stewie