Technical Comparison: Untreated Roof ~ vs ~ Heat Reflective Coating
The heat insulation industry refers to a roof coatings reflectivity as a ‘TSR’. (Total Solar Reflectivity). This has traditionally been dependent on the roof colour.
If one uses very light roof coating, around 50% of TSR can be achieved. A new bright white roof surface can originally reflect up to 65% TSR, and make you cooler.
Before long, such as normally within the first two years of the coatings life, it will begin to break down (The white substance that soon wipes off as the solvents and polyester break down*) and the roof soon becomes non reflective again, loosing up to 40% of its original TSR. (*Not so good for water collection either)
This roof although light or white will soon reflect only around 10 - 30%. So the balance of 70% of heat is absorbed into the roof structure for conduction to carry the heat into the building and its occupants.
So traditionally, light coloured roofs will keep you a little cooler, but only for a little while.
If this was a bare roof, or if it had been coated with a darker colour, it would loose so much TSR that it will be reflecting only 3 – 5 % and absorbing up 97% of radiant heat. Situations like this can result in the roofs surface temperature reaching around 90 degrees on a strong sunny day.
Many Australian buildings in this situation are continually running air conditioning units that are trying to combat the constant heat source coming from the roof. Even thermal (wool/Paper/AirCell) insulation in the ceiling will then heat up and hold the heat in the building for hours.
How Heat Reflective Insulating roof paint will keep you cooler ~
Using heat reflective roof coatings, you can achieve up to 90% reflectivity in white, and as much as 30% reflectivity from a dark black or charcoal coating. Different manufacturers TSR guarantees range from 10 to 15 years.
Here are some comparative examples of traditional colours TSR, compared to a reflective coating in the same colour. (TSR = Total Solar Reflectivity)
Colour Standard Roof Coating Heat Reflective Coating
White 15 - 20 % TSR (Worn) 85% TSR
Charcoal 6 % TSR 26 % TSR
Chocolate 7 % TSR 27 % TSR
Dark Green 7% TSR 35% TSR
Deep Blue 8 % TSR 30% TSR
There are a range of products available on the Australian market and each manufacturer uses their own specific and often confidential (trade secret) method of reflection.
Coatings vary in thickness from 40 microns (Similar to two coats of paint) to 450 microns, resulting in a reflective and thermal waterproof membrane. Again this is dependent on the manufacturer and the methods they develop. Often anticorrosive additives are included to result in complete roof preservation. Because the roof is kept at a more constant temperature, it no longer suffers thermal shock.
It pays to research the manufacturer carefully and scrutinize the warranty; as there are some imported paint additives available that use large ceramic sphreres that often looses up to 30% of its TSR within the first 12 months. Early technology using 'large' ceramic beads or spheres is one to be cautious of.
Many good quality Heat Reflective Coatings are Australian made, and some top performers have been manufactured here for 20 years. One manufacturer has been around for 28 years and exports 86% of its product to Dubai and China. Other Australian products are manufactured by licence in the United States of America. However Australia remains slow adopting our own technology despite our hot climate.
A high quality Heat Reflective Coating (in white) will cool roof steel down by up to 40 degrees, allowing the inside to cool down by up to 21 degrees in the worse situation.
Roof Ventilation - Whirlybirds have become an Australian icon, especially in Queensland; they claim to release hot air from your roof space and cool the home. Why allow the space to heat up in the beginning….and do they really work? See ‘EnviroTalk Urban Myth gets a run -
http://envirotalk.com.au/forum/index.php?showtopic=5419
Heat Reflective Coatings can also be used on walls, including a range of renders available in similar colours that will offer similar TSR’s to the roof and wall paint coatings.
There are also products available on the market for coating concrete paths and driveways. Even ground concrete convection can contribute to the ‘
Urban Island Heat Effect’
http://en.wikipedia.org/wiki/Urban_heat_island where residential areas can become 1 to 2 degrees hotter than the surrounding rural areas, because of the amount of building surface and concrete heating up and retaining the heat.
