This is especially for those of you whose house any ways a bit of doing up, or who plans to build a new house.
Do you know that painting your roof white or a light color alone could significantly reduce your cooling costs? Yes, this is because white reflects heat and hence the amount of heat entering your house is reduced!
What is a white roof?
A white roof is painted with solar reflective white coating and reflects up to 90% of sunlight (as opposed to traditional black roofs which reflect only 20%). A white roofs are a lot more than just white paint! White roofs’ benefits are measured partly according to the solar reflectance index, or SRI. A roof’s SRI is a measure of a surface’s ability to reflect solar heat. SRI measures reflectance (reflecting the sun’s rays) and thermal emittance (the roof’s ability to radiate absorbed heat). If you’ve ever worn a black t-shirt in the sun than you already understand that black’s reflectance is negligible and its emittance is zero. A white roof’s reflectance is as high as 90% and its emittance is 100%. Learn more from our friends at the Cool Roof Rating Council.
Why do we need white roofs?
The world is getting hotter, just in case you do not read newspapers!
In urban areas, the hotness is even more!
The Urban Heat Island effect is a measurable increase in ambient urban air temperatures resulting primarily from the replacement of vegetation with buildings, black surfaces like roofs and roads and other heat-absorbing infrastructure. Cities are full of these heat trapping black surfaces.
On a clear night, the temperature in a city with 1 million people or more can be up to 22°F hotter than nearby suburbs due to the heat island effect. Urban Heat Island effects include increased summer energy use, stress on the power grid, increased pollution, and health hazards such as asthma. Urban Heat Islands also contain hotspots (areas that are superheated due to population, environmental injustices or industrialization).
White roofs keep buildings cool and reduce energy use.
5–10% of summer electricity is used to compensate for the Urban Heat Island effect. We all end up spending bilions of dollars annually just to air condition buildings — In the US for instance, it is estimated that one-sixth of all electricity generated is used for air conditioning! White roofs can reduce summer energy use by 10–40%, saving money and preventing pollution. White roofs can reduce the total Urban Heat Island effect in an impacted city by 1° to 2° F – enough to lower peak energy demand for the utilities too.
White roofs help curb climate change.
White roofs help curb climate change. “…replacing non-reflective, dark roofing materials with white ones … (every 1000 square feet) would result in an equivalent CO2 offset of 10 metric tons (about $250) annually”.
White roofing prevents heat related warping and cracking extending the life of a roof. White roofing can reduce roofing waste added to landfills. Annually “roofing replacement generates 8 to 10 million tons of old roofing waste. Historically, about 95% (or 22 million cubic yards) … has ended up in landfills”.
What about white roofs in the winter?
In colder regions, you might think that a black roof would provide a winter heating benefit to building owners. However, there are several factors that make any potential heat gain relatively immaterial: The laws of physics dictate that hot air will always rise. Thus, any heat that is transferred to the interior of a building structure from the outside will remain at the top of the structure, providing minimal heat savings.In fact, in some areas, there is a greater than a six-hour difference between peak-summer and peak-winter sunlight, meaning there is less sunlight available to contribute to a building’s potential warming. Plus, the angle of the sun is less direct, which also helps to minimize warming potential.