Air conditioning cools your home dramatically, but it's expensive to install and run. Plus, it's not exactly the prettiest thing in your yard. So, for these green times, we revisited the oldest house-cooling trick in the book, white paint, but with a modern twist: UV rejecting additives.
You can buy powdered additives like Insuladd to mix into any house paint and, supposedly, give it the ability to reflect UV while also insulating your home. You can also buy preformulated heat-rejecting paint like Rainguard Cool Coat that makes no claims as to insulating qualities, just heat rejection. The idea is the same: Bounce back the sun's UV rays better than white paint alone to prevent the underlying walls from heating up and transferring that heat to the interior of your home.
To compare all three, we painted identical siding boards with the coatings and placed them in full afternoon sun on a 75-degree F (24 C) day -- not exactly a scorcher, but often the best we can muster along San Francisco Bay.
The results were both encouraging and disappointing: Regular white paint allowed a board to sit in the sun yet show no measurable heat absorption, reading just about the same as the ambient temperature. But, according to our laser temperature gun, the UV blocking paints didn't really keep a board any cooler. Similar results were recorded on the backs of the boards where heat transfer was measured.
To show how remarkable white paint is, a brown stucco wall under the same conditions registered nearly 25 degrees F warmer than the same wall painted white, albeit with one of our white UV paints. Bottom line: It seems like any white paint is amazing at keeping your house cool.
We only tested white paints and perhaps UV-blocking technology makes more of a difference when used with darker colors that need more help rejecting heat. But if you want to cool your home with the easiest, most affordable stroke of a brush, paint it white and you may not have to sweat any fancy tech.
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