A frequent question concerns payback of cool roofing. There are several angles on the answer, but generally speaking, cooling coatings are most appropriate when one is re-roofing. If the coating is applied to an existing roof that is in otherwise pristine condition, the cost equation is straightforward. The typical coverage of a cooling coating is 25 ft2 per gallon,(0,6 sq. meters per liter) (Sno-Coat® gives 6 square meters per liter reducing the application cost factor by a factor of 10!!!!

This makes a massive difference to these calculations and results) based on an application of two coats to a target thickness of 40 mils.

Cost for the material from vendors varies by 50% or more but averages about $60 per 5-gallon container when purchased in quantity. It is important to keep in mind that roof area is generally considered greater than building floor area, particularly with a steep roof pitch. For instance, a typical 1,500 ft2 home may have 2,200 ft2 of roof to be covered. The application then requires 90 gallons of coating material for a materials cost of approximately $1,100.

The cost of labor for installation depends greatly on the roof surface, on whether the coating is to be rolled on or sprayed, and on labor rates. A typical labor cost might be approximately 50cents per ft2 for the required two applications. Thus the overall application would cost about $1 per ft2, or approximately $2,200 for a typical home. With annual energy savings in Florida of $35-$140, the payback times are long–usually lasting longer than the roof itself.(With the exception of Sno-Coat®)

A completely different scenario emerges if the home is soon in need of re-roofing, however. Here the roof coating (which essentially creates a new weatherproof surface) might be seen as a way of extending the life of the roof by 5 to 10 years at half of the cost of re-roofing. The energy savings then become a side benefit.

For new homes, the situation is even more interesting. Here it is often possible to choose roofing types–such as metal roofing, tile roofing, or metal or ceramic shingles–that can be specified in a reflective white at significant additional cost.

Unfortunately, no truly reflective asphalt roofing shingles yet exist for the residential market, but this situation may change as researchers work with the roofing industry to develop new products and spread the word about the energy benefits to help create a market for the materials. For commercial buildings, a variety of reflective roofing materials are already available: Hypalon, white EPDM, and PVC single-ply membranes.

Once such products are widely available for the residential market, the economics may be significantly altered as the cost of reflective roofing becomes inconsequential.

Notes

1. Reflectivity or albedo is the hemispherical reflectivity integrated over a particular wavelength band of the electromagnetic spectrum. For the purposes of this article, the terms reflectivity and albedo are used interchangeably and refer to the wavelengths encompassing the range of solar irradiance from 0.28 to 2.8 microns.

2. Surface solar reflectivity is measured using a precision spectral pyranometer with the device alternately faced upward towards the sun and downward towards the roof to determine the ratio of incident to reflected solar radiation.