July 27 - August 8, 2010
How can I determine if my hospital building in Philadelphia can benefit financially from installation of a reflective roof coating on top of the current black roofing substrate on a flat surface?
tim barrett of barrett co. on
August 5, 2010:
You have some good info for calculations but you should also consider a green vegetated roof for a bigger bang for your buck. See
www.greenroofs.org for unbaised info
and good luck however you decide.
Tom Cahill of Polarhide on
August 3, 2010:
Figure out where Philadelphia stands on the number of cooling days vs. heating days at the Urban Heat Island website at Lawrence Berkeley National Labs. Run the website's calculator (easy to use) to determine your roof's likely per- formance if cool coated. That should start you on a reasonable ROI analysis.
With an abrupt change of roof color from black to white in Philadelphia, you should see savings of 25% on AC electrical demand on your hottest days, and in winter about 4% savings. Check your roof for standing water. There are 1,500 water-based cool-roof coatings that severely restrict warranties against standing water, a major cause of roof degradation.
Use cool-roof coatings that offer good standing-water warranties. Consider the maintenance implications of cool-roof coatings in your ROI analysis, since the cooling of the roof naturally reduces the main cause of leaks on any roof--solar heat.
Bear in mind unique aspects of hospital roofs where cool-roof coatings are concerned. You may not want to coat a roof below the level of windows in an attached building where the intense reflection from the roof comes through the windows into the patients' room or surgeries, etc., and also heats up the walls and windows of the taller building.
On balance you will benefit financially from a cool coating, but anticipate a 5-year or 8-year ROI in Philadelphia.
Joseph Schinner of Akzo Nobel Coatings Inc. on
August 3, 2010:
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You probably can't determine a positive benefit.
For a "tall" building, the roof area doesn't affect as much as a low, flat building due to the proportion of roof area and non-roof area (outside dimensions). The DOE has low slope roof calculations that theoretically determine a difference that can be transferred to energy costs, but in real life this could only be done by comparing the exact same summer/winter conditions before and after the re-roofing with reflective material. An institution with a thicker roof on a cement base, with insulation material-- even if it is only "fire-proofing" above ceiling and with airspace above ceiling tiles--might very well not show significant cost savings after the huge re-roofing costs.
The studies done in California by the state with DOE, etc. should be carefully consulted before deciding.
Reflective roof coatings
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