In a recent study, Lawrence Berkeley National Laboratory (LBNL) analyzed commercial facilities and documented a decrease in roof temperatures and in energy use with a range of heat island mitigation efforts. A separate analysis of Florida Power and Light’s summertime peak load revealed an 82 MW or 1% increase in utility load for each 1°C (1.8°F) outdoor temperature rise (Parker 1988). If the rise in peak load means greater fossil-fueled based power production, the result is increased CO2 output. Additional information on how roofing composition affects temperature can be found in the residential section. Click here learn more about residential roofing.

Urban heat islands are also impacted by dark, heat absorbing pavement materials. Dark materials absorb more heat from the sun. Anyone who has stepped onto a parking lot or asphalt road in Texas knows it is considerably hotter there than under a large oak tree.

According to LBNL’s Urban Heat Island Group, black surfaces in the sun can become up to 70°F (40°C) hotter than the most reflective white surfaces. Roads and parking lots are frequently paved with black asphalt concrete (commonly called "asphalt") and other dark materials that absorb most of the sunlight that falls upon them. The energy of the sunlight is converted into thermal energy and pavements get hot, heating the air around them and contributing greatly to the heat island effect.

In urban regions, commercial facilities would have cooler summers if they began using light-colored and reflective materials for paving new roads, parking lots and resurfacing old ones as the need arose, installing "cool roofs" where applicable along with maintaining a tree canopy.

In Texas, two large commercial facilities have recently installed cool roofs. In 2002, the City of San Antonio’s City Public Service installed a "cool roof" on its new Northside Customer Service Facility. Trees on-site were protected during construction and additional trees were planted. The service center also used a light-colored parking pavement.

A large 100,000 square foot retail store in Austin, Texas replaced an original black rubber membrane with a white thermoplastic resulting in a decrease in the average maximum roof surface temperature from 168º to 126º. Total A/C annual abated energy demand expenditures were estimated to be $7,200. Based on cost data provided by the building manager, the payback is instantaneous with negligible incremental combined labor and material costs. (1) In the Houston metropolitan region, "cool roofs" have been widely installed from the HEB grocery chain to city facilities to local school districts.

Notes:

  1. This code presents equipment and installation standards in Chapter 13-8-500 of the Land Development Code, Article VII. Main code requirements: unit must have double wall heat exchangers, a glycol loop with circulating pump, and plans for retrofits must be stamped by structural engineer showing enhanced roof capacity.