Cooling load & Heating load for Green Roofing
Your home and/or business is a container that should keep you safe from the outdoor elements of rain, snow and excessive amounts of heat and cold during the appropriate months. The indoor environment is greatly effected by temperature, humidity and breathable indoor air quality (known as IAQ). Your roofing system is simultaneously the most exposed portion of your home/business to the outdoors and plays a part in containing and managing much of your indoor environment So, the question arises: How can we create the best balance between elemental protection and indoor environmental control through your roof system? Here is where we address Cooling Load and Heating load.
Your roof acts as a transfer medium for heat into your home/business at all times of the year. This can be a good thing during the Winter months and a bad thing during the Summer months. And, here we are talking about physical comfort and the amount of energy it takes to cool or heat the living/work space to achieve that comfort. Latitude and direct exposure to the Sun plays a large part in this equation. Denver, Colorado, USA is our local benchmark.
Cooling Load
The amount of energy that is transferred as heat into your home/business is determined, to a large extent, by the Solar Reflectance index (SRI) values of the roof system. This is a measurement of the solar reflectance and solar gain through the visible and non-visible wavelengths of the Sun's light and energy on the roof surface (ref LEED-NC, version 2.2). The reflectivity of roofing varies greatly, depending mostly on the color of the surface and other factors such as the type of paint/coating, granule or chemical component of the surface. Emissivity, which is related to solar gain in how quickly the surface releases heat, is greatly determined by the substrate beneath or within the roof surface and the chemical composition involved. White and light pastel colors and coatings, galvalume steel substrates, some tile, poly-vinyl-chloride (PVC) and tri-polymer-olefin (TPO) all tend to have high solar reflectance ratings (SRI).
These concepts of the reflective and emissive properties of roofing material are well worth considering when installing steep and low slope roofing systems to keep out the weather and reduce the energy consumption that comes with extreme Cooling Load demand.
Heating Load
Though there are benefits to passive solar gain through a roof system in the colder months of the year, especially in more Northern latitudes, I believe there are better ways to use the Sun's warming energy that will not advance the damage and depreciation of the roofing structural medium.
Consider thermal solar systems for hot water, radiant floor and holding tank home heat. Also note passive solar gain through low E glass windows and skylights and concrete and stonewalls and tile and stone flooring. For a cost comparison between heating load and cooling load ask us about the Cool Roof Calculator.
Contact us at info@3rroofing.com