Roofs

Roofs can lose and gain significant amounts of heat. The reflectance, emissivity, and insulation all are important components to consider in order to minimize these energy losses. If your rooftop is leaking, damaged, or excessively heating up in the summer time, it is time to consider a rooftop replacement.  

Emissivity and Reflectivity of Roof Materials

An important rooftop specification to consider during a new build or when renovating is the emissivity and reflectivity of your roof. Emissivity refers to a material's ability to release absorbed heat. Reflectivity refers to a materials ability to reflect radiation coming from the sun. Professionals generally use a number between 0 and 1, or 0% to 100% to express emittance and reflectance. Both emissivity and reflectivity play a crucial role in keeping a roof cool.

A composite rating system known as the solar reflectance index (SRI) considers both emissivity and reflectivity of materials and rooftop colors. The SRI is calculated using the reflectance and emissivity values given in ASTM E 1980. To meet LEED requirements, roofing materials must have an SRI greater than 29 for steep slopes (>2:12 – 2 foot rise for every 12 foot horizontal) and an SRI value greater than 78 for lower sloped roofing.

Roof Insulation

Roofs tend to lose more energy when compared to other exterior components of a home. For this reason, roof insulation typically has a higher R-value than insulated floors and walls. For the  R-value of roof insulation please check your local building code (find reference). For reference you can also visit ENERGY STAR®'s Website.

Tips:
  • Avoid insulating too close to recessed lighting fixtures (3" minimum unless otherwise stated on the fixture)
  • Avoid blocking ventilation vents
  • Avoid insulating too close to flue piping (3" minimum)
  • Avoid using faced insulation around any hot areas
  • Don't leave gaps between insulation! Gaps mean energy losses.

Roof Alternatives

Metal roofing

has gained popularity in recent years. Metal roofing is a lightweight, energy efficient, and sustainable alternative to traditional shingle roofing. Though more durable and efficient, the initial investment for a metal roof is typically higher than that of traditional shingles, but depending on the metal used this investment may pay itself off because of the lower maintenance requirements, lower energy costs, and longer lifespan.                                                                                    Image source: myhomecomfortcheckup.com

green roof

incorporates living plant system on top of them. Green roofs typically consist of a high quality water proofing and root repellant system, a drainage system, filter cloth, and a lightweight growing medium below the plants, therefore they have high initial costs. Benefits of green roofs include improved aesthetics, waste diversion, storm-water management, improved air quality, energy efficiency, and noise reduction.                                                                          Image source: www.wbdg.org

Resources

 

  1. "Cool Roof Calculator" by the Department of Energy - Estimates Cooling and Heating Savings for Flat Roofs with Non-Black Surfaces
  2. "Solar Reflectivity ( R ) & Solar Reflectance Index (SRI) by Color" by Dean Steel Buildings - Reflectance and Solar Reflectance Index of different colored materials calculated according to ASTM E 1980 used for compliance with LEED requirements.
  3. "Cool Roofs and Emissivity" by ENERGY STAR® - Great resource for learning about roof emissivity and how it relates to energy efficiency in your home.
  4. "Recommended Home Insulation R-Values" from ENERGY STAR® - Recommended insulation levels for retrofitting existing wood-framed buildings
  5. "Insulation" by Department of Energy - Learn how much insulation is needed for attics and roofs based on your location and rooftop type.
  6. Green Roofs for Healthy Cities North America (GRHC) - A not-for-profit 501(c) association working to promote green roof implementation.