Solar Reflectance of High Profile Roofing Materials

An overview of CRRC research and activities

Technical Committee MeetingNovember 17, 2008

Technical Committee Meeting November 2008

The Short Story• Physics shows that profile can decrease the solar

reflectance of roofing products• Various studies have attempted to assess the

significance of the impact and produced conflicting results

• The CRRC has established a policy for profiled metal roofing products

• The Tile Roofing Institute has conducted their own study and is asking the CRRC to establish a policy for profiled tile roofing products

Technical Committee Meeting November 2008

The Physics of Profile and Reflectance

• When solar irradience strikes an opaque surface, it is either reflected or absorbed

• The angle at which the irradience strikes the surface affects the degree of reflection and absorption

Technical Committee Meeting November 2008

What is a Profiled Roofing Product?

• Proposed definition: A profiled roofing product is one that has significant height changes within a relatively small area (1 or more inches of height change per 1-2 square feet)

• Roofing product profile does not account for the profile of the actual roof

Technical Committee Meeting November 2008

A Shield vs. An Echo Chamber

• For flat roofing materials, reflected solar irradience cannot strike again

• For profiled roofing products, some reflected irradience beams may intersect the roofing surface again, providing additional opportunities for absorption

Technical Committee Meeting November 2008

Tilt Matters

• A flat roofing material presents a uniform angle of tilt to the sun's energy

• Profiled roofing materials may present many different angles of tilt for a given roof structure

Technical Committee Meeting November 2008

How Much Impact?

• Physics dictates that profile will affect solar reflectance-the question is, how much?

• Does profile make a significant difference to the solar reflectance of roofing products?

• What is a significant difference?• Are certain products or colors more affected?• Can we quantify and predict the impact?

Technical Committee Meeting November 2008

Findings: ORNL

• Mr. Desjarlais of ORNL compared stone coated metal shingles of two different colors and three different form factors (flat, tile, shake).

• Data from this study clearly indicates that as profile increases, the solar reflectance of the shingle assembly decreases.

• The impact was found to be greater for the light-colored samples.

Technical Committee Meeting November 2008

Findings: CRRC and LBNL

• LBNL and the CRRC conducted a study that compared measurements made with E903 and E1918

• For all the tile products measured, the average solar reflectance of the flat coupon was higher than the solar reflectance of the profiled tile assembly

• Although the flat coupons used with E903 were of the same nominal material, they did not come directly from the tiles measured with E1918

Technical Committee Meeting November 2008

Findings: CMRC

• CMRC compared the flat and profiled solar reflectance of three different types of metal roofing product. All tests were conducted using E1918.

• For each profile type, measurements were taken for three or four different colors.

• All colors and profile types showed some reduction in solar reflectance due to profile, but only the Regal White standing seam product showed a reduction of more than 5 points.

• Some of the measurements show an increase in solar reflectance for the profiled products. This runs counter to the physics underlying the study and introduces the question of error in the E1918 test procedure.

Technical Committee Meeting November 2008

What's Happening Now?

•The CRRC has decided to allow most profiled metal roofing products to be rated using flat samples•TRI is conducting their own study on the impact of profile on the solar reflectance of tile products•The CRRC will need to formulate a policy for profiled tile products so that these items can be rated

Questions?