Measuring of roof reflectivity

This is a great question, and one that has been on my mind as well. SRI is calculated using solar reflectance (albedo) and emissivity (emittance). If you have these two values, you can use a calculator like the one at http://www.arkema-inc.com/index.cfm?pag=986. If you don't have these values, you're in for some big excitement (so to speak).

Although I've never had to measure this myself, I have heard that it's a big pain -- and now I know why. I took a look at a slide show on this topic at the Lawrence Berkeley National Labs Cool Roofs website http://eetd.lbl.gov/HeatIsland/CoolRoofs/Overview/. This LBL group developed much of the leading research and research methods on this topic. To summarize, you need a combination of the following instrumentation, depending on the situation: UV-VIS-NIR Spectrometer with integrating sphere, a solar spectrum reflectometer, and a Fourier-Transform Infra-Red (FTIR) spectral emissometer and/or an emissometer. The protocols must comply with specific ASTM standards for each type of measurement.

If your project is local and presents a scientific question that might pique LBL interest, perhaps you should contact them for advice or assistance. (A note to other readers, Lauren is lucky to be practically in LBL's back yard.) Paul Berdahl is the primary contact for SRI info, see http://eetd.lbl.gov/HeatIsland/STAFF/.

Although I didn't see a specific discussion on the question of roof vs. hardscape measurement procedures, it makes sense that they would be the same.

Have any other readers undertaken these measurements themselves?

It may be more cost effective to send a sample to a lab, instead of bringing the equipment on-site. We researched this for a project where we were filling the cells of pervious pavers with gravel; we had manufacturer SRI values for the pavers themselves, but not the gravel. It ended up not being necessary because the USGBC reviewers accepted the paver value for 60% of the area (excluding the 40% voids filled with gravel), which put us over the 50% area threshold. The lab we received quotes from for testing was Atlas Material Testing in Phoenix, www.atlaswsg.com.

To clarify, projects using an existing roof must test the roofing material on site (or via lab sample) to comply with this credit? I am involved with an NC major renovation, and 50% of the roof is receiving a new coating with a high SRI value while the other 50% will be the original, unchanged white surface. Unfortunately we have no way of tracking down the manufacturer information of this original material, as we have no means of communicating with the past owners (the building was foreclosed on and sat vacant for a few years). I assume we cannot just choose a value from the table in the LEED reference manual? We must actually perform an SRI test on site?

Does anyone have any experience with this type of project?

Patty, that's correct, you have to perfom an SRI test onsite, or obtain a sample of the roof and send it to a lab.Either option may be difficult to pull off and I haven't heard stories of people doing this.