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BUR? nd 7/2/2010
I am going to be conducting a survey on a BUR with Sika, Sarnafil S327 Energy Smart Roof Membrane white in color. I am concerned about the reflectivity of this surface not allowing me to see anomolies in the BUR. Any suggestions would help.


 
Re:BUR? jvoitl 7/2/2010
You won't need to know exact temperatures anyway but if your concerned get a roll of Scotch 33 electrical tape and measure the emissivity.
 
Re:BUR? jvoitl 7/2/2010
You won't need to know exact temperatures anyway but if your concerned get a roll of Scotch 33 electrical tape and measure the emissivity.
 
Re:BUR? ron lucier 7/6/2010
nd wrote:
ing to be conducting a survey on a BUR with Sika, Sarnafil S327 Energy Smart Roof Membrane white in color. I am concerned about the reflectivity of this surface not allowing me to see anomolies in the BUR. Any suggestions would help.


You didn't state what camera you are using but if it is a long-wave you should have no problem.

Most people get confused by the term "cool roof" as the manufacturer specifies high emissivity and high reflectance. This appears to be in conflict with the e + r = 1.00 for opaque surfaces that we teach.

Looking at Sarnafil's data sheet they specify solar reflectance at 0.83 and emissivity at 0.90 Unfortunately they don't specify the wavelength for either. Take a look at Planck's equation. Most of the heat of the Sun is in the very short wave-lengths - exactly where the roof is reflective. This also implies that the roof will be very emissive in the long-wave and they specify an emissivity of 0.90 So the roof is both highly reflective and highly emissive and there is no conflict as they are referring to two different parts of the electromagnetic spectrum.

A while back this issue came up and I did some simple Planck calculations and found that the Sun is about 10,000 times stronger at 4 micrometers than at 10 micrometers, both in the middle of the two common detector spectal ranges. Therefore the goal of a cool roof would be to have high reflectivity where all the energy is - the Sarnafil material is designed this way.

Refer to ASTM C1153, the standard for roof inspections. Best time to start a roof is right around sundown and the standard will give you guidance on minimum weather conditions.

Upload some images once you are finished. Goo luck!
 


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