Message Board Thread - "Summer Time: Roof color for energy saving"

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Summer Time: Roof color for energy saving thermoimagen 3/17/2004
well, the Spring downhere at mexicali start to rise close to 100F, so the Summer surely will get the media of 120F at shadow ..

The most of domestic roof uses for rain protect (media is 5-10mm anually!!) green or red sand cartoon. i had calculate the emisivity for this materials and had found over 0.9 !! besides just few houses have wood roof, the most of houses the roof are from concrete (high emisivity value too over 0.95 dry)

The problem here at the city is the high cost for energy on summer time. most of the energy used is for air conditioners units.

There are tv spots where teach the citizen to save energy like keep doors and windows closed, using electronic lighting, the use of high energy freezer etc.

i had watch that the heat exchanche thru brick walls and block walls are huge!!

My first Question is:
Is there and material high reflectivity that avoid the heat up of roof and walls?..sometimes put a tree can works but we can not wait for the tree grow up!.

Insulation materials (like foam sheets) can works but how thick is enoug?.. is there any formula to get the minimum foam thick?..

i was thinking to use aluminum foil on the middle of my house roof but like zebra type.

any ideas to reduce the air conditioner on cycle will be apreciate.

Re:Summer Time: Roof color for energy saving IRJay 3/17/2004
I am in a "cooler" climate and we tend toward darker roofs for the energy absorbtion. SO conversely if you want a cooler roof go towards a lighter color if not white. A reflective barrier would work well also but if the building does get warm the barrier will prevent some cooling as the surface no longer radiants. Remember that heat absorbtion is not just in the infrared spectrum. Exmaple is the reflective strips put in car windows to keep cars cool. These don't reflect much infrared as it can't pass through the glass anyway. So the idea is to keep radiated sun energy from being absorbed and then insulating the structure to prevent the absorbed energy from conducting into the dwelling.

Another answer lies in a reflective barrier on the inside of the walls which will reflect the cooled air back into the dwelling. Checkout for some ideas there.
Re:Summer Time: Roof color for energy saving Gary Orlove 3/17/2004
From a practical viewpoint, as IRJay says, the most cost effective and simple solution is to paint your roofs white.

White will reflect much of the visible light from the sun during the day and yet has a high emissivity so you can radiate heat away during clear nights; just what you want for a hot, dry climate.

For these climates, a high mass (heavy) construction works well too. I have been in the Alamo in Texas during a summer day and it is remarkably cool and comfortable inside without air conditioning, due to the thermal capacitance effects of the thick walls and roof.

Add insulation into the mix and you should be comfortable with very low energy costs.

Gary Orlove
Infrared Training Center
Re:Summer Time: Roof color for energy saving Doctir bob 3/17/2004
Reflective paints or coatings on roofs can create more heating, rather than less. Here's how: Metals have fairly good absorption in the solar spectrum for visible waveband, something like 0.6. But they are very poor emitters in the IR band. So, metals will absorb solar radiation, but not re-emit it. So, they can get very hot. Anyone who has tried walking barefoot on a metal roof in the summertime knows this. It is much better to use a very white paint, such as Titanium white. This reflects solar radiation very well, and also emits quite well in the infrared. For areas not directly in the sunlight, metals can be good reflective thermal barriers.
Re:Summer Time: Roof color for energy saving thermoimagen 3/17/2004
thanks Guys, I will paint white my roof.
Cool Roof programs and best materials Scott Willits 3/18/2004
Actually, there are specialized roof coatings manufactured to specifications that deliver exactly the benefits you are seeking. I know Henry's makes one such compound. From what I understand, they strike a balance between emissivity and reflectivity so that you not only reflect the majority of insolation, but allow for heat transmission through the roof to the sky when ambient conditions allow. The State of California has even provided a credit for application of Cool Roof treatments under its Title 24 Building Energy Code.

Here's one website with some great information:

Or just do a Google search for "Cool Roof" and you'll come up with more than you could ever read on the subject.

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