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Old 07-22-2011, 07:43 PM   #1
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tarp a flat roof for cooling/insulation?

I have a flat roof one story house and have been trying to come up with a way to insulate the roof to regulate the temps indoors. I have heard of 'cool roofs' and looked into painting but also wondered if putting a white tarp, maybe even an insulated tarp, would work better and cost less? the house is 1100 sq ft and i was quoted $800 to paint the roof white which seems pricey to me.

If i did put a tarp up there and secured it around the edge so it didn't fly away, would it be alright? or is there a possibility of water buildup or damage to the roof?
i assume that having a tarp over the existing roof might actually help protect it if installed correctly, but i don't know...
i need a solution for this old oven of a house! help!


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Old 07-23-2011, 08:49 AM   #2
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I've never seen a white tarp personally. Not that they don't exist, but you'll have to hunt around for one. There is also a useful life expectancy of a tarp and it's not more than a year. It's goign to get pretty beat up by the sun (even if it is white) and wind. In theory, it could work for a short time. An upside down roof, IRMA I think it is called, is a roof with the insulation over the membrane. You can install EPS, which is ok to get wet, over the existing roof membrane, then install your tarp or some kind of ballast to keep the EPS in place. Keep in mind the EPS is UV sensative and you would definetly want to keep it covered or it won't last a few years.

My opinion, while your idea is possible, I think it is an exercise in futility and not worth the extra money. I don't know the size of your hosue, but $800 seems like a deal if the person installing the "paint" is licensed and insured and using a good quality elastomeric roof coating, not PAINT.

The permanent fix is 3 part. Reflectivity to block as much heat as possible from absorbing into your building, insulation to block any heat that does absorb from transferring to the interior, and possibly ventilation depending if your roof is a warm deck or cold deck design. I presume the roof is a cold deck design since it is residential and fairly common on wood frame structures. What "cold deck" means is that the roof is not insulated, but instead, the ceiling is insulated. There then should be some kind of ventilation installed as part of the system in the cold deck design.

For a point of refrence a flat roof with a warm deck would have no insulation in the ceiling, but would instead have the insulation above the wood substrate and below the roof membrane. There then would NOT be ventilation in a warm deck design.

What ever your house is currently designed, my advice would be to honor the original design and not change it. Meaning if it's a cold deck, keep it a cold deck, if it is a warm deck keep it a warm deck. However you can do something to improve the overall effectiveness. You can achieve a much higher R value in most cases by insulating the ceiling. I install both on a regular basis and have found that on a 1,500 sq ft, I can install r 30 in the ceiling for less than I can install r 9 on the roof. For comparison purposes to install r 30 on the roof using Poly Iso Cyanurate insulation you would beed 5" thick and the cost would be nearly triple that of fiberglass installed in the ceiling. furthermore to install 5" thick of insulation on your roof may mean changing alot about your roof such as the height of pipes, curbs, etc...

You can learn more about Ice damming and Attic ventilation explained. While this article was not written specific to flat roofs, actually it was written specific to steep slope roofs, the article will still give you good information regarding how ventilation and insulation work in conjunction. I would also suggest reading more about your Flat Roofing Options.


-Grumpy http://www.illinoisroofinspections.com
The information found in this post is not to be considered legal advice. The author of this post takes no responsibility for any losses that occur. Use at your own risk.
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