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Old 05-19-2008, 05:46 PM   #1
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Cover roof to lower temperature?


Would a cover to shade a flat roof significantly decrease the temperature inside?

My sister bought a two-story duplex last year. It was built in 1925 and was neglected for many years but it's still standing.

It was quite hot for the SF Bay Area last week (temps in the 90s) and the upper unit was an oven. The only insulation is in the attic crawlspace, which was blown in this past winter after the electric was upgraded. There are vents on two sides of the attic. The windows are old double sash single pane. Basically, an insulation nightmare.

My sister's repair budget is shot and we're looking for a creative solution to the heat issue. The roof is relatively new torch-down with a reflective silver coating. It's in great shape.

What if we covered the roof with something like a tarp? Perhaps we could build a frame so the tarp was, say, a foot above the parapets? The building has wood siding so it'd be easy to fasten to the sides. We'd have to figure out a way to minimize wind uplift but that seems doable.

Would this make any real difference? Or would the ambient temperature combined with the lack of insulation raise the temp anyway? It seems like shading the roof would make some difference, but I don't really know.

Thanks for any help on this.

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Old 05-19-2008, 08:11 PM   #2
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Cover roof to lower temperature?


The tarp would burn out rapidly and also be ripped to shreds after even limited exposure to the West Coast UV rays and coastal winds.

There are way more than one situation creating the oven effect in the upper floor. The reflective coating is already doing as much as it can to keep the roof surface temperatures down and reducing the heat transferance.

Without getting into expensive remedies, your options seem limited. Possibly getting a PUF, Poly-Urethane Foam roof, which is in and of itself, an insulating system, along with a reflective surface coating would be one plan of attack.

Let me know where else your energy deficiencies are coming from for a possible better answer.

Do your utility companys come out and do a free energy analysis and provide suggestions on decreasing the heat island factor in your buildings?

Ed

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Old 05-19-2008, 08:37 PM   #3
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Cover roof to lower temperature?


Thank you for the reply, Ed.

The tarp would burn out rapidly and also be ripped to shreds after even limited exposure to the West Coast UV rays and coastal winds.

I suspect you're right. I'm wondering if it might hold up for a month or so. This is Oakland where there's usually no more than 3-4 weeks in summer where it's 90+ degrees.

There are way more than one situation creating the oven effect in the upper floor. The reflective coating is already doing as much as it can to keep the roof surface temperatures down and reducing the heat transferance.

Makes sense. I think the heat is penetrating right through the uninsulated walls and single pane windows as well as the roof. Intuitively it seems that a cover would make some, however slight, difference- the roof would be in the shade- but I think I'm grasping for straws.

Without getting into expensive remedies, your options seem limited. Possibly getting a PUF, Poly-Urethane Foam roof, which is in and of itself, an insulating system, along with a reflective surface coating would be one plan of attack.

I appreciate the suggestion. This is financially impossible now but maybe down the road.

Let me know where else your energy deficiencies are coming from for a possible better answer.

Well I'm thinking the deficiencies run the gamut- the whole place is uninsulated except the attic. I can't think of any area that is energy efficient.

Do your utility companys come out and do a free energy analysis and provide suggestions on decreasing the heat island factor in your buildings?

Good idea-- I'll look into it. I also spoke with a contractor who said that until the windows are replaced and insulation is blown into the walls there's not much to be done except air conditioners.

Thanks very much for the feedback.
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Old 05-19-2008, 08:44 PM   #4
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Cover roof to lower temperature?


For the cheap quick fix on the windows, try one of those stick on films that would reflect the radiance.

Also, keep the blinds and curtains closed when the sun is shining directly towards them. It helps out a lot.

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Old 05-19-2008, 09:00 PM   #5
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Thanks again, Ed. This is very helpful and much appreciated.
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Old 05-19-2008, 09:08 PM   #6
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Read up on the product a little bit first, with some secrets the "film" manufacturers don't blurt out.

http://www.chiefengineer.org/content...ntent/1586.htm

Now, here is a bit more info on it for its benefits and what to watch out for.

http://www.powerhousetv.com/stellent...bu_000524.hcsp

Ed
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Old 05-20-2008, 10:18 AM   #7
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Cover roof to lower temperature?


Great links-- thanks Ed. I remember when a friend had film installed she talked to several companies and there were only a couple of products that gave good visibility and reflectiveness. And they were pricey, probably similar to what was quoted on the second link ($40-60 per window).

Combined with blinds they seemed to be quite effective, and they were nearly invisible and non-darkening-- if you didn't know they were there you couldn't tell.

This is definitely a possible option. Much appreciated.
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Old 05-20-2008, 11:57 AM   #8
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Cover roof to lower temperature?


For about a buck a foot (in Chicagoland) you could get a white acrylic coating applied that will reflect up to 70% UV at two gallons per square. This could help dramatically.
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Old 05-20-2008, 08:17 PM   #9
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Hi AaronB,

Thanks for the suggestion. The roof has a silver reflective coating but I don't know what the UV rating is. I'll check around and see what's available.

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