Cool Roof
Last Post 12 Dec 2018 08:30 PM by 1201. 26 Replies.
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drlebelUser is Offline
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26 Oct 2012 06:47 PM
Wondering if the cool shingles by certainteed and timberline are worth the cost or if the cost should be rolled into insulation. Live in Memphis Zone 3 with 120 squares or roof. Anybody have experience with them? And are radiant barriers as effective as everybody thinks they are or should that cost also be rolled into insulation. Thanks
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26 Oct 2012 09:07 PM
Posted By drlebel on 26 Oct 2012 06:47 PM
Wondering if the cool shingles by certainteed and timberline are worth the cost or if the cost should be rolled into insulation. Live in Memphis Zone 3 with 120 squares or roof. Anybody have experience with them? And are radiant barriers as effective as everybody thinks they are or should that cost also be rolled into insulation. Thanks


I don't think folks replace a servicable roof with a cool roof and try to justify the cost based on energy savings. If the roof needs replacing anyway, then a cool roof using shingles should be about the same cost as a roof with standard shingles, and then the energy savings can be significant.
Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
LbearUser is Offline
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27 Oct 2012 12:08 AM
Lee Dodge is correct. If you need a new roof go with a cool roof. If you don't need a roof, paying for a cool roof is not worth the potential saved energy costs. I got quoted $1.65 per square foot for a standing seam metal cool roof. This does NOT include underlayment or install costs, just the metal material.

Cool roofs in southwest desert climates are an excellent choice during a new build. They have done studies that when outdoor temps are 90F, the roof surface temps can see 160F on a asphalt roof, a 70 degree increase. With a cool roof, that same roof could see only a 10 degree increase over the ambient 90F air temperature, or 100F degrees.




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27 Oct 2012 12:08 PM
Be careful with cool roof claims - most of them apply only to flat roofs. With a sloped roof, it is far less important.
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28 Oct 2012 01:52 AM
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28 Oct 2012 01:55 AM
Posted By jonr on 27 Oct 2012 12:08 PM
Be careful with cool roof claims - most of them apply only to flat roofs. With a sloped roof, it is far less important.

The SRI number on a cool roof applies to both flat and pitched roofs. I don't understand what you mean by it being far less important with a sloped roof? The number doesn't change with roof pitch, it can only change with age.
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28 Oct 2012 08:06 PM
But the btu gained is the important figure and it is far less on a sloped roof.
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28 Oct 2012 10:05 PM
Posted By jonr on 28 Oct 2012 08:06 PM
But the btu gained is the important figure and it is far less on a sloped roof.

A lot depends on the homes positioning, time of year, and climate. If you have a 4:12 pitched roof area that faces predominately south and west, it will get blasted by the sun during spring equinox, summer solstice, and fall equinox. If that home is in Phoenix Arizona or Las Vegas Nevada, the roof will get baked all year long, even during winter solstice.

The studies show that a roof, both low and steep sloped applications, benefit from cool roofs. All but the most extreme Zone 6+ climates saw positive gains from cool roofs.
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29 Oct 2012 10:17 AM
The large difference between flat and sloped is mostly caused by convection.
Dana1User is Offline
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30 Oct 2012 04:14 PM
What jonr said- the peak temps of pitched roofing is limited by the combined convection & radiation cooling of the shingles, whereas with low-slope roof it's all about radiational cooling, since the buoancy of the heated films of air don't develop a sustained flow on flat roofs the way they do on pitched roofs. That's why under CA Title 24 code the SRI requiremnets are different for roofs at 2:12 pitch or lower than they are on steeper roofs.

Radiant barrier is roughly as effective, and a suitable substituted under CA Title 24 2008. But if you have the room for more insulation and you're at code-min or less, you're almost ALWAYS better off spending the money on deeper insulation (up to about R50-R60 in climate zone 3). Using a denser infrared-opaque blown insulation like cellulose or rock wool is somewhat more effective than low density fiberglass or any type of batts.

From a cost/benefit point of view, cool roofs generally cost more in heating energy than they save in cooling costs in US climate zones 5 & up for sloped roofs, but in zone 3 & lower it's a net win on annualized energy use. Of course the assumptions on cooling & heating fuels & efficiencies can skew that by quite a bit. If your shingles have a decade of life left in them it's not worth re-shingling with cool-roof shingles, but it's worth going there when you really need to re-shingle, whether you have R50 cellulose up there or not.
drlebelUser is Offline
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31 Oct 2012 01:11 PM
Thanks. It's a new roof but my contractor is telling me the cool roof is about 15% more. About 2000 for 120 squares. Is that still worth the investment because tht could buy a lot of insulation or a radiant barrier?
Dana1User is Offline
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31 Oct 2012 03:21 PM
120 squares!?! That's some roof! (A little weekend getaway cabin, mayhaps? :-) )

For $2KUSD you'd be better off going with more insulation, if you have the depth for it. (I'm surprised that it's that much of a price difference!) I'd be surprised if you could get 120 squares of radiant barrier installed for anything like $2000. But $2000 would buy you another ~R15 of cellulose, taking you from a code-min R30 up to at least IRC 2012 levels (R38) or better.
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31 Oct 2012 07:18 PM
Posted By Dana1 on 31 Oct 2012 03:21 PM
taking you from a code-min R30 up to at least IRC 2012 levels (R38) or better.

I thought 2012 IRC is R48 minimum for the roof in zones 3 and higher.
drlebelUser is Offline
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01 Nov 2012 05:11 PM
lol...Definitely not a cabin...will be the last home i build and live in I hope. Gotta fit the mound of children my wife keeps adopting. My brother is the architect and loves some roof lines. Okay so insulation is better. Should I rely soley on soffit and ridge venting or invest in powered or solar attic fans. Thanks for the replies.
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01 Nov 2012 07:16 PM
Posted By drlebel on 01 Nov 2012 05:11 PM
...snip...
Should I rely soley on soffit and ridge venting or invest in powered or solar attic fans.


Current wisdom it to avoid attic fans, whether solar powered or not:
http://www.greenbuildingadvisor.com/blogs/dept/musings/fans-attic-do-they-help-or-do-they-hurt
Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
jonrUser is Offline
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01 Nov 2012 08:55 PM
More accurately, avoid attic fan configurations that depressurize the attic. While most configurations do that, they don't have to and done right, could actually reduce home in/ex filtration, improve air quality and reduce moisture problems. Shame on the "experts" that don't understand that.
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01 Nov 2012 09:09 PM
Posted By drlebel on 01 Nov 2012 05:11 PM
  Should I rely soley on soffit and ridge venting or invest in powered or solar attic fans. Thanks for the replies.

At the risk of oversimplifying, whole-house fans are good. Powered attic ventilators are bad.

That is according to the article. IMO, attic fans are a scam, especially out in the Phoenix area. They push powered attic fans like crack out here. Studies show ZERO reduction in cooling costs and they have actually been shown to cost the homeowners more money because they draw electricity being on 24 hours a day.


drlebelUser is Offline
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02 Nov 2012 09:10 AM
Great info. Its staggering how much you think you know by assumption and how much is just flat out wrong.
Thanks again.
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02 Nov 2012 12:36 PM
Posted By Lbear on 31 Oct 2012 07:18 PM
Posted By Dana1 on 31 Oct 2012 03:21 PM
taking you from a code-min R30 up to at least IRC 2012 levels (R38) or better.

I thought 2012 IRC is R48 minimum for the roof in zones 3 and higher.

TN has not adopted IRC 2012 (or even IRC 2006), but for zone 3 the  IRC 2012 specifies R38 min, up from R30 (which meets current code in TN.)  R49 is now called out for zone 4, but not zone 3.
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02 Nov 2012 08:46 PM
Posted By Dana1 on 02 Nov 2012 12:36 PM

TN has not adopted IRC 2012 (or even IRC 2006), but for zone 3 the  IRC 2012 specifies R38 min, up from R30 (which meets current code in TN.)  R49 is now called out for zone 4, but not zone 3.
Wow, TN is really holding out if they don't even recognize the 2006 IRC. Out here they will implement the 2012 IRC sometime in 2013. They will amend the fire codes but will hold to the energy codes.

Would it be fair to say that Zones 1 - 3 make up about 20% of the entire USA while Zones 4-7 make up the remaining 80%?
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