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ICF869
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Posts:3
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| 07/07/2000 10:55 PM |
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Question form someone who is new to SIPS:
How do you deal with the problem of heat buildup on a SIPS roof? Since there is no ventilation through the panel, does the roof surface get too hot for conventional asphalt shingles? What measures do you have to take to make sure this isn't a problem?
Does the solution vary by climate? For example, do you need to do extra things in the deserts of the Southwest or the warm, humid climate of Florida?
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Steve Andrews
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Basic Member
Posts:334
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| 07/08/2000 6:10 PM |
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SIP roofs don't appear to be too hot for conventional asphalt shingles. However, good data, documentation and reviews on the subject of shingle life over unvented roofs (SIPs and others) are in somewhat short supply. Results from lengthy and carefully monitored studies are still a few years away. That said, here's some food for thought.
On the good-news side, I've talked with two home builders who have seen their original asphalt shingled roofs last 25 years over SIP panels. And Bill Rose, a research architect, reported last year that in identical 10-year-old roofing samples above SIPs and an unvented roof on the same test roof slope angle, he could see no significant difference between the two sample sets of shingles. Finally, at least one shingle manufacturer--Elk Corporation--stands by their warranty when their product is placed over SIPS.
On the bad news side, Certainteed decreased the life of its warranty (to 10 years, down from 20 to 30 years) when its shingle products are placed over unvented roofs. And in 1996, the Asphalt Roofing Manufacturers Association issued a technical bulletin in which it stated that installing their products over any unvented roof assembly is not recommended. At the same time, ARMA is conducting a 10-year study on shingle products over panels; their results won't be available until 2002.
On a personal note, I've had asphalt shingles over a mixture of vented and SIP roof on my present house for 12 years. After two years, a roofing inspector noticed that the shingles over panels were more brittle than the shingles over vented attic. After 10 years, a second inspector noticed no such difference, even when asked to directly examine for any differential in a "blind" test.
Your point about heat buildup does show up a bit. On a hot July day like today, with no air conditioning, the underside of the drywall beneath panels in my home is two degrees warmer (81 degrees F) than the underside of the vented attic drywall (79 degrees). (NOTE: this differential is not noticeable during the winter when the furnace has not been operating.)
Two possible measures for your consideration. First, to reduce any summertime concerns, select light-colored shingles for placement over SIPs. Second, at least one manufacturer (Winter Panel Corp.) recommends that any SIP roof be vented by adding vertical 1-bys plus a layer of OSB before felt and shingles, thereby creating a "cold roof."
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Jim Woodrow
Registered Users
New Member
Posts:2
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| 07/11/2000 10:52 AM |
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Steve:
Have you ever tested the temp. under the shingles on the two roof systems you have on your home? If so, what were the differences there?
Thanks,
Jim
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S. Andrews
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New Member
Posts:1
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| 07/11/2000 8:12 PM |
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Jim, I haven't tested right beneath the shingles, but will do so on Thursday or Friday and post it by week's end. I have tested at the OSB/foam interface, about 1/2" beneath the shingles, during a hot summer day; there is no comparable way to test a vented attic, but I'll do a proxy of that as well. Steve
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Steve Andrews
Registered Users
Basic Member
Posts:334
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| 07/14/2000 6:37 PM |
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Jim, the temps I recorded on a sunny July day at a near-peak time (1:30 pm., which is 12:30 solar time), at the location you requested--between the shingles and panel facing--were as follows:
--167 degrees F beneath the shingles above panels;
--163 degrees F beneath the shingles above a vented roof.
(Same color shingles, same building orientation, same building, with different roof assemblies.)
The temp either above or beneath shingles over panels is higher than above a vented roof. However, there's a larger difference between the temperature of light-colored shingles (174 deg. F) and dark-colored shingles (187 deg. F) than there is between the same shingles over vented and unvented attics. While the data here are extremely limited, it supports the notion that when it comes to shingle operating temperature, shingle color may matter more than roof assembly design beneath the shingle.
Note: a longer version of this explanation, along with descriptive tables, will soon be presented elsewhere on this website.
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Don Miller
Registered Users
New Member
Posts:1
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| 07/23/2000 7:12 PM |
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Thanks for this interesing thread.
We are researching newer construction techniques prior to building our retirement home.
While living aboard our boat for several years, I was astonished to discover the power of radiant energy from the sun.
Our boat deck was white gelcoat with fiberglass cored construction using a 3/4" end grain balsa wood core. Below this was an airspace with 1/4" plywood ceilings below.
We discovered it was much more comfortable in summer after a layer of aluminum foil was placed in the airspace.
Thin kitchen aluminum foil appeared to reflect back the sun's long wave radiant energy which penetrated this deck structure.
A second layer with shiny side down seemed to reduce heating requirements in winter by keeping more radiant energy inside.
It would seem adding a layer or so of aluminum foil might be a beneficial when we build.
I wonder if aluminum foil has been used immediatly under shingles on SIP roof panels.
Thanks,
Don
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Steve Andrews
Registered Users
Basic Member
Posts:334
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| 07/24/2000 10:44 AM |
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Don, you can't really place aluminum foil directly beneath the shingles because for any reflective surface to do its work it needs an airspace on one side or the other.
Research has shown that radiant barriers (that's the name for this concept) work best:
1) in very hot climates, from Florida to Yuma;
2) when placed BENEATH attic plywood (there's your air space).
Foils are low-emittance materials, much like low-e windows; they don't want to let the roof assembly radiate down to the attic insulation and pass on into the building through the drywall. The reason you put the foil BENEATH the attic plywood (even attached to it: KoolPly is an old product name) over time dust gathers on the top surface of the foil, which will slowly reduces its reflectivity (by eliminating its "air space." No air space and foil doesn't work.
For foil to work with SIP panels in a very hot climate, you would need to vent the panels by placing 1-by firring strips on top of the panels, then either Koolply decking or a combination of a foil product and then regular OSB, followed by your finished roofing. If in a very hot climate you are committed to dark-colored shingles (not a good idea over EPS SIPS; see July column in the News section), then venting your roof with a radiant barrier component would be a good idea.
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