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FrankT
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Posts:1
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| 08/20/2000 2:41 PM |
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I have been looking into building with SIPS. Two companies have told me that due to roof design it would be very difficult and very expensive to use SIP roof panels.
I need to find out if it would be worth the investment to build the walls with SIPs, but not the roof. (would the cost of materials, ever be off set in energy savings). If I do go in this direction, what isulation considerations should I take. Also, would I have to take the same ventalation considerations i.e. air exchanger.
Thanks in advance for any input you can provide.
Frank T. Manteca,CA
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Steve Andrews
Registered Users
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Posts:334
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| 08/21/2000 1:42 PM |
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Frank, yes SIPs in roof systems cost more than truss roofs. The trick to narrowing that cost disadvantage is to either use a steeper roof pitch or combine short knee walls with a modest roof pitch such that you enclose usable space at a modest cost difference.
I've field-tested a fairly large variety of different wall systems. (By "field-tested," I mean I've used a blower-door in combination with an infrared camera and surface temperature monitoring devices to examine how a building is performing, with the objective of telling the particular builder how they could cost-effectively upgrade their current building system.) I know that a large number of those building systems can work well, when properly installed. But the devil is in those installation details.
You can build a home with R-7 foam sheathing and R-13 batts and have it perform very well, if the installers know the key details; however, the chances are the building will not live up to the energy potential of the installed products. You can upgrade to R-7 sheathing with R-13 sprayed cellulose and substantially increase the odds of obtaining good energy performance. You can upgrade to SIPs and further still improve those odds. Finally, you can install insulated concrete form systems (note: use ICFs with plastic spacers) which (in my experience) provide the greatest likelihood that you will obtain the energy benefits of the products installed.
As luck would have it, each of the measures listed above costs more money than the previous one. And each is also more "idiot-proof" than the previous one.
[Footnote: if you are concerned with energy efficiency, don't use steel framing, and especially don't use steel roof trusses, whatever the wall framing system you choose. Steel systems, popular in your state, are difficult to thermally isolate from the outdoor environment; that is just as important in Palm Springs as it is up near Mt. Shasta...]
One thing to keep in mind is that in the case of SIP and ICF wall systems, you have other benefits besides energy savings and improved comfort. The most notable of these is significantly enhanced strength in the face of natural disasters--winds, earthquake, fire, falling trees, crazy SUV drivers, etc. What's the value of that extra protection? Your call. Note, however, that a few insurance companies are apparently waking up to those strength advantages in the price of their policies to owners of ICF and SIP homes.
Back to your roof: remember that panels add an air-tightness advantage at the leakiest part of your building-- the roof. If you don't use panels in your roof, and you want more energy performance for your installed R-value than you get with the average builder-installed approach, try have cellulose blown into your attic instead of fiberglass; it adds a modest tightening advantage, though it isn't an air-barrer.
As for ventilation and R-values: where are you building in California? What is your heating fuel? Will you need AC? And which utility supplies your electricity. In many locations, you can't justify the cost of a heat-recovery ventilation system. In some situations, an upgraded exhaust-only system would be a good fit (e.g, American Aldes, use of the AirCycler, etc.).
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