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richntiff
Registered Users
Posts:28
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| 04/01/2008 2:03 PM |
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Hi all - been lurking some time, now I have a few questions. First of all let me say thank you all for the HUGE amount of info here, it's been very helpfull!
My planned project:
2100 SF home, total 4bd, 3bath including a mother-in-law style suite for my aging mother. I have considered ICF, but in my climate (northern Wisconsin) I debate the actual energy savings of ICF due to the fact that thermal mass does not seem to give a big advantage when exterior temps stay below indoor ambient for, oh, 7 months straight :-) So, now looking at SIPs and I have a few questions:
1) Roof assemblies - I LOVE the idea of a SIPs unvented roof, but cannot seem to find a SIPs roof panel that is over R-40 in rating. In my neck of the woods, R-38 is a min and it's becoming common to go above that. I want R-50 minimum. I've kicked around the idea of a SIPs roof with extra foamboard on the interior - then sheetrocked for fire rating. I can't see that I'm creating a moisture issue with this, but am I missing something? What are the options for placing standard architectural shingles on a SIPs roof - do I need to build a 'cold roof'? Due to heavy snow/ice conditions here, I dislike the idea of a cavity that is vulnerable to ice/snow buildup due to blowing/drifting snow. Second option is standard truss/sheathing roof - place ceiling drywall, then spray 2.5" of polyicynene foam in the truss bays, then blow 12-15" of cellulose on top of that. Anyone have experience with that type of assembley? It would be a vented roof, obviously.
Basically, I'm looking for ideas as to the best roof treatment, bearing in mind I attempting to owner/builder this house for a max of about $90/SF, on a full basement.
2) PU vs EPS panels. I want PU panels due to thinner walls eliminating need for extension jambs, etc. As a ROUGH guess, does anyone have an estimate of approx. how much more a PU panel runs per SF than an EPS panel? I know this is highly subjective, but it would help give me an idea if it's even feasible.
Thanks!! |
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PanelCrafters
Registered Users
Posts:1323
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| 04/02/2008 7:23 AM |
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Posted By richntiff on 04/01/2008 2:03 PM
I have considered ICF, but in my climate (northern Wisconsin) I debate the actual energy savings of ICF due to the fact that thermal mass does not seem to give a big advantage when exterior temps stay below indoor ambient for, oh, 7 months straight :-) So, now looking at SIPs and I have a few questions:
1) Roof assemblies - I LOVE the idea of a SIPs unvented roof, but cannot seem to find a SIPs roof panel that is over R-40 in rating
You are correct about ICF's(no advantage in the case that you described). Congrats on that! Many manufacturers(Enercept is one) make a 12.25" roughly R-50 EPS SIP panel. In addition to the increased R-Value, it will also span further.
Good Luck! |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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JBS
Registered Users
Posts:7
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| 04/02/2008 8:52 AM |
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I would not have a problem with the 2.5" of spray PUR and a good layer of cellulose, especially given the budget you've stated. But, it is you the homeowner that needs to weigh the savings of that system with other considerations. If you are possitive that flat 8' or 9' ceilings are just fine - there will be no attic areas or vaulted spaces - then sure, I think it is reasonable.
In your climate, I would definitely recommend a vented roof system.
PUR to EPS. My experience is that the polyurethane job of similar R-values is going to be $0.50/sf to $1/sf more than an eps job.
Jay
The Murus Company |
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trigem1
Registered Users
Posts:50
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| 04/04/2008 7:27 PM |
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You actually have quite a few questions here. OK, R-Control makes a 12-1/4” thick panel that has an R-Value of 44.7 at 75 F, and 48.3 at 40 F (see http://www.rcontrol.com/SIPs/energy.asp). If you’re planning on a vaulted ceiling, you wouldn’t need to do any extra ventilation. If you’re not planning on a vaulted ceiling, I might just build a conventional roof, ventilate it, and put down a layer of R-38 batt insulation, and then a layer of R-19 batt insulation over that, over the ceiling of your top floor. That should give you a combined R-value of R-57. Remember that when you build a tight SIP house, you will need a whole house ventilation system.
Many people swear by the cold roof, and others think it’s a waste of time. Personally, I think with a SIP roof, the expense of a cold roof can’t be justified. I usually recommend covering the whole SIP roof with ice and water shield to prevent moisture reaching the OSB. While both shingles and metal roofs are good options, I’ve noticed in some climates with wide temperature swings during the day, a metal roof will expand and contract, loosening the roof screws. If you don’t mind the snow sliding off the roof in a small avalanche, go with metal. If you don’t mind the snow on the roof, go with shingles. Also, I think the extra snow on the roof might add a little insulation value to the roof. I like the contractor grade 30 year, or more, shingles.
If you were to go with EPS 6-1/2” walls, just order the windows with a 7-1/16” jamb. Most window manufactures will do this. Although XPS has a higher R-value than EPS per inch, XPS is more expensive per R than EPS.
Steve
GrandCountySIPs.com
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Dick Mills
Registered Users
Posts:124
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| 04/04/2008 8:19 PM |
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Steve,
Is XPS heavier for the same R-value (uses more Polystyrene to achiece the same R-Value)? Is that why it is more expensive?
Dick Mills |
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PremierC
Registered Users
Posts:10
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| 04/05/2008 9:55 AM |
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richntiff,
I agree mostly with trigem1. If you don't want a vaulted ceiling go with trusses, vent it out. There are some options with a panel roof even if you don't want a vault all the way through your house. We have put ceilings on top of rooms like bath rooms or bedrooms and created a conditioned attic space above these rooms. We have installed steel roofs and shingles on panel roofs and to this point we have not had any steel screws loosen up, we are in MN. There are several companies that make 12" roof panels out of eps, and they all should be in that 45 - 49 R- value. EPS panel perform better as it gets colder. 12" @ 75 degrees R-46 , 12" @ 40 degrees R-47 this is according to Dept. of Energy scientist at the Oak Ridge Labratory. This study was done 1996. If you have a chance sometime grab a hold of a eps panel and lift. Then grab PU panel and lift. The PU panels are much heavier to handle.
Chris
Premeir Construction |
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richntiff
Registered Users
Posts:28
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| 04/05/2008 11:05 AM |
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Thanks for the responses guys - we are not too crazy about vaulted ceilings - I'm planning a 2' tray in the greatroom and a 1' tray in the master bedroom. Other than that, either 8' or 9' ceilings (yet to be decided). My gut feeling is we will go with a conventional roof structure. I won't install a steel roof in this climate - they do have some nice advantages, but as noted above - they are prone to producing avalanches on your porch,etc - I've seen some substantial iceing issues with them on friend's houses.
I guess my thought on EPS vs PUR panels is which one comes out more economical once I figure in extra cost for PUR vs. extra cost for extension jambs. We won't have a ridiculous amount of windows like is so common nowadays, so in all likelihood EPS will be the choice.
Thanks again!
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trigem1
Registered Users
Posts:50
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| 04/05/2008 3:14 PM |
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Dick,
EPS and XPS are made from the same plastic (polystyrene), but the process is different. EPS begins as small plastic “beads” that are expanded and fused together. It is the same as the white foam in many disposable coffee cups.
XPS begins as a continuous mass of molten material. It is familiar as the yellow foam used in trays for fresh cuts of meat at the supermarket.
So, R for R, they weigh about the same. The proccess to manufacture XPS is more expensive. XPS is extruded, while EPS is expanded.
Steve
GrandCountySIPs.com |
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