well, we have a meeting tomorrow night to start drawing our plans.  We are starting to iron out 'details' now.  Of course, every "solution" raises more questions.

here is our basic plan as it stands now.

basement - traditional poured foundation with foam board insulation under slab & on outside walls

walls - 6" sips

roof - raised heel trusses

I'll know more when I have the plans finalized & can get real bids, but the ballpark number I got was that for materials only, doing a sip roof would be about $15,000 more than the trusses.  Doing a sip roof, obviously insulation is included - with trussed roof I would need to insulate.  it got me thinking.  A sip roof should go together much quicker, so theoretically, labor costs will be less.  Insulation is factored in already, where I would have to pay for that separately with a trussed roof.  How much of that will "even out"?  My gut feeling is telling me that I'll get some back if I go with a sip roof, but it will probably still be $10,000 more.    Is it worth it? 

Another "issue".  the latest bid is from a panel manufacturer, but they don't install.  He said he'd work with my builder to make sure he's comfortable with installing them, but the builder has never done it before.   I talked to the builder today & sent him some documentation.  He's going to read up & said that as long as he feels that he's getting all the info he needs, he's ok with installing them. 

IF we would go with the sip roof, is there any reason for concern that he's never done a sip installation before?  The wall structure seems pretty simple to go up, but I'm not sure about the roof..

i would not plan on any labor cost saving with sips. while sips are somewhat quicker for experienced installers i find that
contractors who have not done it before will not bid any less than stick built.

that's kind of what I was expecting to hear. So as far as I can tell, the only reason to look at doing a sip roof vs trusses would be if sips would allow us to utilize a smaller hvac system. If we spray foam the trusses, I can't imagine there would be that much difference in heat loss, would there?

jerkylips
With the preliminary design you posted standard trusses sprayed with foam will work fine and will be very easy to install. As for the difference between sips and sprayed foam performance: You are heating the same space so the only thing that is different would be the conduction through the trusses themselves @24" oc. Keep in mind you would only need raised heel trusses if you were going to blanket or blow in lose insulation. Don't do raised heel trusses with sprayed foam for you would be wasting your money. As I said in a previous post you would be wasting monies with sips with this roof design.

thanks, good to know.  I must not understand the concept of raised heel trusses, though - I don't understand why they'd be good for blown in insulation but not needed for sprayed in?

About conduction through the trusses.  there are several points where the lumber will be hitting the drywall & also the outer skin of the roof, but it's not like a wall, where they're in contact across the entire length - so that should minimize the thermal bridging, right?

With raised heel trusses your insulation is on the ceiling and to get enough thickness (height) you have to raise the heel of the truss so the increased insulation will fit. With sprayed insulation you do not need the height due to the fact the insulation is on the bottom of the roof deck between the trusses. As for conduction points the drywall has no bearing on the "energy short circuits" if you are spraying the bottom of the roof deck. If you are insulating the ceiling (where the drywall is) than there is a decrease in r value at the truss or rafter.

I was told by my Walltite provider that anything over R40 is not necessary and you start to run the risk of the outer foam freezing. As long as you have 7-8" at the edges of your trusses you should be okay, my raised heel are 20" so it's just a little extra required around the perimeter. If you get the raised heel you can add some blown on top. I would agree, I bet he could put up the trusses a little faster an easier just because thats what he's used to. I think a properly installed SIP roof would be great, but I wouldn't want to be his first. Sean

Thanks for all the replies!!

I'm still trying to learn as much as I can about this so maybe I'm being "dense".  It seems every answer is making me think more and ask more questions. 

The house will have a combination of vaulted ceilings and flat ceilings.  When I asked the original question, I was thinking specifically about the vaulted space.  It seems like the space between the bottom of the truss & the roof deck is going to be probably 12-18", max.  I was assuming that whole cavity would be spray-foamed.  Would that be overkill?

Also, how exactly do you insulate the spaces above the flat ceilings?  On the underside of the roof deck or directly on top of the ceiling?