I have been trying to decide on construction of our new home and have looked at everything from the odd(monolithic dome) to conventional construction.Although i have not made up my mind yet i keep coming back to my original idea of an icf wall with steel truss's with metal roof. I have a friend who builds homes and a lot of them have steel roofs.He sprays 1 inch of closed cell foam directly against the underside of the metal roof and then insulates the attic with batts or blow in insulation.I don't know how efficient this is but he hasn't had any problems doing it this way. My idea is to spray 6 inches of open cell foam directly against the underside of the metal roof and totally seal the attic.Would also spray some on the trusses themselves.Is there a problem with doing it this way ? I was trying to get away from having any osb decking or wood in the roof.If this is not acceptable what would be a good alternative. The metal roof would be 26 gauge metal sheets like you get from Mueller or like company's.What some would call barn metal.Not much standing seam metal roofs in my area and it is out of my budget anyway.I am located in southern oklahoma. Appreciate any idea's. thanks

klavoy; your idea will work use steel purlins over steel trusses to get away from wood.

Since you are in a storm area you might want to consider using closed cell foam. It will add strength to the roof. Hold off on spray foaming the roof until after a few rains so you can check for leaks.

If budget is a concern, I'd look at either cellulose in a vented attic or mostly rigid foam (vs so much spray).

I appreciate you folks taking the time to answer my questions and giving me some ideas. Take care.

If your open to the dome approach I would recommend you go to econodome.com.  This is a dome kit without hubs, but the braces intercept at the hub point. 

I've seen some of these go up for as little as $30/sf on crawl space + land.  They do not use shingles.  I would build one in a heart beat if I had the money.

I have to ask why barn roofing is cheap and standing seam is expensive. If the steel has the same thickness and coating, shouldn't the price be very similar?

jonr; it sounds logical, the only thing that might make a price difference is the roll forming may be more complicated and takes longer as each piece is much narrower

jonr, chris partially correct. The major concern in pricing difference is the thickness of the metal.
Most barn metal is 29 gauge (some is 26). However, most standing seam is 24 ga. with some being 26.
The thicker metal makes a big price difference. Add in the complications of forming and the accessories costs,
and the price adds up quickly.

Wes; jonr's question was "if the metal was same thickness and coating the same" an apples to apples comparison so to speak , then the only conclusion would be the roll forming process for standing seam takes more time in that the panels are usually only 12" - 16" wide and would run up the cost per sq. ft. as compared to a single wider panel, 2-3 times more handling, stanting seam also needs crated as opposed to just dunage & strapping

Sorry Chris,
I read jonr's question to be: IF they are the same gauge and finish.
My point is that barn metal is almost always thinner and, many times, the finish coatings are of lesser quality.

Thanks. Looks like standing seam is double the price (materials + shipping, $215 vs $425) for the same thickness and coating. The main difference is just hidden, less likely to leak fasteners, right? And then there are the sometimes outrageous installation prices. I know nothing about it, but it seems like metal panels would be easier than shingles.

Forming isn't that expensive. The formers can even be portable. They come to the job site and turn out metal off a roll all day long. Sheet metal is still a commodity.

Metal gauge - 24g, 26g or 29g
Galvalume or not
Siliconized polyester coating or Kynar.

That's basically it, as far as product goes; the rest is marketing, insurance and profit.

it seems like metal panels would be easier than shingles.

It does seem like it, doesn't it? When you slide a sheet metal panel up, you might cover 50 sf at a time as opposed to a shingle which is a few sf. Best as I can figure, metal takes two guys who have some skills. Shingles takes one guy who sorta knows what he is doing and a bunch of cheap labor. I've watched some roofers. Metal takes a long time for each job- usually more than a week, but there is a small crew. A shingle crew can do a shingle job in a day or less. More jobs, more profit. With metal, more profit has to go on each job.

I've gotten reasonable quotes from small two-man metal roofing outfits. The big companies don't seem to want to do the residential metal unless they get A LOT.

So maybe $10,000 is reasonable for installation for some roofs - 100 man hours times $100/hr. And there are stone covered metal shingles which give long life with the shingle look (and I assume installation prices similar to asphalt shingles).

The steel SIP manufactures bond metal to foam - perhaps glue on metal roofing is feasible (no fasteners and no premium for standing seam).

Posted By jonr on 01 Aug 2011 09:06 AM
So maybe $10,000 is reasonable for installation for some roofs - 100 man hours times $100/hr. And there are stone covered metal shingles which give long life with the shingle look (and I assume installation prices similar to asphalt shingles).

The steel SIP manufactures bond metal to foam - perhaps glue on metal roofing is feasible (no fasteners and no premium for standing seam).

jonr;

Installation of stone coated roofs are different than asphalt, we have installed several stone coated shingle roofs and they are much more complicated than any standing seam metal roof.

I don't know of any manufacturers that approve using foam as an attachment.

There are some concrete tiles approved that way

The 1" closed cell + fiber approach your friend is using is the better value-proposition than an all open-cell solution, and more reliable. Open cell is too moisture-permeable, and wintertime condensation events at the steel/foam boundary will be common and could cause separation of the foam from the steel over time (especially during freeze/thaw situations, which will be common even in OK, sometimes even when air temps are a few degrees above freezing outdoors.). But with an inch of closed cell the condensation events will be less often since the condensation surface is exclusively at the foam/fiber boundary, where it can't damage anything. The extra rigidity & vibe dampening of closed cell on steel makes it considerably quieter during rain & hail events too.

The thermal bridging of steel trusses is several times that of wooden trusses, which may warrant shooting them with 1" of closed cell too.

Well, I thought every thing was looking pretty good until Dana presented his information that the foam might not stand up to condensation with open cell foam sprayed directly to the metal. Anybody else have any information or thoughts on this succeeding or failing ? Appreciate hearing your ideas.

Best to contact a manufacturer and ask about that application.

A foam supplier that I use recommends putting tyvek (or eq.) over the frame before applying the steel roofing (or wall) panels. Then the foam is sprayed onto the tyvek. He likes it because if the steel panels have to be removed or replaced, it can be done without distroying the insulation. Would this not put the condensation between the steel roofing and the tyvek, and keep it away from the insulation?

Wes, That is an interesting concept of using the tyvek as a spray barrier.If you don't mind my asking does your foam supplier use open cell or closed cell ? Also i wonder how much tyvek could handle if a person used a thicker amount of foam.Im assuming if the tyvek was used against the metal roofing the heat generated during summer would not hurt the tyvek. thanks