I am in the planning stages for a home to be built on family farm in southeast Minnesota. It will be a rambler with walkout basement and approximately 3500 square feet total. I am thinking of building all exterior walls with ICF. I am unsure of what to do for a roof and insulation. I am looking for advice on the most economical design. I am assuming this would be rectangular shape with a simple gable roof. I had also considered doing a single slope ICF roof but was concerned about the cost. Any input would be appreciated.

A Insuldeck type roof is definitely going to cost more then trusses even with spray foam. Most projects with ICF walls have trusses and it is recommended to use spray foam.

A box is the cheapest thing to build, but from an ascetics point of view...add some flair

Back when we were in the design stages of our house I had read how expensive it is to do a concrete roof and almost ruled it out. We went with a single slope quad deck roof cost us $13.60/sq ft for everything--12.5" forms, rebar, concrete, pump, extra insulation to r52, waterproofing,thermal break, bracing. Only thing this does not include is labor as we did it all ourselves. Roof was a fairly simple design, mostly rectangular (minus a corner), 2ft. overhang all the way around, extra 5 ft. rounded overhang over front door. Hope this helps

Posted By ksandjs on 05 Jul 2014 06:48 AM
Back when we were in the design stages of our house I had read how expensive it is to do a concrete roof and almost ruled it out. We went with a single slope quad deck roof cost us $13.60/sq ft for everything--12.5" forms, rebar, concrete, pump, extra insulation to r52, waterproofing,thermal break, bracing. Only thing this does not include is labor as we did it all ourselves. Roof was a fairly simple design, mostly rectangular (minus a corner), 2ft. overhang all the way around, extra 5 ft. rounded overhang over front door. Hope this helps

For just parts, no labor, that sounds about right. An InsulDeck roof usually runs $22-$27 per square foot (depending on sqft area and complexity/slope) but that is including labor. Labor is usually double the costs of parts. So $13.60 without labor would be $27.20 with labor.

In most cases an ICF/Insuldeck roof is overkill but if you live in a hurricane region or just want that castle like design, it can be done. It's not cheap and it's definitely not a DIY if you don't have any experience in such concrete work.

Posted By sparky on 02 Jul 2014 10:32 AM
I am in the planning stages for a home to be built on family farm in southeast Minnesota. It will be a rambler with walkout basement and approximately 3500 square feet total. I am thinking of building all exterior walls with ICF. I am unsure of what to do for a roof and insulation. I am looking for advice on the most economical design. I am assuming this would be rectangular shape with a simple gable roof. I had also considered doing a single slope ICF roof but was concerned about the cost. Any input would be appreciated.

As mentioned, ICF/Insuldeck concrete roofs are not cheap and require engineering. If you are looking for hurricane or tornado resistance, that is the way to go for a roof.

I believe the next best thing to a concrete roof is a SIP roof. Structurally, they are stronger than a stick frame truss roof and are quicker to put up and give you a conditioned space. You can go wood/OSB SIPs or Steel SIPs. If you do the OSB SIPs I would go the route of using polyurethane and if you go steel SIPs you will usually have EPS for the core. You get your overhang and soffit with a SIP by simply overhanging the SIP on the ICF wall. One can go 24" cantilevered without any issues. If you do SIPs you will need to incorporate interior beams, usually glulam if exposed.

SIP roofs (depending on square footage and R-Value) will run an average of $9 - $14 per square foot. Some areas can run a little less or a little more depending on plant location in relation to the project location.

Posted By Lbear on 05 Jul 2014 11:59 AM

Posted By ksandjs on 05 Jul 2014 06:48 AM
Back when we were in the design stages of our house I had read how expensive it is to do a concrete roof and almost ruled it out. We went with a single slope quad deck roof cost us $13.60/sq ft for everything--12.5" forms, rebar, concrete, pump, extra insulation to r52, waterproofing,thermal break, bracing. Only thing this does not include is labor as we did it all ourselves. Roof was a fairly simple design, mostly rectangular (minus a corner), 2ft. overhang all the way around, extra 5 ft. rounded overhang over front door. Hope this helps

For just parts, no labor, that sounds about right. An InsulDeck roof usually runs $22-$27 per square foot (depending on sqft area and complexity/slope) but that is including labor. Labor is usually double the costs of parts. So $13.60 without labor would be $27.20 with labor.

In most cases an ICF/Insuldeck roof is overkill but if you live in a hurricane region or just want that castle like design, it can be done. It's not cheap and it's definitely not a DIY if you don't have any experience in such concrete work.

take with a grain of salt any type of cost that lbear reports.  he has built zero homes.  he lives in a strange reality when it comes to pricing.  for example, if you give your actual numbers, he will say that either you were ripped off, or they didn't do something because it doesn't agree with his "numbers".

How much of the 13.60/ft is the forms?

msteffen, I'm no help but I'm thinking that a minimally pitched roof can be useful and likely worth the additional expense if it can be made accessible and waterproof while holding up to foot traffic.

Posted By mojoe on 16 Jul 2014 12:24 PM
How much of the 13.60/ft is the forms?

I got a quote from the southern california distributor for Amdeck, and he was charging me $5.25 per sq ft and $3.25 per linear ft of c-joist.

There are 2 joists per block with each joist 2' long per block.

The block is 32"x24" = 5.33 sq ft

4 * $3.25 = $13/5.33 = $2.44/sq ft for the c-joists
                                      $5.25/sq ft for the block
total  =                          $7.69/sq ft not including tax or shipping. 

I think shipping is not a small amount, but in the end, I used a builder, so I never found out about the shipping cost.

Hopefully, my math is correct.

of the $13.60 for 12.5" thick forms cost us $5.60 sq ft.

Thanks for the info.