Concrete is fine for your roof system as long as it is Flashed and Waterproofed correctly. Concrete itself is very absorbent and will wick water farther then you want to know. Most people opt out of a ICF roof because of cost vs stick frame. Hard to compare concrete to wood frame in my opinion. Nd96 has a good point. Designers now a days make the roofs so cut up for aesthetic purposes that it makes it more difficult to do out of concrete. Nothing is impossible as long as your budget will allow it. I like the walls and floor idea, that gives you both advantages as is prob cheaper then doing an extremely cut up roof with 45's etc.

The question that you really have to answer for yourself is "what is most important to you about your roof?" are you looking for the best natural disaster resistance? or The highest possible insulation value? If you want your whole house to be a proverbial safe room, then keep going towards the concrete roof option, and design the home and roof to accommodate the concrete design and try to keep the room a little less complex. If you are looking to have the highest roof R-Value on the block, stick or SIP may be a better option for you. Option 3 which is done primarily in Tornado alley is a concrete ceiling, with a sacrificial gable roof atop it.

Make sure to research to benefits and differences between insulating the roof vs. the ceiling.

look at the GigaHouses and the GigaRoof, they can be used on ICF homes and they are disaster resistant

I did this mistake. I built a stick roof on top of my ICF house. I am afraid of walking on top of my roof now.

Posted By R9tobon on 16 Jul 2012 03:02 PM
We thinking of doing a flat roof since my understating you can get not get a high pitch roof with ICF.  What you’re thought on a flat ICF roof? I would not think there be any leakage problem since it Concrete and has no wood for it to rot out.

The only reason wood will rot is if it gets wet, which of course is the antithesis of what a roof is for! Wood rot is not something to be concerned with.

Obviously, concrete is heavy. A concrete roof will add significantly to the load on the wall footings so you have to take that into consideration. You may have to have footings 50% to 100% wider than with a wood roof. With the size you're mentioning you may have to have intermediate support walls just for the roof. That may interfere with any open spaces you're designing in.

Posted By samix on 17 Dec 2012 12:48 PM
I did this mistake. I built a stick roof on top of my ICF house. I am afraid of walking on top of my roof now.

Why? I wouldn't be surprised if a built up flat roof is more vulnerable to foot damage than is a sloped asphalt shingle roof.