I am currently designing my house, which I plan to build with ICFs. However, I'm concerned that the roof area becomes the weak link in the chain. After looking at Spider Ties roof solution, I came up with the idea to use ICF's for the roof. Like Spider Tie, Stick frame the roof, sufficient to handle the concrete weight. Than fasten ICFs to the roof deck. It would seem that this would be a better option than using one of the concrete decking solutions. Has anyone ever tried this? only seems logical, as it provides all the same benefits: air tight, rigid insulation, thermal mass and serious protection against a Hurricane. Spider Ties solution requires plywood decking on the top that than gets removed. With the ICF, i would just fasten 1x6 decking to the ties to provide nailing for the slate roof. Roof pitch is 14/12 and 16/12 and I plan to use real slate for the roof.

When you say weak link are you referring to thermal performance, hurricane resistance, or what?

Framing under concrete doesn't make sense to me. Sorry. And 14/12 and 16/12 pitch? That's like an A-frame. You will either have short walls or a very high ridge. In my mind something just isn't adding up.  Maybe I'm just dense or naive.

See attached sketch. Ignore the gaps in the ICF at the wall, roof transition, ICF's are blocks in Autocad. Energy performance is #1, than storm protection. My original plan was to use closed cell spray foam, directly under the roof deck.

I am in planning stages to build a small vacation home in Florida. There are several ICF vendors (e.g., AMVIC AMDECK, BuildBlock BuildDeck, Quad-Lock Quad-Deck, Liteform LiteDeck, etc.) making ICFs for roof/floor. I am looking to build a house with a shed roof (so the top of the roof is not visible from street), and not use any roof shingles at all (just the exposed concrete). I may add stuff to the concrete mixture for water proofing or cover the roof with white color EPDM. I feel adding shingles defeats the idea of building an ICF home that can survive hurricanes without any damage.

z_zk_z,
Good point. Be careful with cracking - meaning water leaks. Maybe add steel fiber to mitigate this. A good waterproofing additive also. And I would probably use a sealant on the surface...

mbtracy,
Neat idea. I think you shy away from ICF decks as the slab provides no attachment surface for roofing.
However, the strenght of the roof would come from the depth of the concrete beams - or in your case it would be a flat slab from steel joist to steel joist... 4" slab (4" ICF form) may be OK with joists spaced at 3 feet max - better make it 2. Going to a 6" form would bump up the weight of your roof tremendously. Not sure if that is a good idea... Steel joist spacing may go up to 10 feet - check me on that.

This is the structural advantage of an ICF deck. Deep concrete joists - no need for steel joists. Much less concrete needed.
So what do you do...? Here's a rough idea...

Concrete shrinks as it cures and results in small gaps around all the plastic ties that hold the two sections of foam together. You have to have another form of water proofing to stop the water. Also foam isn't UV stable so you will have to cover it. Maybe you could water proof from the underside/inside?

Baldwin2014
very interesting idea, awesome in fact. correct, ICF decks like Amdeck or Insuldeck don't provide an easy way to "form" the concrete during the pour, hence the idea of using the ICF block. To be honest i stole the idea from Spider Tie. They have a great design for roofs, but it requires removing the plywood decking, which doesn't sound fun on a 14/12 or 16/12 roof. The ICF unlike spider tie, allows an easy method for screwing plywood decking or in my case, 1x6 decking for the slate roof.
Logix just posted a study on the performance of ICF vs wood framed wall and the thermal mass of the wall plays a big part of the overall performance. So seems logical to use ICF on the roof. Just not sure if the "labor" is worth the investment.

Actually, the Spider-Tie system allows you to keep the exterior OSB/Plywood sheating as a nailing surface.

The only problem becomes thermal bridging from the roof surface into the wall cores.

Quad-Lock and Spider-Tie generally recommend an exterior layer of insulation if you're worried about this.

Or maybe a something like (assuming a simplified roof layout):

* Concrete form roof slab with the OSB/Plywood sheath left on. In the case of the Spider-Ties, screwed into the webs. The peak would be "benched" flat and fasteners for a wood/steel beam attached.

* If you want to be paranoid, apply some roll-on waterproofing or use asphalt impregnated sheathing.

* On the bench at the top, drop a wood/steel beam and fasten it to the concrete roof structure.

* SIP panel exterior sheath secured to the concrete sheath layer with construction adhesive and nails at the joints.

* As you've already likely got insulation both in AND/OR underneath the concrete, you don't need some ridiculously thick SIP panel. You may also be able to get away with larger panels and less faux "rafters" between the panels.

* Frame out, water/ice-proof, roof and gutter as normal.

Probably ridiculously expensive and over-engineered.

But a setup like this would deliver a very strong roof system that could survive major weather incidents (as the concrete's going noplace), and at worst, needs replacement of the SIP shell. It would also mitigate the thermal bridging issue.

But, aside from the massive overthink and probably expansive cost, can anyone think of a reason why something like this wouldn't work?

What is your plan for out of plane restraint of the walls? That is a lot of weight in CC pressing down and out on the walls...

Posted By ronmar on 08 Apr 2017 10:37 PM
What is your plan for out of plane restraint of the walls? That is a lot of weight in CC pressing down and out on the walls...

You still need a truss/rafter system underneath the roof.

mbtracy

Can you explain what are the reasons for not using a deck ICF solution for the roof - such as Amdeck, Insuldeck, etc?
Thermal bridging can be dealt with by installing EPS foam panels on top of the concrete roof after the concrete has cured.

If you really need a bunker why not have a flat concrete roof deck?

Energy efficiency is important to me, hence the choice to go with ICF. However, I am an architectural snob! Design is very important to me, in fact i am aiming for a "Period style" house. European Chateau. So of course flat roof is out. Amdeck, Insuldeck, etc. seem better for flat roofs/floors. Utilizing them on a steep slope seems impractical, between holding the concrete to the formwork and the bracing. It just seemed logical to me that if an ICF wall works on the vertical, why not use it on a 16/12 roof pitch. By framing the roof first, the rafters provide a cavity for wiring, ductwork, etc. Like i said, I developed the idea after looking at SpiderTie's solution. Their solution works great with Light Weight Concrete, just nail shingles directly to the concrete. However, considering the challenges with sourcing Light Weight Concrete, which means i can't nail into it, i figured why not ICF. The webs provide a nailer for the roof deck, which will be 1x as recommended for slate.
Just thinking outside the box, its what I do both in my Professional life and Personal. I spent over a year building a 75' Bridge, DOT spec, to enter the property.... pretty all with my own 2 hands.

Everyone agrees ICF's are superior, however if the Roof envelope is the #1 culprit for energy loss, why not leverage the ICF for the roof as well. I realize concrete is heavy, however the guys at SpiderTie do use their system with regular concrete with success...

Concrete at that pitch is certainly lots of weight. Buttresses would be important consideration. You say flat roof is out. Is that just exterior or interior. If you can accept flat interior, just put a flat concrete deck roof and than set a standard wood frame truss atop that.
Alternate considerations might be steel skin SIPs or a structural steel roof.

Hello,
there are a couple of ICF contractors i know who have worked out an ICF roof system and slope is irrelevant, one is Nick Nickoforuk with IntegraSpec and the other is Eldon Howe with TotalICF, they both have pioneered the ICF roof technology
https://www.google.com/maps/uv?hl=en&pb=!1s0x8818df6f6ea6b5ab:0xeffeaed4b7d51eb0!2m19!2m2!1i80!2i80!3m1!2i20!16m13!1b1!2m2!1m1!1e1!2m2!1m1!1e3!2m2!1m1!1e5!2m2!1m1!1e4!3m1!7e115!4shttp://www.totalicfs.com/videos/!5stotalicf+-+Google+Search&imagekey=!1e1!2shttp://www.totalicfs.com/s/cc_images/teaserbox_4209347193.jpg?t%3D1416419860&sa=X&ved=0ahUKEwj65OLloqHTAhXGKiYKHcebB6AQoioIajAQ

For high pitch roofs, some contractors have used Quad-Deck with shot-crete instead of a stiff mix.

Why not build up the gable walls with ICF then frame up the roof with rafters supported by beams between the gables?
Then place 6" or 8" SIP panels on top which give you both insulation and support for attaching tiles.

In any case - in this day and age I don't believe there is justification for a mass concrete roof with a 16:12 pitch - its added weight and difficulty in execution cannot be justified by the architectural requirements alone as there are so many ways to achieve what you want.

I must be missing something. I just Googled European Chateau. The images I see all show multiple roofs with no gables, with lots of dormers, etc. To me it looks like it would nothing short of a nightmare to try build one of those with ICF.

Posted By dmaceld on 13 Apr 2017 11:31 PM
I must be missing something. I just Googled European Chateau. The images I see all show multiple roofs with no gables, with lots of dormers, etc. To me it looks like it would nothing short of a nightmare to try build one of those with ICF.

It'd take some planning.  But likely, the sticking point is going to be price.

And the roof is DEFINITELY going to need to be heavily engineered.  That will, also, likely, involve architectural compromises that the OP may or may not wish to make.

Curious...did you ever complete this project? What was the outcome? I am researching an ICF build next year and want to do total concrete envelope but like high pitch roof designs also.

ccmccoy, I think building a total concrete envelope with Structural Concrete Insulated Panels (SCIPs) would be easier and might cost less. Do you plan to build in the South or Southeast USA?