Hi, All, First timer, first message, first question. :) Really like ICF, plan to use it above grade to the roof line. Send my structure engineer the plan, he told me no, I can not use truss roof because of ICF. His opinion is like since the ICF wall itself is too heavy, the truss is not strong enough to hold them together in earthquake, thus need to have a flat roof. I am skeptically about this as my understanding is ICF is mainly rely on its internal steel for strength, and this guy is kind of young too, only worked with ICF for basement in the past. And I saw so many ICF applications without special consideration on the roof truss so want to hear 2nd opinion. Have you heard this before? Also, if know any experienced ICF structure engineer, especially above grade, in Vancouver, BC area, please recommend. Thanks! Bill

Call the guys from Quad-Lock. They manufacture and sell the product up there, so they can tell this guy is full of poop. Also call the guys at Fab-Form, besides all their great products I believe they are Nudura distributors and they will also tell you this guy is full of poop and can set you on the right path. I told my mother I wouldn't say that other word. Also as I posted today for another person, you can put the trusses down between the two walls instead of on top and they become diaphragms.

Thanks, Smartwall. I have attended fab-form ICF training and they have giving me a firm in Ontario for reference which I left message but not heard back yet. But still, in BC I bet I will need local registered engineer to review and stamp the design so not so sure how much Ontario firm can do. Anyway, I will give Quad-Lock a call tomorrow when everyone is back to work.

I have never designed in an earthquake area but have a question. Does the house have long straight walls? Each corner that is add will add strength to the wall much like a piece of paper can hold itself up but if you put a fold in it then it will hold itself up fine.

Can you add some internal ICF walls to bridge across? How about adding more rebar or wall thickness. How thick are you going? how about some steel beams that can tie the walls together at the top? You could cover them with wood later and make them look nice.

My building department wanted shear walls installed at first on our ICF house and then I sent him a report on ICF walls with a garage door opening cut in it and it was still rated at 10 times the shear strength of wood. He let it go right away.

Good luck with this. I think there are many options.

no long straight walls, it is two story with basement. lower story is like a square box while upper story have to corners cutout as plan extends out, where I would be using wood structure instead. See attachment I have a 3d render of the walls, thx for VancouverICF.

As always, Smartwall will set you straight with all things ICF. I learned a lot from Smartwall over the last decade on this forum...intelligence plus experience leads to wisdom… We designed our single level ICF home for a 9.2 earthquake and we used 40’ full span 6/12 roof trusses. Just a rectangular 40’ x 60’ ICF building envelope and lots of big windows on the south side for passive solar cooling/heating and the view... It is the footing size and wall rebar schedule that largely determines the structural strength and earthquake resiliency. You also need to use the appropriate hardware to allow the walls to move independently from the trusses. Rigid structural connections tend to be bad in earthquakes. This is true even in locations not subject to earthquakes as roof trusses have seasonal truss uplift that will crack your ceiling/wall drywall if not properly addressed.

I agree, your design has plenty of corners, it should be incredibly stiff.

How much more does your engineer want to do a poured concrete roof? Maybe he just wants to have one under his belt?

Posted By smartwall on 12 Oct 2020 06:06 PM
Also as I posted today for another person, you can put the trusses down between the two walls instead of on top and they become diaphragms.

I want to research that, what would you call a roof that is bolted on top? I need a search term for diaphragm vs. X. It seems weird, bolting a roof truss on top of a wall seems like the connection could be a lot stronger since it is bearing directly on the concrete instead of the insulation and can have a J hook. A truss between walls could probably handle compressive loading better but not by all that much, it just has a little bit of foam to back up the shear strength of the nails/screws in the joist hanger. I want to understand this. There could be something staring me in the face but I'm missing it.