I had a customer come to me with a contemporary design and a flat roof with a Lake Minnetonka view. He wanted a concrete roof (as well as the floor systems) on the ICF walls; either hollow-core precast plank or a cast-in-place on Lite-Deck or similar.

Would it work to install the concrete roof structure; the roof membrane over that, like EPDM; and pour 2-3" of concrete over the membrane. The topping could be stamped or stained.

Since the major cause of roof deterioration is sunlight, wouldn't the roof last a long long time? Would the small amounts of expansion and contraction cause a problem? Is this feasible? After all the is the preferred method of damp-proofing a garage floor or stoop when there living space below.

I would say yes its just like a precast garage with living space underneath. A friend of mine is actually the rep for the midwest for a firestone brand of rubber and we have been using it for years as our membrane in situations like this and has worked great. As far as the contraction and expansion I know when he teaches contractors how to install and there is an install technique that can make it a non issue I just dont remember what it was. So I think you are right.

icf4life,
have you done this in a place with full exposure to weather? I only have with stoops, most of which are covered, but it seams more extreme for a roof with much more sf.

This is done all the time.  You just need to design the structure to handle the appropriate loads.

Where will the roof insulation be?  I situations like this, I favor an "inverted" roof where the roofing membrane is installed on the top of the slab with protection board, insulation and then the concrete screed or other finish material like pavers.

It is best if you can get the slope (1-2% MIN) in the structural slab, although I have seen the slope made with a lightweight fill screed on top of the structure, which is probably what you would do if the roof structure is precast plank.

This way, your structure is warm and thermal movement is not a problem.  The insulation provides protection and separates the thermal movement of the deck from the membrane.

You will likely want to use a 2 level drain, especially with the stained concrete scenario.  While the roof surface catches most of the runoff, the roof membrane obviously need to be tied into the drain, too.

I miss Lake Minnetonka (not the winters. though)  We lived in Wayzata for a few years back in the 80's.

Bruce

What is a two level drain?

We just finished 86 straight hours below zero and we are building an ICF house.

I feel your subzero pain.  I am at about the same latitude, but it is in the 40's :-)

When you do an inverted roof, you have 6+ inches of extruded HD insulation (usually in 2" layers) plus 3-4" or more of concrete and/or pavers.  Styrofoam used for this purpose has the edges relieved around the bottom to facilitate drainage.

A 2 level drain has a flashing collar to receive the roofing membrane at the slab level and a "body" that is adjustable in height to support the grill at the finish paving level. 

Every time you enter a commercial office building where the building is set back from the property line and there is underground parking or plant space, you are probably walking on a system something like I have described.  Very normal in commercial buildings.

Bruce

If I have my say, a concrete roof would be Lite-Deck.