Good read about ICF window buck area weatherproofing test and study from ICF Magazine

The best module during testing was when the window was attached directly to the concrete area with NO wood buck:

Module #4: Window Sealed Directly to Concrete

Rough Opening
In the fourth sample, the buck was stripped after the pour, leaving the concrete core exposed. This method is common to commercial and multi-family multi-story buildings of any height. A box-framed (equal leg) window was positioned at the exterior face of the concrete core. Both the interior and exterior face of the window were sealed with foam backer-rod and silicone sealant directly to the concrete core.

Since the concrete core is providing 100% protection, no exterior window flashing was required.

This assembly was by far the most successful at resisting water and air infiltration. After having successfully resisted pressures in laboratory testing of 104.42 psf [5000 Pa]. the field test module was successful in resisting air and water infiltration up to pressures of 14.62 psf [700 Pa]. This is extraordinary. This is equivalent to wind speeds of more than 500 mph, conditions that don’t even exist on this planet (maybe Jupiter), and the ICF wall/window assembly was proven 100% tight in such conditions. In the opinion of the author, this is a game-changer.

MODULE #4 DETAIL

If one is concerned about thermal bridging with the above detail. A simple solution would be to take 2" of rigid EPS and glue/screw it so that it abuts and insulates the window frame on the top and bottom. Then on the inside of the home, do the same. That way the window frame is insulated with 4" of EPS and it stops any thermal bridging.

Easy to do.

Good read....also seems harder to finish on exterior and interior for drywall/trim.

Why would this be better then Nudura end caps and lintel bucks? Or any ICF product with dove tailed backs and mounting webs case into the foam?
Module four may provide low infiltration but it provides high thermal transfer.

Crap, well I built my ICF home on Jupiter and I used LOGIX Pro Bucks. I'm screwed.

Yeah I'd go with ICF bucks instead of raw attachment to concrete - with raw attachment, if you ever need to replace the frame, it will be a PITA. You'll be tearing out foam if you added it extra for the thermal bridging, and the drywall\jamb\trim if you take the frame out from the inside.

LBear, great article but is it realistic to think that 1) the EPS will not need to be protected with some kind of final veneer (siding, brick, stone, etc) which will create a need for proper flashing and weather/waterproofing? 2) will code compliance inspectors allow no primary/secondary barrier over the EPS exterior? 3) what is to prevent water from entering the EPS between the bottom of the window (will) and the space between EPS and concrete core?
Are the windows attached directly to the concrete with some sort of Tapcons or pre-installed anchors?
From the article:
Exterior Moisture Protection
U.S. and Canadian building codes typically call for a primary weather barrier (such as siding or stucco) and a secondary weather barrier (such as building paper or other synthetic membrane) behind it. This is because wood-framed walls must be kept dry to protect them from moisture damage.

Both codes contain exemptions from the secondary weather barrier in the case of above-grade masonry or concrete walls, which are recognized as a watertight plane and shed water adequately on their own.

Exterior Insulation
The expanded polystyrene (EPS) used in ICFs will not allow the passage of water or water vapor through the EPS panel, but the joints (horizontal and vertical) between ICF units can allow the passage of water, driven either by wind or gravity. This is an apparent conflict with building codes that typically require the exterior building shell to be able to shed water to the outermost plane of the wall, where it can’t harm wood framing. Not able to see concrete behind the ICF outer insulation, building officials often default to conventional wood-framed construction requirements, and expect a membrane between the building sheathing and the exterior cladding.
This is not only unnecessary, but is also unpopular among ICF proponents who object to the added costs.
What would the flashing look like using Module #4 with brick veneer?