So I'm over at Logix's website and I come across this neat little window detail:

 http://www.logixicf.com/media/cad/5_9_2-Rev498f9027358a7.pdf

I've noticed that many if not most form companies recommend window bucks with an open bottom so that the area beneath windows can be filled and consolidated directly and then capped. If one were integrating a poured in place concrete window sill like the Logix detail, would one need to cap it off? Is the hydraulic pressure of the fresh concrete not sufficient to push concrete up and out of the open-bottomed buck during the pour? If the wet concrete is stiff enough to remain in place, why isn't everyone doing their windows like this? The form and trowel work required appear trivial.

yours/
peter.

I have not poured an ICF wall in which the concrete did not come up and out of the bottom of the windows. That's why we cap them. I suppose that, if you were very carefull about how you pour the areas around the windows, giving the concrete some time to set before adding more around the windows, you might be able to control this. However, I would be afraid that minor bulging would still occur, causing more problems for the window installers.

Wes,

Thanks for such a succinct, informative answer.

yours/
peter.

we use horizontal 2x4's a the bottom of window opening to spread the vertical (temporary) bucks apart (which always get removed with stucco window wrap-arounds). then we pour the concrete flush to the top. the inside 2x4 (pt) is left in place as dry wall nailer. outside one can be discarded, which leaves a nice concrete sill ledge for the window flange to fit over. then we stucco a sloped window sill and any drip edge overhangs if needed.
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agreed with wes.

Just as an update to this post, my ICF installer wanted to try this and it seems we were successful. He essentially poured in three lifts with the first one about a foot higher than the bottom of the window sills. The concrete specs were 4000psi with 3/8ths aggregate and a slump of 5. Wall height was 9'2". Block was Logix 6.25".

Cheers/
Peter.

That is an interesting detail. But I don't think I would do it here, in the north-land.

Re: Window Detail: I prefer to run the exterior ICF foam all the way up under the window -- without it the wood provides quite the thermal bridge (more so in the north-land - ). Overall, when you consider that one can polish and stain the sills and round the corners etc. etc. this approach works quite well.

You have to watch things quite carefully, depending on slump (as mentioned above by wes) -- doing windows this way is outside of the typical installation and requires significant attention (and touch up) to the window sill(s)  for an hour or more after the pour is complete. Regards.

Seems like you could do that detail by filling the wall to just above sill level, top off the sill and cap it with a board and then fill the wall the rest of the way. Remove the cap after it's firmed up and won't rise but while it can still be finished.