Is there a minimum realistic height for a window buck off of the decking that cannot be poured? 

A few of my windows are 6" off of the decking, and I am concerned with not being able to get enough concrete flow underneath.  Two of these windows are 6 feet wide, and one is nearly 9 feet wide.   My current thought is it would be better to stick frame underneath these windows instead.   Or would it be possible to hand place concrete in these areas with a wheelbarrow and shovel?

TIA -

The concrete could be placed with a wheelbarrow and shovel.  Depending on the width of the window and the size of the pump you might be able to place with the pump.  Make sure you use an internal vibrator to make sure you have consolidation under the window. 

Leave the sill out of your buck but have it ready to go in I usually use it as and additional spreader until I have filled below my windows, then I just tap it down into place and toe screw it to the sides of the buck, on a buck that long we also add a few pins to the sill so it is locked in.

What type of bucks do you use? We always use treated 2x materials for our bucks and use 2-2x4's on the bottom. These are flushed to the inside and outside of the side bucks, leaving a space in the center for installing the concrete. We pump concrete on either side of the window/door opening and let the concrete flow as far under the opening as it will, then finsih filling under the opening through the space between the 2x4's. It is not a problem using this method.

Several openings in the sill buck may not substantially effect its strength and would definately improve the pour by being able to add concrete from the middle. Just come up with a way to seal them effectively so that hydrostatic pressure can't force concrete up through the opening as you pour the surrounding walls. Be sure that you order windows with the proper safety glass in them for placing them low.

Mark Fleming

Or if you don't want to worry about the thin sills on pour day, hand mix and pour a "curb" and wet set your windows beforehand.

Kevin

If this is an ICF floor to floor, you can pour the 6" lift with the initial pour just by boxing it out accordingly. Why pour up to the level of the deck, then add 6" later? Assuming you are using one of the Simpson style ledger hangars!