I personally feel that sloping and flashing of the sill rough framing is a more important detail than the integrated sill of the window. Water doesnt behave like you tell it to in a diagram. The profiles pictured dont account for what happens in the corners, the seal between glass and frame or most egregious getting past the head and side nailing fins. From my experience, very little water makes it through the crack between the bottom sill of the casement and a picture framed trim piece. What little water does make it past is prevented from getting to the sill by the nailing fin and runs behind the siding on the weather resistive barrier WRB (housewrap). If this is a major concern then flashing tape over the second lap below should redirect it to outside the siding (second lap course because the first course is butted to the trim). I feel the amount of water involved here would be measured in drips per x gallons. I shot this pic this morning and know its hardly evidence but I may satisfy my curiosity a little more with some other methods on a project we currently have in the framing stage. My thoughts are to place some paper towels behind the picture framed piece, vigorously wet the window with 5 to 10 gallons and seeing how wet or if there is a measurable amount of moisture is getting through this admittedly vulnerable location (from a stand point of water behind cladding NOT rotting the sill). I dont think it will be much and feel that a sloping/flashed rough sill will handle the much more dangerous and damaging leak points.

We had a similar decision to make except that the casements were to open into a screened porch and we were concerned that while on the porch, people might run into them. We have double hung windows with grills on the top half all throughtout our home but I didn't want my sink centered on a middle piece of wood between two casements. Was just something I didn't personally like for our kitchen. We then saw a similar window to what is in my most recent post which has sliders where the side casements usually are and a large picture window in the middle. WE LOVE IT because it gives us unobstructed view, still has the venting options, screens are on the outside and we felt that having the option of the grills on the side windows, helped it to look more traditional like the rest of the windows in our home....our window is one of the best choices we made - we just love it! I copied my link to my pictures below....you'll see it in the 4th pic down over the sink. Here is a link that might be useful: imlebby's kitchen

One issue with wide casements--they swing well into outside walkpaths, etc. if those run alongside of the house outside the installation. Recently found myself almost braining myself when watering a flowerpot below an open kitchen window. We had to remove casements from our plan for lobby area when we realized they might smack close-by vehicles, bikes, etc. and would crowd the people who walk around a vehicle. Ended up with high awning windows, but could have done slide-by or double hung, I suppose. But by then I had thought hard about what a driveway view would be like and decided I wouldn't miss it.

Good thoughts from all. Unless historical or style mandate it when choosing windows, select tilt and turn, casements and swinging doors over double hungs and sliders. Regardless of which operation you choose, take a close look at how many operable windows are being specified. Egress and ventilation are often addressed with a single window which means the majority of windows can be fixed or inoperable. Fixed windows have the lowest upfront costs, energy and maintenance concerns and they allow the most view and light with thinner frames. Double hungs and sliders typically have leakier weatherstripping that wears out faster than swinging type windows and doors. Double hungs have more frame area which means poorer thermal performance (center of glass is better insulated than edge). How windows look from the exterior is obviously important, but I'm also interested in how they look from the inside. It drives me nuts to have a horizontal division in the middle of a double hung window, viewing out from in. Double hungs have only half the egress and ventilation area compared to casement, awning and tilt and turn. Cracking open a casement window should provide plenty of ventilation on a windy site without becoming a problem . A windy site would benefit even more from the better airtight characteristics of casement, awning and tilt/turn compared to double hungs and sliders.