Revisions log for Answer #1089

I'm not an expert, but the design in the old house seems better to me. In my house (not new construction) it is also the case that the shutter guide rails end just before the window sills (as in your right picture). As in the left picture, I would be worried that the last slat of the shutters might be at the bottom. Some air is necessary in my opinion (water drainage, expansion in heat), but not more than 5 – 10 mm. I can't estimate it well from the photo, but I think it's more in your case (2-3 cm?).