The wall thickness was already customisable with three options, but from today on the rendering actually shows the window sills with a real depth. No more need to trick it with "fake" walls to create this effect in your design.
This new approach is default for all your new rooms. No old rooms will be changed automatically, but you can apply the effect by remixing and requesting a new render of it.
Give it a try when designing your next masterpiece, and let us know what you think.