In the process of researching new windows and installation, I came across the idea of sloping the framing sill in an effort to prevent water from entering the house. I like this idea, but am unclear as to some of the details when installing new construction windows (those with a nailing flange).

When using a sloped sill will it be necessary to place permanent shims between the window sill and the actual framing sill? Or will it be enough to allow the window to be support by the nailing flange?

Since I am leaning toward Simonton BrickMould 600, I have been reviewing their installation instructions. The Simonton instructions indicate that the window can be fully supported by only the nailing flange and does not rely on the window sill itself.

Thank you!