How to measure for precast window sills

What a window sill needs to do

A precast window sill sits under the window opening and carries water away from the wall. To do that well it needs the right length to span the opening with an overhang on each side, enough depth to project past the wall face, and a slight slope so water runs off rather than pooling.

The measurements to take

• Length: measure the full width of the rough opening, then add an overhang on each side. The sill should run past the opening so water sheds clear of the jambs.
• Depth: measure from the window frame out to the wall face, then add the projection you want the sill to stick out past the wall.
• Wall thickness: note the finished wall thickness, including any veneer, so the sill seats correctly.
• Quantity and handing: count your openings and note any that are a different size, so we can group identical sills and flag the one-offs.

Stock widths vs. custom

We stock precast sills in a full range of widths, sorted by size, so many openings are covered by a standard size. If your opening falls between sizes or needs a special length, our mold shop casts custom sills and lintels to your exact dimensions. When in doubt, send us your measurements and we will confirm the right sill before anything is cast.