What Is Undersill in Siding

The undersill trim is installed under every window above the ground line. It conceals the top edge of the vinyl siding and is also used at the soffit line.

Should I put foam board behind my vinyl siding?

Basically, in order to get a good insulation value out of foam board, it has to installed directly on the sheathing of the house. … Basically, if you want extra R-value for your walls but do not want to tear off your siding, don’t bother with the foam board.

What is vinyl utility trim?

Utility Trim: a piece of trim used any time the top lock has been removed from the siding, to secure a siding panel. Also referred to as “undersill” or “finish” trim; double utility trim is also available.