Install Window Trim Over Siding

Building paper is an important part of the wall s waterproofing.

Install window trim over siding.

In order to get the most accurate cut line we decided to place our new window in the opening to trace it. Face nail trims using 2 inch 16 gauge finish nails after every 16 inches apart. The cement board panels are fastened to the battens. Touch up the divided hardie trim boards before trimming them to your window.

Slide the top edge under the window fin then nail off the fin with roofing nails. Before you replace the siding cut and install new j channels to prevent water from leaking into your home. We used pressure treated 2 x 4 s for the trim around the windows and the doorway and then we had to create trim corners for both the inside and the outside corners like the ones in the picture above. The rain screen battens are run down to the top of the window flange.

If the trim is being applied over the hardi panels. The wrb is lapped over the head flashing or the flashing is taped. Level and tack the new window in place then cut a piece of aluminum flashing to width so it extends from the new window to overlap the nailing hem of the siding below. This meant our new windows would have trim that was much wider than our old windows making it necessary to cut away a bit of our siding to sit flush with the edge of that new trim.

If we installed the trim after the siding we would have had to caulk a ton to fill in for the different levels the layered siding creates. Cut the horizontal piece to size and snap it in place over the vertical moldings. The head flashing is installed in a bed of caulking onto the top of the window frame.