Install Window Trim Over Siding

Touch up the divided hardie trim boards before trimming them to your window.

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. Before you replace the siding cut and install new j channels to prevent water from leaking into your home. 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. Building paper is an important part of the wall s waterproofing.

Make sure that a drip cap is installed first over the window before going for the hardie siding. Cut the horizontal piece to size and snap it in place over the vertical moldings. 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. You will see the trims lay nice and flat.

Slide the top edge under the window fin then nail off the fin with roofing nails. If the trim is being applied over the hardi panels. Face nail trims using 2 inch 16 gauge finish nails after every 16 inches apart. Here is one great way to trim out a window or door opening with aluminum coil when using progressive foam insulation for plank style sidings such as fiber ce.

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. The head flashing is installed in a bed of caulking onto the top of the window frame.