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I am removing the punky exterior casing trim and part of the sill of a window that a woodpecker attacked.

punky window casing

There is a vertical piece of wood about 3/4 x 1 on left and right partially below the casing trim:

frame piece with groove

I've removed the trim and those two pieces. Here's the one from the right side of the window; you can see the white primer which was hidden behind the casing trim and not painted:

wooden piece removed from window

These two vertical pieces have a small channel routed into their inside face.

groove on inner face

I need to replace those pieces because they're punky near the sill and the woodpecker destroyed the bottom section of the one on the right side of the window. Is that channel on the back side to let moisture drip down to the sill?

Here's a picture of the window with the casing trim and that strip of wood removed:

casing trim removed

The top of the groove would be right where the mitered-corner of the casing trim would channel water.

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  • You probably mean "funky", unless your window listens to the Sex Pistols. Anyway I don't think the channels are for water. There should be no water running down the inside parts of a window frame. My guess is this is a replacement window (mainly by the different colors of the framing) and the trim's channel mated with some part of the original window but not with this new one.
    – jay613
    Commented May 25, 2022 at 18:28
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    It was actually a new window put into a room that was added over the garage. And the adjective punky means soft and rotting ... at least when it comes to wood. merriam-webster.com/dictionary/punky
    – mr blint
    Commented May 25, 2022 at 19:10
  • Well I may be wrong on both points then. If the window in the picture was the original window when that opening was cut out of the wall, maybe the groove served no purpose and it's just what the carpenter had.
    – jay613
    Commented May 26, 2022 at 13:42
  • I've seen grooves like that milled into the back side of door jamb kits. They seem to serve no purpose that I've ever been able to identify. If it were for an aircraft, race car or bike, I'd suggest "lightening without reducing strength", that doesn't really apply to house construction.
    – FreeMan
    Commented May 26, 2022 at 15:21

1 Answer 1

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I can't get my head around where the channel was in the installation, but common purposes for such channels are:

  • Engagement of accessory extension jambs, used to extend for brickwork, for example. The same tend to be found inside to allow conversion of 2x4 depth windows to fit 2x6 walls.
  • Insect screen retention, many of which are installed via side springs.
  • Simple modularity across a manufacturer's product line. There are a zillion different wooden parts milled at window factories (I've toured Andersen), and any cross-compatibility saves cost.
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  • Could be your final point is the explanation. That channel is on the inner face of the strip of wood and it "mates" with nothing. That is what puzzled me. The strip of wood is nailed, channel facing in, to the flat-faced yellowish strip of wood in the final picture. That picture shows, moving from right-to-left, the cedar siding, the house-wrap, a gap with some insulation, the yellowish flat-faced strip of wood with nail-holes in it to which the strip with the channel was nailed, a vinyl piece into which the strip of wood with the channel nested slightly, and then the window sash.
    – mr blint
    Commented May 26, 2022 at 10:11

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