I’ve just finished installation of Andersen 400 Woodwright Series windows and am working on the casing (5″) which includes a sill “nosing” to approximate the original.
Since the windows were new construction and therefore included the plastic tabs that lay proud of the sheathing, I have rabbetted the interior opening of the casing approximately 1.5″.
The sill nosing is 1.625″ thick – only slightly wider than the tab itself. If I provide a through dado to accomodate the tab, this leaves a 0.125″ gap along the bottom length of the window underneath the sill nosing which I’m concerned will not be covered when the clapboards are installed.
The installation guidelines for the window call for a 0.250″ gap between the window and the casing to be filled with backer rod and caulk. As we all know, caulk fails.
Should I:
1) Keep the the gap underneath the sill nosing to let any water that infiltrates to escape?
or
2) Construct a jig for my router (sill is 12 degrees) to enable me to cut a rabbet in order that the bottom window tab will be covered and there will be no gap underneath the sill nosing?
Also, in this installation, isn’t it is expected that water will eventually make it behind the caulk surrounding the window and into the rabbets that cover the window tabs? Is it important to allow the water that accumulates to drain (e.g., through the gap behind the sill nosing) or will this just invite rot and/or insects?
Thanks!
Greg
Replies
I usually want the clapboard below the window to tuck behind the sill nosing, and that 1/8" gap isn't big enough for that. I would actually enlarge that gap by cutting a 1/4 rabbet along the bottom edge of the sill nosing, as well as a drip grove along the bottom of the sill nosing about 3/8" back from the front edge. I might caulk the vertical gaps, and not the bottom, but more likely I would not caulk any of them. But if you want warranty coverage, you probably ought to calk them...though any failure would probably long after the warranty period no matter what, so...
Steve
Excellent, Steve...thank you. I like the idea of the clapboard fitting into a rabbet underneath the sill. I can still rout out the area for the flange...
Greg
Mike Smith has done quite a few of those using Trex as the 'sill'.
Maybe we can scare him up.
Mike,
Look back a couple of posts.
I thought you might be able to help out here. I remember some posts of yours where I think you did the same thing.