Hi,

I'm a little puzzled by the final steps in an instruction pamphlet for installation of Jeld-Wen aluminum windows. I'm trying to figure out why I would want a 3/8" gap (see below, copied from the instructions) between the window and the siding, and how the exterior trim is installed to seal and hide this gap. I haven't installed windows before. The rest of the house has 2x2 cedar trim around the windows. I'm a little uncomfortable with hoping it'll all make sense as I do the installation and would like to understand how this works before starting.

The windows have a slip-on nailing fin on the inside and another lip or fin on the exterior side of a j-channel. Should the trim cover this exterior fin?

The full instruction sheet is at JELD-WEN Windows and Doors | Installation and Finishing (New construction aluminum windows (pdf)).

Thanks!

Steve
From Jeld-Wen website at JELD-WEN Windows and Doors | Installation and Finishing (New construction aluminum windows (pdf)).

AFTER INSTALLATION
4. Install exterior wall surface within seven days of window
installation.
5. Maintain gap of 1/4"-3/8" between window frame and
fi nal exterior wall surface (siding, stucco, etc.).
6. Seal this gap on the sides and under the window sill with
backer rod and sealant. Do not apply sealant on top of
the drip cap
7. On the interior, insulate the void between the rough
opening and the window frame with loose-fill fiberglass
insulation. Do not use high-expansion foam.

 

The gap is to ensure that expansion and contraction does not exert any force on the window frame itself. The instructions are a way of ensuring that there is an expansion joint all the way around the perimeter of the window. IMO, 3/8" is way too much.

You didn't say what type of siding/exterior you have, and whether or not you plan on using some sort of trim around the windows... but usually what happens is you have a trim that covers the window nailing flange (2" wide brickmold is common) which you would want to leave spaced away from the window 1/4". (I prefer 1/8", but a larger gap allows backer rod behind the sealant which may result in a better, longer lasting expansion joint) Then your siding usually will have a small 1/8" gap where it butts into the brickmold.

Not sure if that answers your question or not?

 

The siding is 5/8" CDX plywood, which is also the sheathing. The window will be installed on the framing, then the siding will be installed.

Yes there will be trim. I guess you're saying he trim goes on before the siding, not over it.

The main source of confusion is that the nailing fin is set back about 5/8" from a second narrower "fin" (not sure that's what it's called) around the outside of the window, which leaves a gap between the two fins. In other words, the window will stick out appx. 5/8" from the framing.

I was thinking either the siding or the trim inserts into this gap. But after what you're telling me, the trim just goes up to the outer fin within 1/4"-1/2", then the siding goes on around the trim?

 

Usually that's the case, yes. But in tract housing, you often see them install the siding first, and then just nail some trim over the top "for looks". When its done that way, there is no drip cap, and you usually see the trim rotting off the house in a few years because water gets trapped behind the trim, rotting both the trim and the siding.

Question... can that outer fin be removed? Because for your installation, you really don't need it, and IMO it seems like it is creating a problem when you want to caulk the trim to the window. If it can't, no big deal. Read on.

It sounds to me like an integral j-channel. They are a real pain in the *** when you want to caulk the edge of the siding to the window.

Correct. Either the siding or the trim goes into the gap, but it should not be inserted so far that it is tight against the window. There has to be room for expansion and contraction.

But IMO, what you should do is forget about inserting ANYTHING into that 5/8" gap. Instead butt some 1" thick trim (or your cedar 2x2) up against it (maintain a 1/8" gap... or 1/4" gap if you want to follow their instructions to a "T". If your trim is at least 1" thick, that means your trim will protrude 3/8" past the front fin (your integral j-channel) and you will then have a nice place to run a bead of sealant around, sealing up the perimeter of the window.

You will want to install the window first, incorporating it into the housewrap, just as the instructions indicate... install a drip cap over the top piece of trim, then install your siding over the top of that.

You will need to ensure that you have sufficient framing around the window to do that, so that the edge of your siding will have some solid framing to nail to. Because otherwise, if your trim is very wide it will cover up the double stud on each side of the window and the edge of your siding won't have anything solid to nail to. Wide trim may require three or more studs on each side of the window.

If, years down the road, you ever have to remove the window, having trim (and not siding) over the nailing flange allows you to remove the trim and remove the window without having to tear out any of the siding to do it.