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Hi,

I am replacing a few windows in my home and am wondering which parts of the exterior to caulk. The replacement windows are vinyl and are being installed in the existing openings. After the windows are installed the existing exterior trim on all 4 sides is being covered with new aluminum trim coil.

The trim coil is being bent to shape around the existing trim so that part of the new trim will overlap the replacement window and also bent to make a return around the trim to slip between the existing trim and the existing vinyl J-channel of the siding.

Should all 4 sides of the vinyl window to aluminum trim interface be caulked? Should all 4 sides of the aluminum trim to vinyl siding/J-channel interface be caulked?

I've read a few different opinions and the prevailing one seems to be that only the vinyl window to aluminum trim interface should be caulked. The thinking seems to be the caulking the aluminum trim to the siding J-channel wouldn't be necessary because the siding isn't watertight anyway and caulking that joint may even be detrimental because water could get trapped in that space. I appreciate any input. Thanks.

 

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Naildriver
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IF your windows are installed using nailing fins, they should be covered with 6" wide to fit window tape, then the trim installed then the coil. The tape should be installed bottom, sides, then top to keep the flow of water shedding off.
 

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Existing openings = a retrofit install. I don't typically caulk aluminum cladding to the vinyl j-channel because the vinyl isn't water tight anyway. But if it looks like caulking it would look better and keep water from getting behind the cladding in the first place, then I would caulk it.

Vulkem is a good one to use, it stays pliable. Quad sticks to vinyl the best, but its quite permanent.
 

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The best way. Is wrap the window sill first.
Install replacement window. Then caulk all around the window. And the wrapped sill plate where it meets the brick molding. At this stage make it water and air tight. And so no water can ever get under the sill plate wrapping.
For the rest it depends on if I can install a good drip cap. Since you have to expect water under vinyl siding.
If water can get under the trim wrap then no caulk so it does not get trapped.

With a drip cap I would caulk for cosmetic reasons, where the top and side trims meet the window.
 

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Replacement windows install against an exterior stop. Either the window is installed from inside against the stop or the stop is removed, the window is installed from outside and a new stop is installed against it. I caulk the stop before putting the window in place if inside installed or caulk the window and install the stop for an outside install. Then the caulk is sandwiched between the stop and the window. Then trim the opening. The caulk won’t show and if you want to you can add a fine bead at the trim/window intersection.
 
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