Vinyl siding detail- windows/j-channel


Old 05-09-05, 08:30 AM
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Vinyl siding detail- windows/j-channel

Just reviewed the current emailed DIY newsletter re installing vinyl siding. I basically understand the use of the j-channel above the window to serve to catch and divert rainwater, snow etc from above. I have vinyl siding with j-channel above wood frame windows, and the previous owner used caulk between the j-channel and window frame. The window frame extends about 1/4 inch beyond the j-channel. As vinyl and wood expand/contract at different rates, this does not seem a proper way to seal this, if in fact it does need to be sealed. Ideally wouldn't you want a drip cap installed up under the siding and over the wood window frame? I don't see any type of vinyl siding product like this in the big box stores or any other? Can you advise?
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Old 05-09-05, 12:09 PM
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usually it right above the window.
if the previous owner used a rubber type caulking should be ok
Old 05-09-05, 03:39 PM
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Vinyl Siding

The purpose of the J channel is to hold in the siding. J Channel also goes on all sides of windows, doors, and in many other places. When applying any siding, drip caps should be installed above windows and doors. Usually when you see J channel caulked with no drip cap, it is a result of forgetting to install the drip cap, which is very very common, even by professionals. I kind of got lost with your big box store statement of something you do not find.
vinyl siding, J channel and drip edge are sold all over the country. Hope this helps. Good Luck
Old 05-09-05, 03:55 PM
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If your question is regarding "sealing" the window from water, that's something that is impossible to do with vinyl siding. All water has to to get behind your vinyl siding is follow gravity down to the bottom of the j-channel, where it then gets behind your siding. Dripcap or no dripcap, this is GOING to happen.

Regarding caulking the j-channel to the wood trim, that's most often done in an attempt to make the job look better- more "seamless". It really serves no purpose as far as keeping out water, since water gets behind the siding elsewhere.

As Jack pointed out, dripcaps should be installed over the exterior trim boards before the siding goes on. The dripcap needs to be flashed behind the building paper in order to be effective. When a person caulks around the j-channel, he cannot caulk along the top of the dripcap, or else he will trap water behind the siding on top.

If your house is fairly new, it's likely that your windows have nailing fins, the top of which should be properly flashed behind the building paper. Often, builders will install wood trim over the top of these nailing fins, and not worry about flashing it, assuming that since the window itself is flashed correctly, the trim is expendable and prone to leakage around the vinyl siding anyway.

It sounds like what your are describing is the norm for most builders nowadays.
Old 05-09-05, 04:41 PM
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Vinyl Siding

X Sleeoer is correct. Good Luck
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