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Question DetailsAsked on 5/3/2014

vinal siding just installed should windows be chalked where siding meets?

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5 Answers


With vinyl siding and actually most sidings caulk is not really needed if the flashings and trim is installed correctly. Sadly in todays world many are taking short cuts or are in the business without knowing the proper ways. Your vinyl siding will expand and contract with the changing seasons and even just the fluctuation in the day's sun exposure and temp. I have seen some areas where for some reason no J channel trim was used around the windows and doors and caulk was used instead and the water damage was major. I saw it in whole subdivisions and the only thing I could think of as either since from the age of the houses vinyl siding was a new product and they did not know any better or they were just saving money.

Almost all caulking will fail with exposure to the elements and the best protection is proper insallation. You should have J channel around the window and doors and it should be cut with tabs that direct the water from the top down the sides and out the bottom. And if a small amout should get behind the siding the house wrap should take care of it. Caulking this channel will actually make water easier as it can cause a backup of water that could possibly run behind the siding.

The proper installation is where you will see a difference in pricing on jobs. I generally will not install viny when the temp is below 20 degrees as it is hard to bend the tabs around the tops and under the bottom of windows or doors. If I must to finish a job I will heat the trim with a heat gun to soften the material , but that is only if this is the final thing to do on and addition or house. If you see siding being done when it is this cold odds are they are not doing this unless you see a torch on the work bench.

So I guess I may have given you a longer answer than you wanted. But no if properly applied it is not used.


Answered 6 years ago by ContractorDon


Absolutely yes - J channel (the aluminum strip that the siding slots into at the windows) basically just funnels the water down behind the siding, and should be the second line of defense, not the first.

However, realize aluminum siding moves a lot with temperature changes, so caulking the ends is a continuing chore - at least yearly, and probably more often than than.

Answered 6 years ago by LCD


Don made a good point - if caulking (which I definitely recommend if you made the mistake of getting vinyl or metal plank siding), then you should only caulk wherethe board interfaces into the J channel - NOT fillin the J channel with caulk, and NEVER caulking where the J-channel bottom tab comes out on top of a plank at tehbtoom of the window frame corner, because that is where any water in the channel drains out.

There are also specific foam seals and press-in soft caulk tubing that press into that junction to seal the plannkk tothe J channel - some appear to work, some not so much.

Answered 6 years ago by LCD


The caulking if done according to industry standards should actually not be seen. If it is an older house with existing windows flashing should be installed to the window prior to J channel being installed and it is the flashing that should be bedded in caulk. The flashing if done correctly directs the water away as well as the proper installation of the J channel. Caulking this area (the J channel) can actually cause water to build up and cause leaks behind the siding. I have had to do quite a few repairs due to this and it is even worse when caulk was applied to J channel applied to a dormer along a roof. Once caulk has been apllied to the junction of a corner post or J channel it will fail and it is next to impossible to dig it out and replace it even though it should not have been there in the first place.

You can Google "Vinyl siding installation instructions" and you will find a manual put out by the Vinyl Siding Institute. It is a bit hard to understand the proper placing of caulk fron the diagrams unless you are in the trade and know the window parts but it might give you an idea.

Caulk is used on sidings such as Hardi board or wood clapboard at corners or windows and Hardi will actually send out representatives to check on details such as this before they give the extended warranty on their product.


Answered 6 years ago by ContractorDon


Don's point is well taken, and illustrates a major basic flaw of metal and plastic siding - the manufacturers have totally failed to come up with a meaningful end sealing method, like an encapsulating rubber gaspet strip that would fit inside the J-channel and around the end of the planks.

This article shows typical J channel -

and the lower right photo shows clearly how, without caulk or sealer of some type, the water can blow or sometimes just flow off the J channel under the siding. It would be nice if it flowed down the channel and out the bottom like the manufacturer diagrams show - but in the real world it commonly does not. Commonly it just flows off the flat side of the J channel or through the nailing slots onto the housewrap, then flows all the way down the wall under the siding till it (hopefully) drips out under the siding - a VERY poor design, to say the least, as it really makes the housewrap or felt the primary protection layer, which it is not designed to be. You can see in the photo in this blog -

how the J channel does nothing to keep the water from flowing off its side, away from the window or door or corner and onto the housewrap, under the siding and wetting the wall interior. This is not limited to J channel either - flat flashing liek around chimneys does exactly the same thing - actually promotes water flowing in under shingles, rather than directing it along the flashing to a surface exit point by blocking its movement to the free edge. With flexible (asphalt) shingles this can be avoid by creating a rolled-back edge on the flashing like this "tile pan" or "J-pan" flashing -

or by running heavy sealant or caulk down the free edge of the flashing before putting on the shingles to prevent the water from flowiong off the side of flashing - almost no contractors take this trouble. However, with profiled siding, this does not work - though I have used self-adhesive soft foam backer along the free edge of the J-channel strip to reduce the possibility of this in the past, but it is easy to damage while slipping the plank into the J-channel.

Someday, after a major defective product lawsuit, manufacturers will address this issue by curling the free edge of the J channel to actually contain the water in the channel.

Answered 6 years ago by LCD

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