To help prevent leaks, I was advised by a contractor that I need to caulk where my vinyl siding meets the edges of my windows. Some research of my own reveals quite a bit of debate over this, a few saying that the caulking will wear out fast because of the expansion/contraction of the siding. Others say that, if the vinyl is installed properly, caulking is a superfluous measure of protection. I am wondering what SE has to say on the matter.

3 Answers 3


Agreed with the research you found. Most vinyl siding, if installed correctly, will not require caulk at the sides of the windows and doors. Often there is actually a separate vinyl piece installed first at the side of the window that the ends of the siding tuck into. You are supposed to leave a gap at the end of the siding pieces to permit expansion and contraction. This same siding movement is the reason that the siding comes with slotted nail holes.

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(from the familyhandyman.com web site)

  • Agreed. The vinyl around the windows is referred to as J-channel. It gets installed from bottom up so that all the overlapped edges channel water away from the home.
    – BMitch
    Commented Dec 16, 2014 at 14:15

Vinyl siding DOES NOT keep water on its front side. NO caulk or installation manner will modify the fact that water gets behind vinyl siding at many seams. This is especially true above every window and door. Inside corners can also intake a lot of water given correct wind.

Vinyl siding is not now, and never was, a means of keeping water away from a home. Vinyl siding protects the water barrier which must be properly installed behind it from harshness. Vinyl siding allows fragile house wrap to function as the moisture barrier, keeping all water outside of the house for many years.

1) House wrap must be installed from the bottom up (overlapping like shingles so that upper water flows onto the outside of the lower sheet). 2) Caulking must be placed between the layers of house wrap at all vertical seams. 3) Caulking must exist between the house wrap and the windows. New construction allows the house wrap to be folded around the rough opening, making it easier to create a water tight seam between the window and the house wrap. In a remodeling situation, caulking should be placed between the house wrap the the new aluminum window wrappings. Caulking can be placed behind the J-Channel during installation, sealing the seam between the J-Channel and the house wrap, also sealing the seam between the J-Channel and the window itself.

Many vinyl siding installers do not realize the importance of the house wrap (and its job as the sole water barrier) because many people incorrectly believe that vinyl siding keeps the water out. Vinyl siding only protects a water barrier from direct weather abuse (driving rain, wind, sun, sand, etc.).

You want the easiest solution. Considering its design, vinyl siding does very well. Although the problem is likely whole house, the worst spots are localized due to wind direction. 1) Take the siding down. 2) Water proof the house. 3) Put the siding back.

  • 1
    I agree with your "simple fact": vinyl siding does not keep moisture out and I like your 1) lapping and sealing the laps of all types of housewrap. Where I live, water flows "up" due to wind pressure. However, we've learned that moisture needs to "get out". That's why we don't caulk the head of windows and doors...we use window tape and seal the frame to the housewrap. But we caulk the jambs and sills...
    – Lee Sam
    Commented Jul 28, 2017 at 2:13

This sounds like bad advice from the contractor, but it's possible there's a specific problem we can't see over the internet.

Typically, to prevent leaks around windows, the window itself is sealed to the house wrap, often with a self sticking rubber flashing. That sort of flashing is installed from the bottom up to ensure all overlaps channel water away from the structure. This is the procedure for new construction windows, so there may be somewhere to caulk around replacement windows.

For air leaks, you need weather stripping around the moving parts of the window, and insulation between the window and frame (often minimal-expanding foam designed specifically for windows and doors).

Vinyl siding is expected to have some water get behind it so there's nothing to waterproof between the siding and the structure. It should hang loose for expansion/contraction but also overlap to minimize the amount of water that gets behind it.

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