I am trying to determine the best way to address a vinyl siding leak adjacent to a patio door. Water is somehow working its way behind the vinyl. The door has J-channel on top and sides; the flaps on the top piece seem to properly lap over the side pieces. Water going into the top J-channel all runs to the side where the leak is. The siding is fairly snug against the inside wall of the J on that side of the patio door. I believe water rounding the bend from the top and running down the side channel is being diverted behind the siding due to the tight fit. I also feel, however, that this would not happen if the top had drip cap instead of J-channel. I realize J-channel is commonly used at the top, but it seems to beg for this sort of problem.
Jim it sounds to me like the door is not properly flashed or the J channel is not properly installed. Flashing needs to be installed on both the sides and the top of the door. The top piece of J-channel should have been cut long and the tab bent down over the side J-channel to flash the corner of the door and prevent water penetration.
You can get more details on correct vinyl siding installation details at the link shown below
The Cabo Code (at least the NC version) and perhaps others do not require house wrap or tar paper behind the vinyl. Some manufacturers do not want tar paper there because the black stain leaches out of the weep holes. I use Amocore P38 with taped joints, and I agree that the idea of using J channel everywhere is a mistake. Drip cap flashing and a starter strip would be very nice in this instance.
Our approach is that all siding leaks. THe flashing of the door is a separate issue from the installation of the siding. With vinyl siding we use Tyvek's window wrap over the top flange & under the tarpaper or housewrap above.
Also check to see if anything higher up the wall is letting water get behind the siding.