Install flashing on existing roof


I have a leak where my porch roof attaches to the side of the house. I’ve seen it drip twice, both times in a storm when the wind is blowing hard (normal rains there seems to be no drip coming through). I have not been up on the roof yet to check, by my guess is that the guy who flipped the house did a terrible job on flashing (or didn’t install it at all) when he put a new roof on the house. House has vinyl siding.

Question: Can I install flashing or some type of protective barrier without tearing the shingles off the roof, and starting over? If so, how?

Thanks for any and all advice!


We need some pictures of the area you are talking about.


The guy who did this bent down the j-channel and filled with caulking (and did a terrible job of caulking) between the j-channel and shingles.

Here is an image.


Is that aluminum or vinyl siding? It looks like they just butted the shingles to the siding and caulked. The proper way to flash that is to remove the bottom pieces of siding, install step flashings under every course of shingles that goes behind the siding, then reinstall the siding. If it is vinyl siding it is not too difficult, if it’s aluminum it’s a much bigger pita. Burrying the j channel in the shingles is going to leak, it needs to be on top of the shingles. Was the old roof torn off?


The j-channel is aluminum, but siding is vinyl. What you describe is dead on. The moron tore off the old shingles, put new on and didn’t put any flashing—even I knew to do that!!! My question is how do I get this step flashing under the shingles? Do I have to tear off the roof, or can I pry up the current shingles? Thanks again for the help!


You should be able to carefully remove the shingles and install your step flashings. The seal on arch. shingles can be a bear when it’s hot out. Try lays a bag of ice on them for a bit and then break the seal with a flatbar. Good luck!


Thanks for the reply and the tip on separating shingles. Guessing I should replace the j-channel while I’m up there?


Be kinda silly not to, that alum. J looks to be flattened out some. Be easier to just get some new vinyl J.


Yes…the guy who did this bang up roofing job flattened the j-channel against the shingles and then put caulking between. Thanks again for the advice!