Install Flashing Around a Chimney
LESLIE: Listening on WABC in Hamlin, Pennsylvania we’ve got Mike. How can we help?
MIKE: Well, I’m doing a little roof job but my call is about the flashing around the chimney. Most old flashing was done – sealed with tar or some resemblance of tar. And I’ve wondering should I do it with tar or should I use a new, you know, 30-year-old silicone.
TOM: Neither, actually. The original flashing that was sort of tarred in place, that’s probably on top of metal flashing. Now the proper way …
LESLIE: Do you think that tar is a repair?
TOM: Probably is. The proper way to flash a chimney is with a two-piece flashing system. You have base flashing and counter flashing. And Mike, the base flashing goes under the roofing shingles and up against the side of the chimney. And then the counter flashing is notched (ph) into the mortar joint and then it covers the base flashing. So the two of them work together as sort of a slip joint so if the roof expands and contracts, if the chimney sways with the wind it doesn’t break the joint. You follow me? And that’s what …
MIKE: I understand but what do I seal them together with?
TOM: Well, once they’re actually assembled, you don’t have to seal them with anything. They basically layer each other and the counter flashing protects the base flashing. So the water hits the chimney and then it runs down to the counter flashing that runs down to the base flashing that runs off the roof. And that’s the way a system works. And that is the correct, proper way to flash a chimney that’s been done for many, many years. What probably happened in the history of this chimney, at some point the flashing got loose, flashing broke. Whatever happened, a roofer came in there and tarred over the whole thing …
LESLIE: As a repair.
TOM: Yeah, sort of a stop gap measure. But you don’t have to do that. If it’s flashed correctly, you shouldn’t have to tar it.
Mike, thanks so much for calling us at 1-888-MONEY-PIT. 888-666-3974.