Proper Chimney Flashing
LESLIE: Dan in Michigan, you’ve got The Money Pit. How can we help you today?
DAN: Hi there. I have a question for you. I have recently purchased a 1920s home.
TOM: Thank you for personally pulling us out of the recession, Dan.
DAN: Do what I can.
TOM: So what’s going on with this beautiful 1920s home?
DAN: Well, we’re in the process of making it beautiful but I have an upstairs ceiling that has a wet spot and it kind of scuttle-holed it up there, to see what’s going on up there, and the chimney is dripping.
DAN: And so I got up on the roof and the flashing appears to be fine. And the chimney was – the way they laid the bricks up, they kind of stuffed them and I’m wondering if the mortar is compromised and maybe that brick is leaking.
TOM: Well, if you’ve already been up on the roof, what I would do is I would – and you think the flashing is fine – I would take a hose and run it around the flashing itself, because I suspect the flashing is not fine. A lot of times the roofers will cut corners with chimney flashing.
The proper way to do this is to have two pieces: a base flashing and a counter flashing. The base flashing goes under the shingles and lays up against the side of the chimney; the counter flashing gets notched into the mortar joint and then folds over the base flashing. So that kind of works together. And the reason you have two pieces like that is because you’re going to get a lot of movement – expansion and contraction – and it doesn’t pull the flashing away.
Another thing to check is up on top of the chimney: the concrete cap that’s going to be between the flue liner and the end of the brick. Make sure that that’s solid. Very often it will crack and you’ll need to caulk it or fill gaps in around there.
And the third thing that you could do is you could use a masonry sealer on that brick and that will slow down the absorption of it. You want to make sure you choose one that’s vapor-permeable so that the moisture can get in and get out of the brick. And this will prevent the possibility of it freezing and spalling or breaking up in the wintertime.
DAN: OK. Vapor-permeable.
TOM: Vapor-permeable, yep. Most of them are today. Just double-check.
DAN: Alright. Very good. I appreciate that.
TOM: Good luck, Dan. Thanks so much for calling us at 888-MONEY-PIT.