Fix a Leaking Brick Chimney
LESLIE: Joe in California is on the line with a leaky chimney. Tell us what’s going on.
JOE: Well, it’s an old one from the 60s, I believe, but it was beautifully built. It’s 15 foot wide and 2 stories up and I’m on the second story. But the water is going through the mortar coming in and it’s terrible. It’s like a waterfall in the wintertime.
TOM: So, you say that water is coming through the mortar. Do you know for a fact that it’s coming through in a particular place? Because, generally, when chimneys leak, there’s two areas that we concentrate on. The first is the very top of the chimney. And if it’s a masonry chimney, you probably have a clay flue liner. Is that correct?
JOE: Yes, it is.
TOM: Alright. And then so the space between the clay flue liner and the outside edge of the brick chimney, that has to have a concrete cap on it. And that should be sloped away from the flue liner to the outside edge. It can’t have any cracks or holes or gaps in it. And very often, you have to caulk it, if that does develop, around the flue liner, as well as through the cracks.
The second place that chimneys typically leak is at their intersection with roofs. And unfortunately, roofers have almost universally lost the skill set that would have enabled them to be able to flash this joint properly between the chimney and the roof. Because the proper way to do this is with a two-piece flashing system where you have a base flashing that goes underneath the roof shingle and up against the side of the chimney. Then counter flashing, which is carved into the mortar joint, folds over the outside edge of the chimney and also over the base flashing.
And the reason that sort of two-piece design is important is because chimneys are always moving and roofs are always moving and they don’t move together. And so, this is sort of a slip joint, so to speak, where they can actually move and shift with the wind and the heat and the rain and the expansion and contraction without actually breaking down.
So, I would look at those two areas. And then I’ll just give you one other tip. If you have a roof where there’s a lot of water running down before it hits the base of the chimney, in a situation like that, what you want to do is put a diverter on the roof, midway, to kind of short-circuit some of the water that’s running down towards the chimney and run it around the chimney. And that will just simply reduce the volume of water that’s getting in there and potentially leaking through into your house.
JOE: This has got a flat, metal top over the top of the chimney that mostly keeps the rain from coming down the chimney but I haven’t really looked at the flue liner up there. That’s a good point.
TOM: Yep. Take a careful look, Joe, OK?
JOE: OK. Alrighty. Thank you very much.
TOM: Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.