Why do chimneys leak more than other roof details?
A chimney is a large obstruction in the path of water, made of a different material that moves differently. Water from the roof runs into its uphill face, and flashing has to carry it around. When metal, mortar or sealant weaken, water has a direct path into the house, so chimneys are among the most common leak sources.
Freeze-thaw cycles exaggerate the problem in northern Illinois. Water in a small crack freezes and widens it, and the next thaw sends more water in.
Plan to have the chimney looked at whenever the roof is replaced, even if it seems fine.
Can I fix a chimney leak with sealant?
Temporarily, perhaps. Sealant is a short-term patch on a joint that was meant to be sealed by metal. It tends to dry and pull away within a few seasons, and it can hide a failing flashing. A durable repair re-flashes the chimney, with sealant as backup.
If a roofer proposes only a bead of sealant for a chimney that is leaking, ask why metal is not part of the repair. In some cases the flashing is sound and the sealant is the right answer, but that should be the result of an inspection.
How do a chimney's cap and crown affect roof leaks?
Water that enters through a cracked crown or missing cap runs down inside the chimney or through the masonry and can emerge as a stain on the ceiling that looks like a roof leak. Checking the top of the chimney is part of any chimney leak diagnosis, alongside the flashing at its base.
The crown is the sloped cement collar at the top of a masonry chimney. If it cracks, rain and snow enter the brick, freeze, and gradually loosen the mortar below. A cap over the flue stops rain and animals from entering the opening.
A roofer may inspect these from the roof and advise a mason to repair them. Ask for a clear statement of what is roofing and what is masonry, so you do not pay twice for diagnosing the same leak.
What is a chimney saddle and does mine need one?
A saddle, also called a cricket, is a small peaked structure behind a chimney that diverts water around it. Wide chimneys without one collect snow, leaves and meltwater on the uphill side. The roofer can tell whether yours needs one by its width and the pitch of the roof.
Saddles are usually made of wood and covered with metal or shingles. They are a modest addition when the roof is open, and harder to retrofit on a finished roof.
Who handles cracked mortar and a damaged crown?
A mason does. Roofers deal with flashing and shingles, while mortar joints, brick, and the cap or crown on top of the chimney are masonry. A good roofer will tell you where the boundary lies and coordinate with a mason if needed. Ask whether each quote includes the other trade.
Because water can enter through the masonry itself, a roof repair may not cure a chimney leak if the bricks and mortar are failing. Be ready for a two-stage fix.
