Keeping Weather and Wildlife Out of a Wallsburg Flue

Why so many flues here are open

Caps were never standard on older construction, and plenty of chimneys in this valley have been standing uncapped since they were built. Nothing dramatic happens for years, which is precisely why it gets left. What is happening is slow: rain and snow fall straight down the flue, soak into the smoke chamber and the masonry around it, and freeze there. Every cycle opens the joints slightly more. Add wind driving weather sideways along the canyon corridor and the exposed faces take it too.

By the time somebody notices, it presents as a damp patch on a bedroom ceiling near the chimney breast, or a white bloom of efflorescence on the brick, or mortar you can rake out with a finger. All three are the same story told late.

Animals, on open country

A warm dark shaft in open farmland attracts everything. Birds nest in flues in spring, raccoons will get into an open chimney and raise young in the smoke shelf, and wasps build in vent hoods and cap enclosures over the summer. A nest is a blockage, and a blockage means smoke or combustion gases coming back into the house. A cap with the right mesh keeps all of it out and costs a fraction of removing a nest and repairing what it caused.

The damper worth talking about

Old cast-iron throat dampers seal poorly even when they are working, and after decades of heat they typically do not close flush at all. That means the house is venting heated air up an open chimney every hour of the winter, whether or not there is a fire in it. A top-sealing damper mounts at the crown with a silicone gasket, closes the flue at the top rather than the throat, and doubles as a cap. On an older house that leaks heat through the chimney all winter, it is one of the few hearth products that genuinely pays for itself.

Snow is the other half of the water problem. Wallsburg sits high and cold enough that a roof holds snow for months rather than days, so the top of a chimney spends most of the winter with meltwater running over it through the afternoon and freezing again after dark, in the same places, over and over. A cap keeps that water out of the flue opening. It does nothing at all for a crown that is already cracked beneath it, which is why we look at the two together rather than fitting a lid and leaving.

Waterproofing that does not trap moisture

Once the top is protected, the exposed masonry can be treated. This has to be a breathable siloxane repellent, not a sealer that forms a film. Masonry needs to release moisture outward. Seal the surface and any water already inside is trapped, and in a valley that freezes hard overnight that trapped water is what pops the brick faces off.