Keeping Water Out of Spanish Fork Chimneys

Wind finds the weak fastener

A chimney cap lives in the most punished position on the building. Here it also spends much of the winter being worked by sustained wind coming down the canyon, which is a different load from an occasional storm gust. Sustained wind loosens screws, fatigues thin sheet metal at the fold lines, and lifts caps that were friction-fitted rather than properly fastened. We pull caps off roofs in this town every year that were installed correctly for a calmer place.

The fix is not exotic. Stainless or heavy-gauge aluminum, mechanically fastened rather than pressed on, with a mesh that is sized for spark containment and animal exclusion rather than whatever came in the box. It costs slightly more once and then stops being a subject.

What a cap is actually preventing

Rain and snowmelt going straight down an open flue, which is how the damper rusts solid and how the firebox gets a smell in the spring. Birds and squirrels nesting in a warm vertical shaft, which is a real blockage risk and a real fire risk. Embers landing on a roof. And, specific to a windy site, a cap of the right design also stabilizes draft, because the hood breaks the downward push of a gust before it reaches the flue.

The sheet-metal lids on the newer houses

The subdivisions built out from the older core mostly have factory-built fireplaces in framed chases, topped with a sheet metal chase cover. Galvanized covers rust from the middle outward and then drip water down inside the chase where nobody can see it. By the time a stain appears on a ceiling below, the framing has been wet for a long time. A stainless replacement with a proper cross-break so water runs off rather than ponding is the permanent answer.

Top-sealing dampers

A throat damper is a metal flap and it never seals well. A top-sealing damper sits at the top of the flue with a silicone gasket and closes the chimney like a lid, which stops the heated air of your house going up it all summer and all night. In a house that also takes wind pressure at the chimney top, it stops the draft you feel in the room when the fireplace is not lit.

Waterproofing

Masonry is porous. A breathable siloxane repellent lets vapor out while keeping liquid water from soaking into the brick face, which is what makes freeze-thaw spalling possible. It is not paint and it is not a sealer, and putting an impermeable coating on a chimney traps moisture and makes the problem worse.