Chimney repair in Lakewood.

1. Crowns.

   At the top of the masonry sits the crown, a slab of concrete. Rain and snowmelt cross it on their way off the roof, clear of the brick and flue, so it takes more weather than any other part.

   NOAA's normals for the Lakewood station put a January day between 21.1°F and 44.8°F, and the overnight low at or under freezing on 153.8 days a year. On each such night, ice in a hairline crack pushes it open slightly more. Hairline cracks can be sealed. If the slab is crumbling or has separated from the liner, it must be removed and recast.

   

2. Caps and mesh.

   Birds, squirrels, rain and snow are kept out by the cap, and its screen is also what stops sparks. The International Residential Code, section R1003.9.2, sets 1/2 inch as the widest permitted opening.

   Metal caps get dented by hail, shaken loose by wind and eaten by rust. After a storm, look for dents, screws that have backed out, rusty seams and a screen that sags or is clogged.

   

3. Flashing around the base.

   Flashing closes the joint where the chimney meets the roof. Wet snow drains off slowly on the uphill side, so a lifted edge or a worn bead of sealant usually leaks along that line. Indoors, the first clue is often a brown stain on the ceiling, or a damp attic wall next to the chimney.

   

4. Brick and the joints between it.

   Mortar is meant to give way before brick does. Once the joints open, moisture creeps behind the brick face, and each freeze can lift off a flake, which is called spalling.

   Tuckpointing rakes out the weathered mortar and packs in new before bricks start to shift. A brick that has cracked right through or flaked deeply is cut out and replaced.

5. Inside the firebox.

   Fire and heat press directly on the firebrick and the mortar between. When joints gape and bricks split, heat can travel to the framing behind, so a small gap closed early protects the woodwork.

   

6. The liner and its tiles.

   From damper to cap, the liner carries smoke and heat away from the house. A cracked or shifted tile, or a metal seam that has rusted through, can let heat reach framing and fumes reach rooms, and from the roof or the firebox the fault often cannot be seen. A camera passed up the flue reveals it, as does a Level 2 inspection. Lakewood's median house was built in 1977, which puts a typical flue near fifty years of service.

   

7. Metal covers on framed chimneys.

   Not every chimney is masonry. Some are a wood-framed box finished to match the house, topped with a sheet-metal cover. When that cover corrodes through or sags, water pools on it and runs down into the chase. A screened cap on the flue, set under a cover that sheds water, keeps the interior dry.

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