A chimney chase is the framed enclosure, often covered in siding or veneer, that surrounds a factory-built metal chimney or flue running up the outside of a house. Once water gets past the chase cover or flashing, it soaks into the framing and insulation inside the chase, rusts metal fasteners and the flue pipe itself, and can eventually reach the wood structure of the house, causing rot that's expensive to find and fix because most of it is hidden behind the siding.
Chase covers sit on top of the chase like a small roof, usually metal, and they're a common weak point. A chase cover that's rusted through, poorly sealed at the seams, or was never properly flashed against the house lets rain track straight down into the enclosure below. Because the inside of a chase is framed with wood and often has minimal drainage built in, water that gets in doesn't have an easy way back out on its own.
In a climate with regular freeze-thaw cycles, water sitting inside a chase does more damage than a single soaking would suggest. It freezes, expands against whatever it's touching inside the chase, thaws, and repeats through the winter. Insulation loses its effectiveness once it's wet, fasteners rust and lose their grip, and framing that stays damp through multiple freeze cycles starts to rot rather than just getting wet and drying back out.
A masonry chimney doesn't have a chase in the same sense, but the same principle applies to the crown and flashing where the chimney meets the roof. We check chase covers and roof flashing as part of chimney work because water intrusion at those points causes damage that's largely invisible until it's serious, whether it's a wood-framed chase or the flashing seam around a masonry chimney.
More on this from Chelo's Brick & Stone.
Chelo's Brick & Stone serves Hillsville, Galax, Wytheville, Fancy Gap, and Independence, VA. Call for a straight answer and a free on-site estimate.
