How we size and fit a chimney cap: a Q&A with our crew

A chimney cap is one of the smallest and cheapest parts of a chimney, and one of the most important. Without it, rain goes straight down the flue, leaves pile up on the smoke shelf, and every bird and squirrel in the neighborhood has a warm place to nest. We asked our crew how they choose and fit a cap, from the first look up at the roof to the last screw.

How do you know a chimney needs a new cap?

• There is no cap at all. More common than people think on older Hill Country homes.
• The cap is rusted through, or the screen has rusted out or been pushed open by an animal.
• It is sitting crooked or loose after a storm.
• It is the wrong type for the chimney, for example a small single-flue cap on a chimney with two flues, leaving one open.

What do you measure?

Everything is measured from the roof, not guessed from the ground. For a cap that sits on one flue tile, we measure the outside of the tile, length and width, and how high it sticks up above the crown. For a cap that covers the whole top, we measure the crown itself and every flue on it. A cap that is a little too big rattles and moves in wind. A little too small does not go on at all.

Single-flue or the whole top?

If there is one flue tile and a sound crown, a single-flue cap is the simple answer. If there are two or more flues, or the crown is in rough shape, an outside-mount cap that covers the whole top protects more of the chimney from water. On the brick chimney in the photo with this article, the old screen cap had rusted and the crown under it had worn down, so both were replaced: a new crown first, then a new metal cover over the flue.

Does the mesh matter?

Yes. The screen keeps animals and debris out and catches embers. Too fine and it clogs with soot on a wood-burning fireplace and starts choking the draft. Too coarse and it does not stop much. We pick the mesh for how you use the fireplace, and we look at the screen every time we sweep.

What metal do you use?

Galvanized steel is cheap and rusts. Stainless steel is what we recommend for most homes because it lasts. Copper and powder-coated black caps cost more and are chosen for looks on visible chimneys. Whatever the metal, the fasteners have to match it, or the screws rust out first.

What has to be right before the cap goes on?

The crown. A cap on top of a cracked crown still lets water into the masonry around the flue. So before we fit a cap, we photograph the crown, the mortar joints near the top and the flashing where the chimney meets the roof. If the crown needs repair, we price it separately and do it first, and the cap goes on a sound top.

Get it looked at

The inspection is free and covers the roof: cap, crown and flashing, all photographed. Through October 31, 2026 we take 10% off chimney brick and stone repair booked after an inspection. We work across Marble Falls, Horseshoe Bay, Burnet, Georgetown, Leander and the Hill Country.