Caps, Screens and Tree Cover in Pleasant Grove

What the canopy does to a chimney

On the older blocks in Pleasant Grove that canopy now stands well above the rooflines, which puts leaf litter and squirrels directly over the flue rather than off to one side of it. Chimneys built to clear a young tree are not clearing that.

Three separate problems come from having large trees close to a house, and they are worth separating because they have different answers.

The first is debris. Leaves, twigs and seed cases land on a crown or a chase top and stay there, and an uncapped flue collects them directly. That material holds water against the masonry, and in a flue it is a blockage and a fire load in the worst possible position. A cap with a stainless mesh screen ends it, and it also keeps out the birds that a mature canopy naturally attracts, which are otherwise a reliable spring problem.

The second is shade. Masonry under a tree gets less sun and less wind, so it dries more slowly after every storm and every melt. A crown that stays damp going into a freeze is a crown that is being taken apart from the inside. This is why waterproofing is more valuable on a shaded chimney than a sunny one, and why moss or dark staining on the north side of a crown is a sign worth acting on rather than washing off.

The third is draft, and it is the one nobody expects. A chimney has to terminate high enough above nearby obstructions to sit in clean air. Trees that were modest when the house was built are not modest twenty-five years later, and a chimney that once cleared everything around it can end up sitting in the wind shadow of a mature canopy. The symptom is a fireplace that drafts inconsistently and gets noticeably worse on breezy days. Sometimes the fix is extending the flue. Sometimes it is a wind-directional cap. Occasionally it is trimming a limb.

Getting the details right

Stainless rather than galvanized, because galvanized rusts in this climate and streaks the masonry below it while it does. A screen with enough open area that it does not restrict the flue, and a lid with a real overhang so water is thrown clear of the crown rather than running down the brick. For masonry that has already been kept damp for years, a breathable siloxane repellent applied to sound brick sheds liquid water while still letting vapor out. Never a film-forming sealer, which traps moisture in the brick and hands the next freeze exactly what it needs.