Apron Flashing
A continuous piece of sheet metal installed at the base of a vertical surface where it meets the roof plane, such as at the front of a chimney or dormer. Directs water flowing down the vertical surface onto the shingles.
What Is Apron Flashing
Apron flashing is a continuous, L-shaped piece of metal installed horizontally at the base of a vertical surface where it intersects the roof plane, directing water that runs down the wall onto the shingle surface below. Unlike step flashing, which is installed in individual overlapping pieces along the side of a wall, apron flashing spans the full width of the obstruction in a single piece. It is most commonly found on the uphill side of chimneys and at the base of dormers.
How Apron Flashing Works
The vertical leg of the apron flashing extends up the wall or chimney face, while the horizontal leg lays flat on the roof deck beneath the shingles. Water running down the chimney or wall hits the vertical leg and is redirected onto the roof surface. On masonry chimneys, the top edge of the apron is typically embedded in a reglet (a groove cut into the mortar joint) and sealed with urethane caulk.
Apron Flashing in Insurance Estimates
In Xactimate, apron flashing is measured in linear feet and carries its own line item separate from step flashing and counter flashing. When a chimney or dormer is involved in a claim, inspect the apron flashing for rust, lifted edges, cracked sealant, or displacement from wind or impact. If the apron flashing needs replacement, the shingles surrounding it must also be removed and reinstalled, which adds labor and material line items to the estimate.
Frequently asked questions
Apron flashing is a single piece of bent metal installed where a vertical surface like a chimney or dormer face meets the roof deck on the uphill side. It spans the full width of the obstruction and tucks under the siding or into a reglet cut in the masonry above.
Apron flashing is most commonly found at the front (uphill side) of chimneys, at the base of dormers, and where additions or second-story walls meet a lower roof. Any location where water running down a vertical surface needs to be deflected onto the roof plane uses apron flashing.
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