What Is Apron Flashing?
Apron flashing (head flashing) protects the low side of a chimney, dormer face, or headwall — anywhere shingles run up and stop against a vertical face. It is one continuous L-shaped piece: the vertical leg rises several inches up the wall behind siding or counter-flashing, and the horizontal leg extends over the top of the shingle course below, so water washing down the wall is delivered onto the roof surface rather than behind it. It fails when the horizontal leg is too short and water blows back under it, when it is nailed through the exposed face and the nail seals fail, or when it is buried under a shingle instead of over one, reversing the lap. Homeowners see stains at the ceiling directly below a chimney's downhill face. Replacement involves removing the counter-flashing or siding above it and at least one shingle course below, then installing a new apron with correct overlap and concealed fastening.
Important Distinction
Note: Apron flashing sits on the DOWNHILL side of an obstruction and sheds water onto shingles; the uphill side needs a back pan or cricket, and confusing the two leaves the high side unprotected.
Also Known As
These are the search terms and phrases that commonly refer to this topic, so you can find it however you describe it.
How Apron Flashing Relates to Other Topics
Apron flashing at the downhill face of a chimney or dormer laps OVER the shingles below it, while flashing above laps under - reverse the lap and the roof is built to leak on day one.
Related To Apron Flashing
Flashing handles the sides and downhill face of a chimney, but the uphill side collects water and debris; that is the cricket's job - a small peaked diverter that splits the flow around the masonry.
Questions about Apron Flashing?
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