The short answer
Roofs often leak around chimneys, skylights and vents because those spots depend on flashing, thin metal or rubber pieces that seal the joint. Flashing can rust, shift or pull loose, sealant dries out, and pipe boots crack with age. Fixing the flashing usually fixes the leak.
On this page
What flashing is
Flashing is thin metal, often aluminum or galvanized steel, that is shaped to guide water over a joint where the roof meets something else. It is used at chimneys, skylights, walls, valleys and vent pipes.
Shingles shed water well on open roof areas, but a joint is a weak point. Flashing carries water over that joint and back onto the shingles.
Chimneys and skylights
Chimneys use layers of flashing. Step flashing is bent metal pieces woven in with each shingle course along the side of the chimney. Counter flashing is set into the brick or mortar and laps over the step flashing. If the mortar crumbles or the metal pulls away, water gets in.
Skylights have flashing kits, or a raised curb, around the frame. Leaks there can come from worn flashing or a cracked seal. Because water can travel along framing, a stain may show up far from the real source.
Vent pipes and caulk
Plumbing vents and other pipes pass through the roof with a rubber or plastic boot, also called a collar. Sun and cold crack that rubber with age, and the gap lets water run down the pipe into the house.
Caulk or roofing sealant can slow a small leak for a while, but it dries and cracks. Treat it as a temporary patch. A lasting fix usually means replacing the boot or flashing.
Clues inside the house
Look for brown or yellow ceiling stains near a chimney wall, skylight or bathroom vent. Peeling paint, a musty smell, damp insulation in the attic and drips during snowmelt all point to a flashing leak.
Note when the leak happens. Leaks only in heavy rain, or only as snow melts, give a roofing pro useful clues. Take photos, and see the related article below on how to find a leak.
Want a local pro to take a look? Request a quote and add a photo. Quotes provided by our network of licensed, insured local contractors to get you top quality at a fair price.
Related service: Roof repair in Rochester, MN. Browse the towns we cover or all roofing guides.