Chimney Flashing
Stop Roof Leaks
Introduction: One of the critical steps in building a chimney
is to properly install the flashing where the chimney passes through
the roof to prevent water leakage.
By building code, the chimney
must be at least two inches from any wood structure which means
there is a two inch gap between the chimney and the roof. That is
where the chimney flashing comes into play. It is stalled around the
chimney
to
prevent water from entering the gap and running down the chimney
inside the house. On a conventional masonry chimney or brick
chimney, lead flashing is used because it is pliable and will not
deteriorate. The flashing is inserted between the bricks and then
folded down to meet the roof line. In recent years the lead flashing
has been replaced by tin, copper and
aluminum.
Metal
chimneys such as stainless steel chimneys use a metal boot
arrangement to close the opening between the chimney and the wood
structure. It is usually made of aluminum or galvanized sheet metal.
The boot slips over the chimney pipe and is attached to the roof.
If
you have water spots on your ceiling near the chimney area or water
running down the side of the chimney into the basement the cause is
most likely from a chimney flashing leak. Chimney flashing leaks are
quite common due to the fact that chimneys are not directly attached
to the house structure. All houses settle in the first few years
after construction which causes the chimney flashing to pull away
from the chimney causing flashing leaks.
There are other reasons for flashing to fail.
Flashing made from tin, copper, aluminum and galvanized sheet metal
corrodes due to the weather and the continuous expansion and
contraction of the metal. Eventually the flashing begins to leak.
Lead flashing is nearly impervious to corrosion and will last for
decades without leaking.
If the flashing is either cemented into the chimney mortar or
is sealed to the chimney and the roof by a polyurethane caulk. Over
time the caulk dries out and crack allowing water to penetrate
underneath the chimney flashing and eventually show up on your
ceilings.
When roof shingles are replaced the chimney
flashing should be inspected for deterioration. Any deteriorated
flashing should be replaced at this time. If it is in good condition
replace the sealing caulk. If you are a DIY handyman and do your own
roofing repairs you should keep in mind that working on roofs can be
a dangerous job. You should wear proper rubber-soled shoes and
clothing. Wear a harness that is attached to the roof to prevent
falling from the roof. Walk as little as possible on the roofing
shingles. Excessive foot traffic can damage the shingles.
See more DIY construction projects.
