Drip edge is metal edging that is installed
on the bottom edge of the eaves (called the “drip edge”)
where water drips off the roof. The product was primarily
invented and widely manufactured to accompany asphalt
shingle installations. This is because asphalt shingles
have little structural integrity and will sag over the
edge of a roof if allowed to extend beyond the roof edge.
Of course, the shingles must extend beyond the roof edge
in order to allow the water to drip off the roof rather
than run down the side of the building. Since asphalt
shingles cannot extend beyond the edge of a roof without
support, metal “drip
edge” was invented to
provide that support — to hold the shingles up
so they don’t sag.
Slate shingles, being stone, have a lot
of structural integrity and will not sag over the edge
of a roof. They, therefore, do not require a separate
metal drip edge for support and such edgings have never
been traditionally used on slate roofs, except in certain
situations. These situations may include, for example,
when a slate roof ties into some types of metal roofs,
or perhaps when it ties into some types of built-in
metal gutters. Metal edgings have also been used on
slate roofs for stylistic reasons — for decoration.
In general, however, metal drip edges are not needed
on slate roofs.
Then Why Use a Metal Drip Edge?
For three basic reasons:
1) Today, many slate roofs are installed by roofers
whose primary work has been with asphalt shingles. They
often use decking materials that would be considered
sub-standard when compared to traditional wood board
slate roof decks.Such sub-standard decking materials
include plywoods, particle boards, OSB, and anything
that is held together with glue. These decking materials
are not as durable as wood boards and can benefit by
having their exposed edges protected by a metal edging,
both at the drip edge and along
the sides of the roof (also known as the gable or rake edges). Therefore, metal drip
edges have become popular for slate roofs among many
asphalt shingle roofing contractors.
2) In addition, some contractors and building owners
like the look of a copper edging on a roof system. It
adds a rich appearance that compliments the slate and
the copper flashings. The small additional cost of copper
roof edgings can add a measure of protection as well
as additional quality to a slate roof installation.
3) When copper roof edgings are used
on a slate roof installation, the standard wooden cant
strip that is required at the starter course along
the eaves can be competely eliminated and replaced
with a copper roof edging that has the cant
built right into it. This creates a permanent copper cant strip
that is quickly and easily installed. Many inexperienced
roofers forget to install the cant strip in the first
place. By using a copper edge with a built-in cant,
they can’t go wrong
(no pun intended).
Are Slate Roof Drip Edges Different From Asphalt
Shingle Drip Edge?
YES! Standard asphalt shingle drip edges
are designed to prop up the shingles so they don’t sag over
the edge of the roof. Slate don’t sag, but they
also don’t lie flat on the roof surface. Every
slate is lying at an angle on the roof. This means that
any part of a metal edging that extends beyond the roof
edge will be serving no purpose on a slate roof because
such extensions will not even come in contact with the
slate. The slate shingles create their own “drip
edge” so the metal edging’s primary purpose
is to protect the roof edge, not support the shingles.
Therefore, a slate roof “drip edge” will
not have the horizontal lip that is needed on asphalt
shingle drip edges. This does not mean that asphalt shingle
drip edges with the horizontal lip cannot be used on
slate roofs — they can. But a metal edging made
specifically for slate roofs will not necessarily have
the horizontal lip, which serves no practical purpose.