Slate Roofing's "Dirty Secret"

Slate Roofing’s “Dirty Secret”
Slate roofing is composed of slabs of rock mined
from a quarry, cut and then split. Two holes are
then made at the top of each slate for the
fasteners. Slate is available in a variety of natural
colors and also in different grades that affect their
projected roof life.
Slate can be use on roofs that have a slope of 4:12
and over, providing the roof is strong enough to
support the heavy weight. That usually requires an
engineering inspection, if the home wasn’t
originally designed for a slate roof.
Benefits of slate roofing. Slate has a distinctive
look that is very attractive, especially when it is
fairly new and all the slates are in good shape.
Slates are basically slabs of rock. As such, they
tend to last a very long time. There are slate roofs
that over 100 years old.
They also won’t burn, giving them a Class A fire
rating.
Problems with slate roofing. Slate roofs are the
most expensive roof system you can buy, with the
material alone costing more than the entire
reroofing cost for most other systems.
The price is justified by the argument that slate is a
“permanent” roof that will last for 100-plus years.
Indeed, the rock may last for a century or more,
BUT THE REST OF THE ROOF SYSTEM WILL
NOT!
Flashings and underlayment will deteriorate long
before then. Broken slates and installation errors
result in leaks, just like they do with every other
type of roofing.
When that happens on most systems, the old
roofing is removed and disposed of. Repairs to the
roof deck are made and new roofing is installed.
It’s a relatively fast and cost-effective process that
most roofing companies have down to a science.
But when slate roofs fail, the slate is so expensive,
it is often carefully removed and set aside for
reinstallation after the rest of the work is done.
Slate can become brittle as it ages and some is
damaged in the removal process.
So new slate must be found to match the natural
colors found in the quarry where it was first
mined… DECADES PREVIOUSLY. And don’t
forget the expense of shipping rock around the
country.
Salvaging the old slate is labor-intensive work and
much of the savings in material is lost in the labor
to do so. Installing slate is also labor intensive and
is somewhat of an art. It’s not a good do-it-yourself
project.
My opinion of slate roofing: While slate roofs
are very attractive, this blog is about saving you
thousands of dollars.
The “dirty little secret” with slate roofs is that while
the rock may last for a century or more, the rest of
the roof system will not.
With the high initial cost, high reroofing cost and a
roof life much less than advertised, the life-cycle
cost of slate is enormous.
You can do better… for a lot less money.
If you choose slate anyway… Say you have a
historical building where you don’t have any choice
or you have more money than you know what to
do with…
Be sure to use a roofing contractor who
specializes in slate. You want a guy who does it all
the time and knows the finer points. Most roofers
don’t have a clue about slate, because they
seldom run into it. I’ve been roofing 22 years and
have only worked on a few slate roofs.
Be open to flashing upgrades and premium
underlayments. That will help to extend the roof life
and lower your overall roof cycle costs. If you’re
going with slate, this is no place to cut corners.
www.macgregorroofing.com