With growing demand for authentic slate roof products, Jeremy Lee, sales director for Aggregate Industries’
building products division, examines the age-old issue of grading and why cutting costs on materials might
not always deliver overall project cost savings
Construction of new homes in the
UK hit a 10 year high in 2017,
fuelling continued demand
for construction materials
including roof coverings. Amongst these
are natural slate, which is undergoing
something of a resurgence for its aesthetic
appeal and natural finish on a variety of
Whilst the newbuild sector accounts
for the majority of slate roof tiles, the
restoration market is booming too.
Air pollution in busy towns and cities
is reducing the lifecycle of slate roofs
originally designed to last 100 years
or more, and decades of condensation
from modern central heating systems
are beginning to take their toll too.
At Cambridge University’s King’s
College, for example, 15,500ft2 of roof
slates are being replaced this year
by restorers due to damage to the
underside of slates from condensation.
This demand for roof slates has
brought the issue of grading back into
focus – so often seen by contractors as
a costly, time-intensive and frustrating
process. And with a rising number
of lower quality imports coming into
the UK market to meet the growing
demand, it is becoming even more of a
hindrance for roofers on-site.
Exploring the issue
For many years, grading has been
seen as a necessary consequence of
using natural slate products to achieve
a better aesthetic finish. Roofers will
usually sort slate into at least three
separate grades to use on the eaves,
middle and ridges, which can be an
incredibly time-consuming process.
Whilst there will always be
differences with any natural product,
roofers have reported increases in the
time (and therefore cost) it takes to
grade roof slates in recent years, largely
due to the inferior quality of the natural
stone being brought into the market to
Lower grade slate often does
not offer consistency of thickness,
which not only makes grading a
lengthier process, but also affects
quantity surveying too. With such
inconsistencies, the number of tiles
on a pallet can vary from between 720
and 770 tiles with a lesser quality slate
So, is there a better solution? In short,
Grading in practice: Morse Roofing
Paul Morse from Morse Roofing in Lechlade, Gloucestershire, who has
been working with roof slates for more than 35 years, is one roofer to have
expressed concern at the increasing amount of time spent on grading.
He said: “Grading roof slates has always been something we’ve done to
improve the look and protect the integrity of a slate roof, but it’s obvious
to me that the quality of slate being sold in recent years means we’re
having to spend longer grading on-site.
“Any product that can reduce or even prevent the need for grading has
to be a good thing.
“It’s obvious that saving time on-site means we can move onto the next
job and ultimately keep costs down for the customer.
“Grading is becoming a major issue with some products. Clearly the
more we can control the consistency of slates, the better.”
yes; buy better quality slate, with better
consistency of thickness. It will cost
more of course – but with consistency
of thickness, there may be no need
for grading, which can deliver overall
project cost-savings when taking into
account the time saved on-site.
Bradstone’s Azul natural blue slate
roof tiles, for example, are made from
high quality slate originating from
north-west Spain. The product has
been specifically chosen not only for
its attractive, textured look, but for its
minimal grading requirements too.
Every single tile offers a nominal
thickness of 5-6mm, which guarantees
a minimum of 740 tiles on a pallet and
reduces the need to grade tiles.
It’s clear to see the potential to cut
the time on-site with such consistent
has been seen
as a necessary
thickness, especially when compared
with a lower quality, inconsistent
product, which would require
exhaustive manual grading.
Like any construction product, the
compromise over up front specification
cost and overall project cost is often a
difficult one to judge.
But with such variations between the
quality of natural slate being sold on
the market in recent years, even those
which achieve the necessary product
standard BS EN 12326, the clear and
demonstrable benefits of choosing a
consistent slate product have never been
80 www.rcimag.co.uk January 2019