September 2020

Perfectly Pitched
CONSULTANT CASE STUDY: A
FOCUS ON THE CLAY PANTILES
In his latest column, pitched roofing consultant John Mercer turns his attention to the
installation of traditional clay pantiles, and references two recent roof inspections he was
called out to where things had gone wrong…
In this, my third article in a series of case
studies of actual site investigations, I turn my
attention to traditional clay pantiles. I am
using examples from two recent roof inspections,
each involving clay pantiles, though from different
manufacturers.
Clay pantiles have been a familiar
sight in the UK roofscape for
hundreds of years, dating back at
least as far as the 16th century,
though pantiles base their
appearance on the ‘over and
under’ tiles introduced by the
Romans.
Traditional pantile design has not
changed much in all that time,
Above: Diagram shows the relationship between linear and
gauge adjustment.
though, of course, manufacturing
techniques have improved
hugely, enabling far greater
precision in the drying and
firing stages, as well as the
dimensional accuracy of the
finished products.
Traditional clay pantiles are
generally considered to be ‘fixed gauge’,
which means the contractor must determine
the most appropriate gauge for the batch of tiles
arriving on site. However, there is a relationship
between gauge and linear coverage such that
adjustment to gauge has an impact on linear
coverage, and vice versa. This means that, in
experienced hands, pantiles can be very versatile
in the way they are installed. But, in
inexperienced hands, that very versatility can
John Mercer, Pitched Roofing Consultant.
lead to all sorts of problems, as
I will demonstrate below.
Setting out
In this photo (below), the tile
gauge and the linear coverage
have been ‘stretched’ leading to large
gaps between the tiles at the mitre corners.
Apart from the untidy appearance of the tiling,
stretching the batten gauge reduces the effective
headlap between tile courses, so the combined
problems of large gaps and reduced headlap
increases the risk of driven rain ingress. To some
extent, the large gaps could be lessened by
decreasing the linear coverage, in other words by
Continued on page 26
Above: the tile gauge and the linear coverage have been ‘stretched’ leading to large gaps between the tiles at the mitre corners.
24 TC SEPTEMBER 2020