May 2021

Underlays
ROOFSHIELD EXPOSURE TESTS
The A. Proctor Group’s technical team carried out in-house exposure tests on
Roofshield in 2019 – purely for their own knowledge – which proved very timely and
provided some interesting findings for projects that were left exposed during
lockdown…
In early 2019, the A. Proctor Group’s (APG)
technical team began in-house testing to
measure the effects of extended outdoor
exposure on the performance properties of their
popular air and vapour permeable roofing
underlay, Roofshield.
Their timing was impeccable. Soon after the 12-
month test was complete, Covid-19 forced the
closure of some building sites across the UK while
at the same time the full effects of Brexit began to
be felt on supply chains, particularly that of roofing
battens and tiles. With this combination of
scenarios beyond anyone’s control, contractors had
no choice but to leave roofing membranes exposed
for longer than manufacturers’ recommendations.
The results of APG’s extended exposure testing
could not have arrived at a better time.
The maximum recommended exposure time for
any construction membrane is determined by
extensive testing by the manufacturer which looks
at the membrane’s basic components, any
additives, and the structure of the final product
itself. For some of the higher regarded
membranes, these recommendations are backed
up by independent third-party testing like LABC
and BBA. But, APG says, sometimes testing by
well-known industry figures in laboratory
conditions, however rigorous, isn’t the type of
reassurance people are looking for.
Never mind the chaos of a global pandemic or the
radical shakeup of a country’s well-worn economic
model. Everyday scenarios like delivery delays,
scheduling mix-ups, and even inclement weather
are what make ‘how long can a membrane be left
exposed for?’ one of the most common questions
that comes to APG’s technical department.
The original purpose of APG’s in-house tests then
Above: A. Proctor Group’s Roofshield underlay.
was not to re-write Roofshield’s 20+ years tried
and tested performance specification, rather, by
simulating a normal delay to a roofing project,
APG wanted to give contractors that extra bit of
reassurance.
It is important to understand here that, given the
purpose of the experiment, the ad hoc nature of
the test, and the small sample size, that the
findings of the 12-month trial described here are
anecdotal only. The results will not inform any
future changes to Roofshield’s current installation
guidance, performance specification, or
accreditations by third parties.
The test was carried out at the APG’s head office in
Blairgowrie, Scotland, between Jan 2019 and Jan
2020. The test consisted of sheets of Roofshield
being mechanically fixed to an angled wooden rig to
mimic a typical pitched roof installation. The
angled plane of the ‘roof’ was then oriented to be
south-facing to receive maximum UV exposure, and
care was taken to position the rig so that any risk
of shading was minimised.
Over the next 13 months, samples of the exposed
membrane were tested on a quarterly basis by
the independent testing organisation BTTG. A
sample of the membrane was tested at the
beginning of the trial to set a baseline against
which subsequent performance measurements
could be compared. The samples were tested
using the standard metrics for air and vapour
permeable roofing underlays: water penetration,
air permeability, and vapour permeability.
The results for air and vapour permeability were
excellent, with very little loss in performance.
While the samples’ performance with these
metrics did decrease gradually over time, the
results remained within Roofshield’s published
BBA-certified performance specification for the
entire 12-month experiment.
The 3, 6 and 9-month Roofshield samples all
achieved Class W1 for water penetration.
Considering the BBA Site Practice Bulletin Number
2 guidance is to protect any membrane that needs
to be left exposed for more than a few days with a
tarpaulin, APG regards this as outstanding.
This ensured that once the building sites were
open and the primary water shedding layer
installed, the roof underlay would perform its
main function of secondary water shedding,
vapour and air permeable. There was no need to
strip roofs and install new underlay.
The APG technical team wish to stress the results
of this or any other in-house test are not a licence
to ignore published guidance – and point out that
in the case of Roofshield, current recommendations
for handling, installation, storage, and maximum
exposure times should be followed. If a delay in
installing the primary covering – the slates, tiles –
on your roofing project is inevitable, APG says it is
always best practice to protect Roofshield with a
tarpaulin as soon as possible to keep UV exposure
to an absolute minimum.
Contact A Proctor Group
01250 872 261
www.proctorgroup.com
26 TC MAY 2021