Green oak-framed
buildings are notoriously difficult to seal due to the movement that occurs
naturally as the oak dries and then from season to season.
However, thanks to a
variety of air- and vapour-tight barriers, sealants and gap-fillers from tremco illbruck, a
new-build oak-framed office building has achieved an astonishing airtightness
of 1.5m3/h/m2 rather than the expected 4.5-5.0m3/h/m2.
This is on a par with
a passive house, even though the office had not been designed as a low-energy
building.
The single-storey
office was constructed at the same time as a series of equine barns that were
being erected at a prestigious stud farm in Surrey.
The architect was very
familiar with designing oak-framed barns and stabling but was less familiar
with the building regulations relating to occupied buildings. Once the office
framework had been built, with brick infill at the lower levels and the roof covering
in place, the architect sought advice before the windows and doors were
installed.
By the time the expert
from tremco illbruck
became involved, the oak frame had been standing for almost six months and had,
to a large extent, stabilised – though it was fully expected to continue moving
for some time. The oak frame had numerous gaps and hollows between the
structural elements, and a complicated cavernous roof void. Fortunately the
range of illbruck products is extensive, so the optimum could be selected for
each area of application around the stud office.
Rob Halliwell, Area
Sales Manager (WF&S) for tremco illbruck Ltd, recommended a combination of
three products to provide an air- and vapour-tight barrier in the roof void and
extending down into the upper elevation of the ground floor. illbruck
ME003 Vapour Barrier is a three-ply co-extruded polyethylene (PE) membrane.
Although this is flexible and lightweight at only 110µm thick, it is
manufactured from high-grade polymer granulate so it is therefore both highly
vapour-retardant (sd >107m) and tear-resistant. To complement the vapour
barrier, Rob Halliwell proposed illbruck
ME317 Internal Membrane Tape, a single-sided, reinforced kraft paper tape
with solvent-free, modified acrylic adhesive for bonding the vapour barrier
overlaps. Easy to tear by hand, and with a release paper that can be removed as
the tape is applied long the joint, this product is very user-friendly. The
third product was
illbruck OT301 Endurance Adhesive, for bonding and forming an air-tight
seal between the ME003 vapour barrier and the structural elements. This
quick-drying, high-adhesion, high-elasticity adhesive suited this project well
because it was easy to apply and remains permanently flexible to cope with any
further movement in the oak frame.
One of the challenges
with the office project was to seal around the windows, which were installed
between stud partition infills that were hand-built in situ and were therefore vulnerable to unplanned air leakage
and vapour migration through the fabric layers. For sealing between the under
cill of the timber stud infill and the brick coping, Rob Halliwell recommended
illbruck FM330
Pro Foam Air Seal and illbruck
SP925 Air Seal. FM330 is a high-performance polyurethane (PU) foam that is
often used for filling and sealing construction joints, with its high movement
accommodation factor (35 per cent) ensuring that the seal is maintained even in
the event of movement. SP925 is a versatile multi-purpose product for
‘hard-to-seal’ areas that is applied the same way as other sealants - manually
or by spraying - and brushed out to ensure the area has been sealed fully.
Capable of filling gaps up to 6mm and 6mm deep with no backing material (or
wider, deeper gaps if a backing is applied first), SP925 dries to form a fully
elastic air- and weather-tight barrier that is excellent for areas that are
likely to be subject to movement.
For sealing between
the window perimeter and the studwork formed reveals, and also between the stud
partitions, the recommendation was to use illbruck
TP651 Trio impregnated pre-compressed sealing tape and ME500-W
Duo Flexible Window Membrane. T651 provides a weather-tight and air-tight
seal and, at the same time, thermal insulation such that the energy rating of
the window can be maintained for the installation. The soft open-cell PU foam
is pre-impregnated from one side using a flame-retardant synthetic resin, with
the one-sided impregnation resulting in different vapour diffusion properties
for the internal and external sides. Being pre-compressed, the tape is easy to
apply, yet it expands to fill and seal the gap extremely effectively, typically
taking a few hours to complete this process. The ME500-W intelligent membrane
achieves an air-tight and vapour-tight perimeter seal around the window frame,
with the membrane being applied around the frame prior to installation
(alternatively, ME500-E
can be applied post-installation). Manufactured from polyethylene copolymer
film, ME500-W also features a non-woven fleece fabric. Bonding to the window
frame is achieved with an acrylic self-adhesive strip, while bonding to the
wall is with a butyl self-adhesive strip. An integral movement pleat caters for
variable joint sizes and accommodates for any post-installation movement.
Elsewhere on project,
FM330 PU foam was used to provide thermal and acoustic insulation as required.
When tested for
airtightness, it was expected that the building would achieve in the order of
4.5-5.0m3/h/m2 but in fact the measurements showed a remarkable figure of 1.5m3/h/m2.
The experts commented that this was the best result they had ever assessed and
recorded; the figure of 1.5m3/h/m2 might typically be measured when
constructing a passive building, yet the architect had not set out with this as
a goal. Credit for this exceptional airtightness is due to the careful
selection of the optimum sealing and insulating products for the various areas
around the building, the ease with which they can be installed correctly, and
the technical performance of those products.
When Rob Halliwell
first visited the site he effectively had a ‘blank sheet of paper’ from which
to work, as the architect had not specified any sealing or gap-filling. He
therefore marked-up the architect’s drawings, supplemented by hand-drawn
sketches, to show his recommendations and make technical annotations.
Additional support was provided via telephone calls and email exchanges, and
the contractor watched the relevant ‘how to’ videos on illbruck’s
YouTube channel. Once all parties were satisfied that the recommended
illbruck products were right for the project, the order was placed with and
fulfilled by Grant Haze, one of tremco illbruck’s distribution partners.
Mike Williams of MWA Consultants, the firm of quantity
surveyors involved with the project, comments: “The airtightness of the
finished building was amazing and a real testament to the quality of the
materials. I was very impressed and, without a shadow of a doubt, I would
definitely use illbruck products again.”
