Mast Architects Glasgow Case Study

Mast Architects Glasgow, Airtightness Project

Following a CPD presentation on
airtightness and how to achieve a
well designed and airtight
construction using Protect
membranes and sealing tapes,
Mast Architects of Glasgow called
on the expertise of the Protect
Membranes Technical department
to assist them in the preparation of
their design drawings for a range of
properties including houses and
flats across three separate sites in
Vineburg, Irvine.

The Proposal
The proposed developments followed
traditional timber kit design, consisting
of an outer brick skin 50mm cavity,
with an internal 140mm stud frame,
and using mineral wool insulation
minimum 20mm service void, finished
with a plasterboard lining. The brief
was to achieve air permeability less
than 6m3/h/m2.

The Solution
This was achieved by creating a
continuous airtight envelope within the
structure, linking the floor, wall and
roof/ceiling membranes to limit air

Protect VC Foil Ultra was specified to
line the inside face of all external walls.
This was combined with a 25mm service
cavity to help limit the number of
penetrations and potential air leakage
through the membranes, as a result of
services being fed around the building. If
space is at a premium, the minimum
20mm needed can be guaranteed by
using Protect Cavit-E clip which saves
the additional labour of adding an extra
25mm counterbatten.


All service penetrations passing through the Protect VC Foil Ultra were sealed with Protect Reveal tape. Overlaps in the membrane were sealed with Protect Reflective Sealing tape to maintain the additional thermal benefits to be gained from the Protect VC Foil Ultra. At door and window openings, the Protect VC Foil Ultra and Protect TF200 Thermo breather membranes used to clad the external face of the wall panels were cross sealed at the openings with Protect Reveal tape. This was to ensure there were no potential air leakage paths into the structure. Finally, all perimeter junctions of the walls were tape sealed with Protect Reveal tape.

The advantage of using Protect tapes was
such that all rooms could very quickly be
checked to ensure that the membranes
had been sealed. Unlike the use of double
sided tapes or mastic sealant, which have
to be physically checked to ensure
completion, the Protect range of tapes
with a high tack adhesive also ensures
compatibility with most building materials
without the need for additional site

One of the main difficulties in achieving an airtight envelope has been where the floor structure sits between the lower and upper floor panels. This is due to the necessity to ventilate the timber structure where exposed to the cavity, yet providing a continuous vapour control layer (VCL) across the wall. 

Protect Membranes developed a suitable airtight, yet breathable membrane, Protect FCM750 to overcome this difficulty. Lapped around the cavity end of the floor structure, the ends of the FCM750 are tape sealed to the inner VC Foil Ultra lining of the walls above and below using Protect Reveal tape.

Finally, at ceiling level, the trussed rafters were lined with Protect BarriAir, a highly effective air leakage barrier with vapour control properties. The membrane was tape sealed at all overlaps and perimeter junctions with Protect Reveal tape. Additionally, where ceiling battens were fitted to create a service void below the BarriAir, these were bedded on Protect Butyl Nail Sealing tape to limit air leakage through fixings. The air barrier across the ceiling was completed by the installation of a Glidevale loft access trap, which combined closed cell foam seals not only between the frame and lid, but also between frame and ceiling. The main benefit of a membrane and tape envelope airtight solution is that it allows a first fix pressure test before the final internal linings are fitted.

As a result of the airtightness design implemented using Protect airtightness solutions, testing across a range of properties including houses and 3 storey flats showed air leakage levels being achieved were as low as 2.2m3/h/m2 exceeding the design level required of lower than 6m3/h/m2.

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