EXTERNAL ENVELOPE 91
Designing airtightness into the build: What Modern Methods of Construction changes
M
odern Methods of Construction (MMC) has been gathering momentum across
Faster programmes,
some years now, and the reasons are well understood.
the UK for reduced
site labour, better quality control and more predictable outcomes. For architects, MMC also offers something that traditional on-site construction has always struggled to deliver consistently: the assurance that what was designed is actually what gets built. Airtightness is a good example of where this distinction matters. On a conventional build,
airtightness is heavily dependent on the standard of workmanship at any given moment on any given day. Weather, sequencing, subcontractor coordination and the sheer variability of manual installation all introduce risk. The designed air permeability target, unfortunately, doesn’t always match the fi gure recorded at the pressure test. Factory-based MMC changes this dynamic considerably. Controlled production environments mean consistent material supply, accurate cutting and fi xing, and quality checks at every stage. Whether computer-aided or robotically assisted, the process removes much of the human variability that causes airtightness failures on site. Panels and modules can be assembled to tight tolerances in conditions that no open building site can replicate, which means designed-in airtightness is far more likely to be achieved and verifi ed before anything leaves the factory. That said, MMC doesn’t eliminate the airtightness challenge entirely. It relocates it. The factory-built envelope may be excellent, but the interfaces between panels and modules — the connections made on site as the building is assembled — remain the critical weak points. Joints, corners, window and door openings, service penetrations: these are where the performance of an otherwise well-controlled build-up can unravel, and where specifi cation decisions made at the drawing board have the most direct impact on what the building actually delivers.
Where membrane specifi cation comes in For MMC projects, the membrane needs to do two things well. It needs to perform reliably in a factory environment — easy to apply, consistent in adhesion across the substrates
used in panelised or volumetric systems, and robust enough to survive handling, transport, weather and on-site assembly. And it needs to maintain airtightness at the junctions and openings that are made good once the building is in place. Proshield®
from Don & Low for walls
and fl oors addresses both. Its self-adhesive backing means it can be applied quickly and accurately in a factory setting without primers, tapes or mechanical fi xings, and it bonds directly to
the substrates most
commonly used in MMC construction: OSB, calcium silicate board, fi bre cement, gypsum board, steel, concrete and timber. A printed alignment grid is built into the membrane surface,
which helps
repeatable positioning. That’s particularly useful
when the same detail being
applied across hundreds of panels in a production run.
asset. It makes joints, overlaps and any gaps
visible
The bold blue colour is a practical immediately
during quality
inspection, both in the factory and during on-site assembly. In a process built around repeatability and quality control, that visual clarity has real value.
On airtightness performance, Proshield® has achieved KIWA certifi cation,
an
independent verifi cation that it performs as a truly airtight solution not just on uninterrupted panel surfaces, but at edges, corners and openings. This is the detail that
separates a membrane that works in theory from one that works in the real world. A full suite of matching tapes and preformed corners supports consistent,
repeatable
detailing at junctions, so the same standard of airtightness can be achieved across every connection in the assembly.
For projects targeting Passivhaus
certifi cation or designs infl uenced by Passivhaus principles, that level of verifi ed, repeatable performance at the details is what determines whether the standard is met or missed. Proshield®
contributes directly
to achieving the airtightness levels those standards demand. Class W1 water resistance, the highest
with consistent, is
classifi cation available, means the membrane performs across all geographical locations and exposure conditions in the UK. Plus,
Proshield’s Environmental Product Declaration gives specifi ers the documented environmental data increasingly required for responsible procurement and Scope 3 carbon reporting.
think
MMC is changing the way architects about construction
quality and
performance. Airtightness is one of the areas where that change is most tangible but only if the specifi cation supports it all the way through the assembly, not just across the easy stretches.
membranes@donlow.co.uk www.donlow.com
ADF APRIL/MAY 2026
WWW.ARCHITECTSDATAFILE.CO.UK
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