Modern Methods of Construction (MMC) has been gathering momentum across the UK for some years now, and the reasons are well understood. Faster programmes, 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 figure recorded at the pressure test.
Factory-based MMC changes this dynamic considerably. Controlled production environments mean consistent material supply, accurate cutting and fixing, 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 verified 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 specification decisions made at the drawing board have the most direct impact on what the building actually delivers.
Where membrane specification 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 floors addresses both. Its self-adhesive backing means it can be applied quickly and accurately in a factory setting without primers, tapes or mechanical fixings, and it bonds directly to the substrates most commonly used in MMC construction: OSB, calcium silicate board, fibre cement, gypsum board, steel, concrete and timber. A printed alignment grid is built into the membrane surface, which helps with consistent, repeatable positioning. That’s particularly useful when the same detail is being applied across hundreds of panels in a production run.
The bold blue colour is a practical asset. It makes joints, overlaps and any gaps immediately visible 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 certification, an independent verification 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 certification or designs influenced by Passivhaus principles, that level of verified, 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 classification available, means the membrane performs across all geographical locations and exposure conditions in the UK. Plus, Proshield’s Environmental Product Declaration gives specifiers the documented environmental data increasingly required for responsible procurement and Scope 3 carbon reporting.
MMC is changing the way architects think about construction quality and performance. Airtightness is one of the areas where that change is most tangible but only if the specification supports it all the way through the assembly, not just across the easy stretches.