Building better, off-site: what we've learned from Modern Methods of Construction
Modern Methods of Construction (MMC) gets talked about a great deal, and often in the abstract. At ReFrame Studio, we've taken a more hands-on view: across our projects, we've designed and delivered with four different off-site systems - WikiHouse, SIPs, insulated Concrete Formwork (ICF) and Closed-Panel Timber. Each has its own character, and each has taught us something about where off-site really earns its place.
This post looks at those four systems through the projects we've built with them, and offers an honest account of why we so often start by looking off-site.
Why we look off-site first
Traditional, brick-by-brick construction is familiar and flexible, but it puts a lot of the build in the hands of the weather, the availability of skilled trades, and decisions made late on a muddy site. Off-site methods move much of that work into a controlled factory environment, and that shift changes the project in some genuinely useful ways:
Cost certainty, earlier. A large share of the build cost is fixed when the kit or panels are ordered, rather than emerging week by week on site. That gives our clients a much clearer financial picture at the point it matters most, before the ground is broken.
Precision manufacture, and a better building for it. Components are cut and assembled to fine tolerances in the factory, so things fit as designed. That precision translates directly into performance: excellent airtightness, minimal thermal bridging and low U-values, which means a warmer, quieter, cheaper-to-run home.
Less waste. Cutting to size in a controlled setting produces far less offcut and spoil than a conventional site, and what is left over is easier to recycle. It's better for the budget and better for the planet.
Speed, and weathertight sooner. A structure that arrives largely pre-made goes up quickly. Getting a building watertight in days rather than weeks protects the works and lets the following trades start earlier.
Fewer surprises. Factory quality control catches issues before they reach the site, and a tidier, faster, safer site means less disruption, which matters especially on extensions, where people are often still living next to the works.
None of this makes off-site the right answer every time. But it does mean it deserves a serious look at the outset of nearly every project we take on.
The systems we've built with
WikiHouse: The Bothy, at The Bide
The Bothy, the first of our two eco-cabins at The Bide in Dorset, was built using WikiHouse: an open-source system of plywood components, digitally designed and CNC-cut, that slot together on site with very little heavy plant or specialist labour. It's about as clear an expression of digital manufacturing as you'll find in housebuilding . The design file and the building are, in effect, the same thing. We built The Bothy ourselves during lockdown, which gave us a hands-on understanding of the system that now feeds straight back into our clients' projects, and you can even book a stay in it.
For a low-impact cabin in a sensitive rural setting, it was an ideal fit. The frame went up fast and quietly, the embodied carbon is low thanks to the timber-based structure, and the precision of the cut components made for a tight, well-performing envelope. It's a system we believe in enough to offer as a route for our own clients, and you can read more about our WikiHouse work and see the project in detail.
SIPs: The Nest, and our extension at Silverlakes
Structural insulated panels (SIPs) sandwich a rigid insulation core between two structural boards, producing a panel that is strong, highly insulated and remarkably airtight all in one. We used SIPs for The Nest, the second cabin at The Bide, and for a residential extension at Silverlakes. The appeal is easy to see in both: the panels arrive cut to the design, the shell goes up quickly, and the thermal performance you get almost as a by-product is very hard to match with traditional construction.
Where a client wants a high-performing, airtight envelope without the on-site labour and weather exposure of a conventional build, SIPs are consistently one of our first suggestions. They particularly suit projects with vaulted ceilings, as they're one of the few systems able to form the roof as well as the walls, avoiding the need for conventional timber joist work on site.
ICF: Southern Wood
Insulated concrete formwork (ICF) takes a different route to the same goal. Hollow, interlocking insulation forms are stacked on site and filled with reinforced concrete, leaving you with a structure that is insulated inside and out and remarkably robust. We used ICF at Southern Wood, a woodland barn-style new build where the combination of thermal mass and continuous insulation was well suited to the brief.
It's worth being clear that ICF sits slightly differently to the panelised systems. The forms are manufactured off-site, but the concrete is poured on site, so it's something of a hybrid. What you gain is a building that is exceptionally strong, airtight, quiet and thermally stable, holding an even temperature through the seasons. For clients who value solidity and long-term performance, it's a compelling option.
Closed-panel timber: Sandhills Cottage
At Sandhills Cottage, we specified off-site closed-panel timber frame. Where an open-panel system arrives as a bare frame, closed panels come from the factory far more complete. Insulation, membranes and often services are already built in, so the structure reaches weathertight remarkably quickly once it's on site.
This is off-site manufacture at its most developed: the factory does the detailed, quality-critical work in controlled conditions, and the site work becomes a matter of assembly largely. The result is a high-performing, low-waste build with a predictable programme, precisely the qualities that make MMC worth the effort.
Choosing the right system
MMC isn't a single thing. In the UK it spans seven recognised categories, from fully volumetric modular buildings through to improvements in on-site process and, as our four projects show, the right choice depends entirely on the site, the brief, the budget and the client's priorities.
That's the part we most enjoy. Having designed and delivered across WikiHouse, SIPs, ICF and closed-panel timber, we're able to weigh these systems against a project on their merits, rather than defaulting to whatever is most familiar. The common thread is that, used well, all of them deliver a better building: more certain on cost, more precise in the making, and higher performing in use.
A couple of questions we're often asked
Does MMC mean my project isn't fully bespoke?
Not at all, and it's the misconception we hear most. People often picture MMC as identical modular boxes rolling off a production line, but that's only one corner of it (volumetric modular), and it isn't how we work.
The systems we use (WikiHouse, SIPs, ICF) and closed-panel timber are made to your design, not the other way round. We draw the building first, and the components are then cut and manufactured to those drawings.
With the digitally fabricated systems especially, your design is effectively the instruction sent to the factory, so there's no loss of individuality; if anything, the precision lets us hold fine detail more faithfully than a hand-built site can. Every project mentioned here is a genuine one-off.
Will MMC cost me more money?
The honest answer is: usually not, but it depends what you're comparing. The panel or kit package isn't always the cheapest single line in a budget, and it's fair to expect the headline build cost to land close to a good traditional build rather than dramatically below it.
Where MMC pays off is across the whole picture: far greater cost certainty early on, a shorter programme (which trims site preliminaries and finance, and for extensions the disruption of living through the works), less wasted material, and a high-performing building that costs markedly less to run over its lifetime.
So while it isn't a guaranteed saving on day one, it very often works out better value once time, risk and running costs are taken into account. We'll always be straight with you about where a given system sits on cost for your particular project.
Talk to us
If you're planning a new home, an extension or a replacement dwelling and want to understand which approach would serve you best, we'd be glad to talk it through. You can browse more of our projects or get in touch for a free initial consultation.
ReFrame Studio is a RIBA Chartered Practice with studios in Bournemouth and Bath, working on new builds, extensions and refurbishments across Dorset, the South East and beyond.