Rollalong Offsite Construction Ltd work with a variety of clients, including housing associations and the Ministry of Defence, whose requirements are changing to address the climate emergency.
Darren Evans provided a variety of services supporting Rollalong Offsite Construction’s tender submissions to meet new technical requirements for fabric first and net zero construction.
For the construction industry to reduce its carbon emissions and contribute to net zero targets, it must adapt and produce buildings in a different way. Prefabrication is not new but embracing offsite manufacture as a ‘modern method of construction’ offers one potential route to reducing the whole life carbon of buildings – that is, both their operational emissions and their embodied carbon emissions.
Offsite manufacture offers several challenges compared to traditional construction. Because it removes a lot of on-site processes, the emissions associated with a project change. Carbon is still emitted, however, so the question is how best to account for the emissions associated with the prefabrication part of the process.
Modular construction is also used to provide buildings for specialist areas of construction. These buildings must still comply with regulations and demonstrate low energy performance, but the measurement of that performance compared to ‘standard’ residential or commercial uses must be done with care to ensure it is accurate.
An area that Rollalong Offsite Construction specialise in is defence buildings. The Ministry of Defence (MOD) sets clear technical requirements for any project they put out to tender. A result of the UK government’s legally binding net zero target, there has been a significant shift in those requirements.
“In recent years we’ve produced 55 buildings for the MOD, used across Salisbury Plain,” explains Roger Sitch, Head of Design and Technical Compliance at Rollalong Offsite Construction. “All of them met the requirements of Part L 2013. Our most recent tender submission, however, had to meet fabric first and net zero benchmarks, which was quite a dramatic change.”
As a result, the proposed solution was also a dramatic change – but not just for energy and carbon reasons. Other industry trends played a part, as Roger describes: “The returned tender was more expensive compared to the previous projects. As well as meeting the tighter energy benchmarks, the walls featured non-combustible insulation, which meant an overall increase in wall thickness.”
Defence buildings must be bomb resistant, featuring additional steel sheets to protect occupants from shrapnel. That adds extra material and extra embodied carbon, which the submission had to account for while still meeting the additional performance needs of the building. Collaboration was key to making the best quality tender submission.
“Darren Evans supported us with the evidence we submitted,” says Roger. “We also worked closely with an M&E subcontractor. The client is looking for the best cost, and together we came up with the most effective solution to achieve the targets without compromising quality.”
Buildings for the defence sector still must comply with national building regulations. However, in demonstrating compliance as part of the tender submission, the accepted route to doing so was not available for a building designed to serve as a barracks.
The national calculation methodology (NCM) that is used for regulatory compliance relies on user profiles. Each profile makes certain assumptions based on the building type and predicted occupancy, and those assumptions are used in simplified building energy model (SBEM) calculations.
“From an energy profile point of view, the latest tender submission was not a normal occupied space,” says Brandon Wipperfurth, Senior Sustainability and Energy Consultant at Darren Evans.
“It’s not family accommodation, and it doesn’t have a consistent occupancy pattern. The closest appropriate profile for a barracks was university accommodation, but it still wasn’t accurate enough. We explored the intermittent occupation as part of our analysis, adapting the university accommodation profile in a dynamic simulation model (DSM) as a route to compliance instead.”
Determining regulatory compliance was just one of two assessments carried out for the tender submission, as it was also necessary to show how the enhanced fabric first and net zero technical requirements would be met.
Darren Evans therefore prepared embodied carbon and operational energy analysis, as part of an assessment of the building’s whole life carbon.
The building was aiming for the London Energy Transformation Initiative (LETI) standard target for large residential developments, with an operational energy target of 35 kWh/m2/year. UK building regulations use carbon emissions as the basis to determine compliance. LETI believes that the operational energy of a building is the main metric that should be used instead.
A fabric first approach means enhancing the performance of the building envelope through improved U-values and better airtightness. For example, the U-values of the building elements were some 55% to 60% better than the limiting U-values in Approved Document L2A. Fabric first was essential for meeting the 35 kWh/m2/year target, as energy savings from renewable technologies would not count.
Nevertheless, the proposed specification included enough renewable technology to deliver a nearly zero carbon building overall. An ‘electric only’ approach was adopted to move away from fossil fuels and their associated emissions, and benefit from the decarbonisation of the national grid.
Another difference in the specification was tackling unregulated energy demand (like equipment, lifts, and cooking appliances) that is not addressed by national building regulations. Unregulated energy can vary considerably by building type, being up to 50% of total operational energy.
Not considering unregulated energy at a regulatory level typically leads to drastically different consumption in reality compared to that estimated at the design stage. The DSM carried out for the barracks building included unregulated energy loads as part of the total energy consumption and showed the comparison with the LETI target was accurate.
“Crucially,” says Brandon, “by looking at regulated and unregulated energy, the proposed building design was about as sustainable as you can get.
The shift towards measuring whole life carbon and achieving net zero is happening across all areas of the construction industry. For a business like Rollalong Offsite Construction, manufacturing buildings offsite is attractive for clients because it reduces the emissions associated with traditional on-site construction processes.
However, taking on board that manufacturing serves to increase the company’s own carbon emissions – and those emissions are still effectively part of each project the company works on.
“Our clients, including the MOD, look to us to see what we are doing within our own operations,” says Roger. “We’re an office and factory, handling materials and logistics. They want to know that we’re on the same journey as they are.”
Brandon explains how Darren Evans was able to use the building modelling exercise to advise Rollalong Offsite Construction on how they could reduce the extent of those emissions. “As an offsite manufacturer, they bear a lot of the emissions that would normally be associated with on-site construction. Their product is a complete building, which is carbon heavy. There’s a lot of embodied carbon coming through the factory, so their scope 3 emissions are much greater than their scope 1 and 2 emissions.
“We therefore used our building energy modelling and whole life carbon assessment for the MOD tender as the baseline for an embodied carbon reduction plan for their organisation.”
Rollalong Offsite Construction have therefore implemented a plan at their own site which will involve insulation being installed to buildings, a move away from gas generally, exploring the use of solar PV, and shifting all vehicles to electric from fossil fuels.
Changes will be adopted over time, taking advantage of maintenance and replacement cycles, as part of the company’s overall approach to planning for the future.
“We look to build sustainable, long-term relationships, and it shows our clients that we take our responsibility to the planet seriously,” says Roger. “We’ve worked with Darren Evans for three or four years now and they are very much on the same page as us. Demonstrating that we’re on the road to net zero gives our clients confidence that we’ll be here in the future.”
A portfolio of building designs that perform rather than just comply, and a clear pathway for Rollalong Offsite Construction to reduce their carbon emissions.
“As an offsite manufacturer, Rollalong Offsite Construction bear a lot of the emissions that would normally be associated with on-site construction. Our building energy modelling has served as the baseline for the entire embodied carbon reduction plan for their organisation.” - Brandon Wipperfurth, Senior Sustainability and Energy Consultant at Darren Evans.
Testimonial text: “We look to build sustainable, long-term relationships. We’ve worked with Darren Evans for three or four years now and they are very much on the same page as us. Demonstrating that we’re on the road to net zero gives our clients confidence that we’ll be here in the future.”
Roger Sitch, Head of Design and Technical Compliance
