South Yorkshire Housing Association manages 6,000 homes to provide social and affordable rent housing for over 10,000 residents (SYHA, n.d.). The housing association is helping to lead the way in less conventional construction methods, utilising industrialised construction to deliver a portion of its homes. As a founding member of the Housing Off-Site Alliance (OSHA, n.d.), SYHA is also part a framework and network of registered housing providers, local authorities, contractors, and strategic partners, dedicated to delivering high-quality, affordable housing produced using both 2D panelised and 3D volumetric approaches. The two semi-detached WikiHouses, with an approximate floor area of 70m², are situated in Sheffield, close to the city centre. They were delivered in collaboration with product design providers Open Systems Lab, architects Architecture 00, engineers Momentum, manufacturers Chop Shop, and assembly and installation were carried out by Castle Building Services supported by Mascot Management. The project is not only exemplary in reducing embodied energy in housing but also proves to be energy efficient, having earned runner-up in the Ashden Awards for Energy Innovation. Design WikiHouse aims to democratise housing with the creation of standardised and open-source designs incorporating industrialised construction, based on foundational principles such interoperability and a lean approach inspired by the Toyota Production System (WikiHouse, n.d.-a). WikiHouse provided SYHA with a “jigsaw of pieces” in the form of panelised components designed to be assembled around a framing system. The system was made from simple plywood construction, with no need for steel due to the proposed low building height. Timber is not only ideal for buildability and deconstruct-ability as a lightweight material, but it also possesses carbon sequestering properties. It should be noted the open-source product can be limiting for some adopters of WikiHouse as additional design, construction and installation services are not included. SYHA therefore needed to fill the gap between the product and delivery to their end-users. Manufacturing WikiHouse products lend themselves to self-build construction or utilisation of ‘micro’ factories. SYHA’s pilot used localised construction to manufacture the plywood frame using digital files, cut by CNC machining company ‘Chop Shop’, located just 1 mile from the site (Plowden, 2020). Cutting the pieces was a fast and efficient process, which was designed to minimise material waste. Chop Shop also assisted by storing the building parts until the site was ready for assembly due to the lack of on-site storage space. WikiHouse seems to be well suited to manufacture by a distributed network of small manufacturers. However, according to SYHA, there is potential for scalability with larger housing association schemes in future. In addition, the production strategy is ideal to unlock small, tricky sites within the housing association’s portfolio, facilitating the production of high-quality housing with high circularity potential. Transport and assembly The dimensions of the timber frames were small enough to be delivered to site using a transit van rather than a larger lorry, which proved to be more manageable and cost effective. Once on site, the prefabricated building parts were assembled “like a jigsaw” using a step-by-step manual, although SYHA felt the instructions could be enhanced in the future to improve delivery by a range of stakeholders (Plowden, 2020). The project programme was much shorter compared to a traditional build, the first home was manufactured and assembled in under a month. This process was even faster for the second home due to the experience gained from the first home, highlighting potential to improve efficiency for larger schemes in the future. As prefabrication and assembly are still unconventional, the transition between these processes may present additional complexity for the stakeholders involved compared to a traditional build. In the case of SYHA’s WikiHouse, Miranda found “the manufacturer saw its job as providing the cut pieces for the installer to install, they didn't appreciate that they were part of a manufacturing process with the installer”. She went on to highlight that manufacturers and installers are typically separate parties in the UK, with installers often being main contractors who aren’t used to off-site methods. The team also had to overcome issues with unexpected ground conditions which hadn’t been included within the original site survey, though this was unrelated to the construction system used. Building performance SYHA’s WikiHouse homes have so far proven to be warm and energy efficient, resulting in low energy bills for residents, owing to the high-level of insulation within the plywood structure and panelling. The building strategy ensures easy maintenance and access during the use phase without disturbing residents. This was achieved by incorporating exterior services coupled with dry construction techniques. As a result of their involvement in the whole process, SYHA is able to effectively manage disassembly for future maintenance and potential adaptations, as their Home Maintenance Team were able to observe how the WikiHouses were assembled. Legal Providing the design and detailing are correctly implemented, meeting UK building regulations is not an issue with the WikiHouse system, which claims its products will exceed the requirements of UK building regulations (WikiHouse, n.d.-b). However, it proved more difficult to obtain the building warranty for the SYHA pilot. All new products need to be warranted, which requires warranters to inspect the whole building process to guarantee the necessary requirements are met. SYHA’s WikiHouse utilised the Buildoffsite Property Assurance Scheme (BOPAS) (n.d.), which is a specialist warranty provider for buildings using industrialised construction, referred to as Modern Method of Construction (MMC) in the UK. Homes with BOPAS accreditation are readily mortgageable for a minimum of 60 years. Financial Using an off-site approach can be financially advantageous, as more time is invested upfront to plan, design, and manufacture. This shortens the time spent on-site and therefore reduces preliminary costs for the operation of the construction site. Although the project benefitted from a shortened timeline due to the industrialised approach, the WikiHouse system ultimately proved to be more expensive than a traditional build. According to Miranda, the cost of the completed homes was approximately 33% higher than a traditional build but she estimates if they were to build using WikiHouse again - taking on-board lessons learnt - the premium would reduce to 12% (Plowden, 2020). However, there is hope for the WikiHouse system to become a more financially competitive alternative to traditional build in the future. For this to happen, Miranda suggests improving efficiency of the assembly process, particularly with faster utility connections. Additional financial viability could also be achieved if the system were to be applied to larger sites. In regard to a life cycle costing approach, Miranda believes it is too early for SYHA to say whether the WikiHouse pilot will prove to be cheaper than a traditional build in the long-term.