Technical Editor Bruce Meechan calls on a Coventry business that is taking modular construction to a new level.
For anyone who didn't manage to make it to The Offsite Show at London's Excel Centre in October, and therefore missed the chance to tour Offsite Housing (UK) Ltd’s highly impressive show home - there is still plenty of time to see the two bedroom affordable family house. Furthermore, without the height restrictions imposed by the exhibition space, the two modules and roof capping have been erected together on pad foundations at the parent company's premises in the Midlands.
Central Site has been at its present location at Binley in Coventry for a decade; since when it has established a formidable reputation for delivering high specification, cost effective modular accommodation for clients across the education sector. Now, however, it is planning a move into new 100,000 square feet premises nearer Birmingham, from where the management team is expecting to realize its long held ambition to make an impact in the residential market.
Well before its participation at Excel, Central Site had already been involved with a number of residential accommodation projects and – just prior to the recession – built a terrace of three trial homes.
Unafraid to back its certainty over the quality of the offer, the company funded the build entirely itself, and these are still rented out today so that it is able to judge the long term performance and durability of its solutions.
That pilot scheme, combined with the company’s vast experience of manufacturing modular volumetric buildings for schools and colleges of all scales, has brought it to a position where Managing Director Mike Walsh is more than confident in the ability to supply small to medium size residential developments. Indeed the new factory will raise its capacity to around 1000 units a year.
Mike comments: “We have the vision of being able to produce a house that is no different in appearance or feel, from any traditionally built property on a typical volume development. But we can deliver it to site in the form of fully fitted out modules, and complete the erection in a single day.”
In fact Offsite Housing is currently capable of erecting eight or more units a day using a single crane: installing them onto prepared footings. These could be pad foundations, piles, ground beams or perhaps a raft if ground conditions dictate it. Meanwhile the only building work left to do on-site - aside from fitting a section of banister - are to fix a couple of rows of tiles where the ‘top hat’ attaches onto the upper storey, and the final courses of Corium across the elevations.
The choice of tile brick type, Corium - manufactured by clay product specialist Wienerberger – rather than a less substantial brick slip system on the show home is typical of the company’s ethos on specifying substantial, high quality components.
Clients could of course choose to have a render finish or lightweight cladding, but Mike Walsh believes social housing providers will be attracted by the robustness and absolute minimal maintenance which Corium offers.
Inside the walls are all lined with British Gypsum’s Rigidur, fibre reinforced boards which are also capable of resisting long term heavy usage; while also offering a very solid fixing. The entire feel of the modules, even before they are erected, is one of solidity and permanence.
Their construction is of a galvanized structural steel frame with corner posts and beams which form the modules; enabling them to be stacked up to six storeys high.
The floor construction begins with the fixing of an OSB layer, followed by high density rock mineral wool, and can feature underfloor heating loops if desired by the client. Over this the assembly team lays a floating floor of interlocking, 28mm thick gypsum fibreboard panels which offer the same feeling of substance as a conventional concrete floor. The same construction features for the first and any further, intermediate floors, but containing acoustic rather than thermal insulation.
The exterior walls, with their semi-rigid glass fibre wool infill and over-lining in EcoTherm PIR insulation preventing any cold-bridging of the galvanized steel members – what Mike Walsh describes as “Structural wall panels inside structural frame” – completes a highly insulated and airtight construction which is also very rigid. The latter is of major importance in preventing any damage during transport and installation. Crucially, customers are spared any “snagging” operations once the erection team departs at the end of the day.
Mike Walsh emphasizes: “Aside from the service connections, the homes are ready for occupation when we leave site. From a housing association’s point of view this means they benefit from a radically shorter build programme once the infrastructure is in, and much earlier revenue from rent. It also means properties aren’t sitting there for weeks or months, exposed to the risk of vandalism, while they are being fitted out.
“We take care of all the design for fabrication, which is covered by accreditation, and can even offer a choice of standard house types starting from two bedroom accommodation, which can avoid the client paying relevant architects’ fees. We are also close to obtaining warranty and insurance cover and all of the components we use have BBA certification.”
One of the benefits of achieving very low U-values and airtightness figures in the region of 2.5 m3/m2/hr is that space heating demand is also relatively low; which will appeal to RSLs wanting to keep their residents out of fuel poverty. In turn this has enabled the company to build a long term relationship with air source heat pump manufacturer, Mitsubishi Electric.
Not only can the Ecodan high efficiency heat pumps be found running successfully at the vast majority of its education sites, one was also located alongside the show home at Excel; and is keeping the two bedroom home very warm now.
Mike Walsh concludes: “The relationship with the client is flexible: we could take on the entire project – offering a turnkey solution – or the modules can be designed, manufactured and delivered under a framework agreement. Also any size or architectural style of property is possible, fitted out right down to the carpets and curtains if required.
“We believe because of our experience in other sectors, that we are ahead of a lot of the competition: in terms of the quality of our offering, our design capabilities, as well as various KPIs and our unbeatable speed of erection. Furthermore we can offer this at rates competitive with traditional build and currently we are in contractual negotiations with Housing Associations on numerous projects.”