Here in the office we’re busy working away on a new build design for a site in Cornwall . It’s windy, rainy, cold, sunny, hot, and blustery down there, and generally all in the same day! So our natural instincts are of course, to create a design that’s as warm, energy efficient and as fast to build as possible. And one that keeps all that messy Â weather out too.
So, we’ve turned to the wonders of prefabricated design, to create a home that will stand the test of time, meet our exacting environmental standards and the client’s budget. Iâ€™ve previously worked with prefabricated SIPS (structurally insulated panel systems) on episodes of BBC DIY SOS and been really impressed by the efficiency and speed of construction, but this will be of a different scale altogether. So, with these ideas in mind I thought I’d share a little of our research into the possibilities and opportunities here in the UK.
I would like to start by differentiating between my thoughts on “kit houses” and “pre fabs”. While both are manufactured off site under factory conditions, in my mind, kit houses suffer architecturally under the delusions that architecture can be a “one size fits all” solution. Sure, “modifications” to the design of the kit house can be made. However, I’ve seen too many that miss key opportunities offered by the site due to the limitations of the kit house and the design process.
A prefabricated house uses all the benefits of offsite factory construction with the added skills that the architect can bring to the project, such as site analysis, context, originality, bespoke design and styling. The final result being a design that is efficient, cost effective, sustainable and, most importantly, unique.
Of course, every good house has to have solid walls. UK building regulations stipulate that timber frames can be as little as 140mm thick, filled with lightweight fibreglass. At that width it would be like living in a garden shed – too hot in the summer and freezing in the winter. Which is why Touchwood, a market leading bespoke timber frame company, ensures their timber frame walls are more than double that at 300mm, and packed with fireproof Warmcel (made from recycled newspapers) insulation.
Touchwood also uses Passivhaus technology,Â developed by Professor Wolfgang Feist, which reduces energy use for heating and cooling your home by 90% compared to a standard house. Utilising building techniques that prevent cold bridging, but create high levels of air tightness, the Passivhaus principle produces great levels of insulation and high levels of solar gain.
I also highly recommended that you use the Passivhaus standard windows and doors,Â which are triple glazed and cut U values down to 0.79.
Â Developed in the 1930s in the US,Â SIPS are another tried and tested form of construction. They are modern, cost effective and very energy efficient. And because they are very versatile, the panels can be used as walls, floors and roofs, both internally and externally. SIPS are constructed in a sandwich that incorporates two outer layers of Oriental Strand Board (OSB) filled with premium carbon expanded polystyrene.Â They are perfect for filling spaces between existing structures but also widely used for extensions and even whole new builds.
The nature of most pre fab or kit houses means they are produced in factories and delivered to site. But imagine if you could design and create your building on site. That’s exactly what the mobile production facility (MPF) used by Facit Homes allows you to do. The MPF converts the original 3D designs into actual physical components on site and in front of your very eyes. Every single component is produced to the design, which reduces costs and lead times. It also means the logistics of transporting your components is eliminated. All pieces are numbered corresponding to the design, making assembly that little bit easier.
Facit homes reduced energy consumption and waste (insulation is pumped in as loose material so there are no offcuts) and any spare timber is simply sent back to the supplier where it can be used as fuel to power the sawmill. And like the Touchwood system previously mentioned, they can be used in alignment with the Passivhaus principle and triple glazing system. Facit buildings are also designed to be airtight, which means warmth is preserved but also makes it necessary to have a heat recovery system fitted to draw in fresh air and dispose of stale air.
I really love the idea of a mobile factory. It means that you can use local materials really efficiently. And the fact that it tidies up after itself at the end of the job by reusing otherwise unwanted materials is brilliant, if a little pricier than standard pre fabs.
Modcell is another pre-fabricated system that uses the insulating power of straw or hemp. Bales are loaded into the ready-made panels (sizes to suit but by far the most common size is 3m x 3m x 480 mm). The frames are made using sustainably sourced material.
Once a panel is made it needs to be covered in a lime render or cladding. Then, once finished, they are strong enough to be used as load bearing panels or simply freestanding panels in a structural frame.
And one last method worth taking a look at is the Mantle systemÂ – we’re looking to use this system for a new build cafe in Brighton;Â it’s aÂ hybridÂ combination of the SIPS system and the stressedÂ skin panels. There are plenty of benefits not only in structural strength, it’s also super fast to build and of course superÂ efficient, as a designer you really just need to add a little inspiration. Check out their good explanatory video.
Thereâ€™s a lot to think about, with so many different systems to choose from. But one thing is for sure, if youâ€™re thinking about building your own home, it seems there are few better ways to do it than with a pre fabricated construction.