It is always very productive and a change of scene; to get the Building Tectonics team out of the office together to learn more about particular areas that we work on. So, on Thursday 14th March we all went on a trip to Kingspan Potton, based in Great Gransden, Bedfordshire who specialise in fabricated timber frame housing.
The walls, floors and roof of the houses are fabricated in large panels in their factory and are then taken to site and bolted together to construct a house (or other types of buildings). Although there are several companies who already work in this area; Kingspan have moved away from the mass housing market and instead of supplying the larger house builders, now just supply one or two units to small developers or even one-off houses.
On arrival the BTL team were greeted in the meeting room by the National Sales Manager; who gave a presentation about the different products they produce and then showed them around the factory where they are made. They saw how the process works from start to finish; from when the wood comes into the factory to when it leaves on the back of the lorry. Following this, they drove 15 minutes away to the Potton Self-Build Show Centre in Little Paxton, near St Neots where they have 5 show-houses. The team had the opportunity to look around the show-houses; which showed them the different materials that Kingspan manufacture and the different structures that they are capable of producing.
Kingspan can help with the design of any house and have a pattern book of designs you can choose from; but obviously being an Architectural Practice, we already do the design for our clients. However, Kingspan can take our bespoke design plans and prepare “shop drawings” showing the panels so that they can then be fabricated in their factory. It was very interesting for the BTL team to know all about the process and the types of systems available; for those occasions when a client wishes to have a timber frame house.
There are alternative systems available from other timber frame fabricators: –
Open Panel Systems
The majority of timber frame companies use an open-panel system for the internal loadbearing of the cavity wall. These are made in a factory from a softwood timber frame covered with a structural sheet material such as plywood or oriented strand board (OSB) and fixed into a structure on-site. They have a waterproof membrane on the outside and are left open on the inside. The windows and door frames are fixed on-site and when the house is watertight; the electrical and plumbing casing is installed and the insulation put in place finished off with a vapour-proof barrier and plasterboard.
Closed and Advanced Panels
These systems are used by most of the Scandinavian frame companies and are delivered fully furnished and insulated, with the services in and the windows and doors already fixed – with the advantage that it is an airtight structure that needs minimal on-site work. However, it does mean decisions need to be made early on in the design about services and outlets.
Green Oak Frame
This is the most traditional timber-frame building method and is often referred to as exposed timber frame. The oak is often jointed using mortise and tenon joints, draw-pegged with tapered oak pegs and then integrally braced with curved oak bends jointed into the frame. Insulating panels are then infilled into the massive oak skeleton and it is made waterproof using a system of perimeter trims and water bars; before being rendered on the outside, leaving the timbers exposed.
Structural insulated panels (SIPs) are high-performance building panels used in floors, walls, and roofs and are typically made by encasing a core of rigid foam plastic insulation between two structural skins of OSB, but other skin material can also be used. The panels are manufactured under factory-controlled conditions and can be custom designed for each home. SIPs are fixed to the outside of the timber frame, so the entire frame can be exposed in the interior or covered up, depending on the look you want to achieve.
Kingspan are first and foremost an insulation company and therefore, have naturally moved toward the highly insulated end of the market. Timber frame housing can be extremely well insulated and this form of construction lends itself to the addition of a lot of insulation without making the walls unduly thick (unlike brick and block walls). However, the really interesting development is the SIP technique as these panels can achieve incredible levels of insulation and therefore, are often found in zero energy projects where no heating is required; other than the heat that is created by simply inhabiting the house (possibly with the addition of some solar heating).
Building Tectonics have designed a couple of very low energy houses and are greatly interested in this area. SIP panels also offer really low air infiltration so therefore, help reduce heating bills and increase comfort as they avoid drafts and cold spots. They can be very strong and rigid and can be used in floors and roofs; which is a real game changer in the construction of houses, but the building industry has generally not embraced this new technology. Houses built like this can be erected on-site superfast incorporating all the services and the standard of finish can also be superior.
As a practice we would like very much to use this technology wherever we can; but the question is whether our clients will choose something brave and new. The major practical difficulty is using prefabrication techniques for extending existing buildings, which is where most of our work lies. Ironically, the big problem would be bolting something so perfectly made (1 or 2 mm accuracy) on the side of an existing building where the building tolerances can often be measured on several centimetres. What we need are clients who can see the benefits of such new techniques and we stand ready to help in any such project should it arise.