I’d like to write early on about our preferred method of construction – Brettstapel. I say preferred because there is still a considerable amount of feasibility work to be done before being able to say with any confidence whether we can actually use it. Whilst it is an established method in Germany/Austria/Switzerland it is not so here in the UK (though it ought to be!). Brettstapel is a simple solid timber construction; softwood lengths are stacked side by side and connected together using hardwood dowels. Needing no nails or glue the system works by using dowels of a lower moisture content than the softwood lengths. Over time the dowels absorb moisture in order to achieve equilibrium, in the process expanding and locking the timbers together creating load bearing-structural panels.
As the video touches on, the benefits of Brettstapel are many. It has excellent structural properties and has been utilised in hotels, industrial buildings and bridges. It offers too all the benefits of off-site prefabrication, with savings from the refinement of the manufacturing process and ease of erection on site. The accuracy of manufacture it affords also means extremely high standards of airtightness are easily accomplished. It also has very good fire resistance properties (a property many erroneously don’t associate with massive timber).
What makes Brettstapel such an attractive prospect however, and for my mind gives it the edge over so many alternatives, is its environmental qualities. The amount of timber used means massive amounts of carbon dioxide are sequestered, “locked-up”, in the building. The structural nature of the panels means that much lower grade timber than is usually used in timber frames can be employed. This means rapid growth species, such as Sitka spruce, can be easily used which is beneficial for the carbon sequestration process and simultaneously gives a high value output to what is normally a low-value product. With no glue being used in their manufacture, and the timber of the panels forming the internal finish, Brettstapel also contributes to a very healthy internal environment with no hazardous compounds, or VOCs, released as there are with other systems. The internally exposed timber via its moisture transfusive and hygroscopic properties further benefits the internal air quality by assisting in maintaining ideal levels of humidity.
All in all, with appropriate sourcing, it appears a fantastic systems from a sustainability point of view. Clearly such a system will be more costly than conventional timber frame, but just imagine if we were able to turn our housing crisis into a climate solution! In my mind I can’t see with the right controls why this system shouldn’t qualify for carbon credits? The additional financial cost to the developer could be offset by the ability to sell credits on the back of the sequestration of carbon to those looking to offset their carbon emissions, just as some forestry is planted for offsetting purposes. Anyway, perhaps it would be sensible to concentrate on the house for now. Indeed if we are able to pursue our desired intention and use domestic timber in the manufacturing process this will be the first house in the UK to do so. There is a house in the Scottish Borders, Plummerswood, which used Brettstapel sourced from Austria, and there is a visitor centre in North Wales, Coed-y-Brenin, which used domestic timber in locally manufactured panels, but as yet no residence which does so. We will have to source and assemble our own supply chain and even then the final cost is extremely uncertain so it is going to be no small challenge!!!