Construction system

So it probably appears that since my posts in December there hasn’t been much happening on the project.  That’s because most of that time has been spent exploring the feasibility of using previously blogged about Brettstapel as our construction method.  Pursuing a system no UK fabricator or contractor has used to build a house has been a time intensive process.  Architect Dan, who has been as attracted as me to the sustainability qualities of the system, and I, did manage to establish that it was possible to put together a supply chain.  We were able to source appropriate domestic timber, we had a company in line to mould the timber, we had expert support – and thanks should go to Dainis Dauksta of Woodknowledge Wales and Deb Turnbull of Edinburgh Napier for their help – but we couldn’t get a fabricator/erector to consider taking on the task at a reasonable rate.  Perhaps understandably given the innovative nature of the product we found that people either didn’t want to touch it or they wanted to attach a considerable premium to it.

That’s not to say there aren’t companies interested in pursuing this system.  It was interesting to learn for example, through the Brettstapel Network at the Edinburgh Napier Centre for Offsite Construction + Innovative Structures about MAKAR, a closed panel timber frame specialist who are looking to integrate Brettstapel production into their conventional manufacturing processes.  In reality though for Brettstapel to become a more mainstream option it is going to need a great many more forward thinking companies to get behind it, and for a more projects, and certainly initially those with more accommodating budgets than our own, to consider specifying it.  I continue to hold the opinion that it is a fantastic system with excellent sustainability credentials and is therefore to be much encouraged.

Our thoughts are therefore turning toward a more conventional timber build system.  Intriguingly Mark Siddall, another north-east architect, who was behind Steel Farm Passivhaus, and who I heard speak at Ecobuild, is of the opinion that on the whole you should use whatever system and materials local contractors are familiar with, which in the north-east is masonary.  I can’t say I’m convinced by that.  If we are to take a holistic approach to sustainable building then the embodied carbon of the building fabric has to be given consideration in which case timber frame will inherently be more attractive than masonary.  Cob, straw bale etc. could come into consideration but given what we’re trying to achieve in terms of a contemporary open plan living area within a vaulted roof sapce they just don’t seem practical.  A more standard timber frame obviously has its benefits.  People are obviously more familiar with it giving a wider choice of manufacturers/contractors which in turn should translate into lower costs though initial estimates from one or two timber framers suggests this isn’t a given.

I’ve always been attracted to structural insulated panels (SIPs) as a system.  They’re extremely simple as a concept.  Structural panels are formed by sandwiching insulation between two layers of wood sheet material, typically OSB eg. Kingspan Tek.  They lend themselves to creating very low u-value walls, with their large spans and uniform nature aiding in the attainment of very good airtightness levels.  Cut to precision off-site they seem to lend themselves to a quick and efficient construction on-site with minimal material wastage.  I am though struggling a little to determine the differences between the insulating cores used by different manufacturers and I’d want to do a little more research before settling on this route.

A further option, brought to my attention again by our visit to Ecobuild is a hybrid system like Val-u-therm that takes advantages of the benefits of both timber frame and SIP panels.   As with SIP panels Val-u-therm is able to deliver very low u-values – all the way down to .09W/m2K in fact – and enable very airtight construction.  One particularly attractive quality of this hybrid system is that the timber studs used internal of the sandwich sheet materials allow longer spans than the conventional SIP which could be particularly useful in terms of the creation of our contemporary open plan vaulted roof living space.  Additionally the insulating material used in the val-u-therm is a bio-based polymer derived from recycled vegetable oil giving reassurance that the insulation is environmentally considered too.

In summary, pros and cons to each; a decision will be made no doubt when the current cost estimates are firmed up…

Brettstapel

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.

BRET 1Brettstapel Wall

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!!!