These days, innovations in timber frame are a bit thin on the ground. I-beam walls, SIP panels, Filled cell walls, Twin walls, Icynene and Warmcell insulaion, Metal Web or I-beam joists and roofs, Glulam, Douglas Fir and Green Oak post and beam structures and so on are all fairly well understood. But now BATT has added “Tradical® Hemcrete®” to its range of timber frame options
“Hemcrete®”. That’s the name given to a near dry mix of lime and chopped hemp that has some amazing properties, although one of them is not structural. This is the role reserved for BATT’s timber frame. In combination the two are used to create an exciting, highly energy efficient external envelope, that exhibits many of the characteristics of masonry – but better.
As Environment Minister Phil Woolas notably predicted at February;s Ecobuild, “In the next twenty or thirty years, we won’t be using concrete and brick.” Instead he singled out lime and hemp composites as particularly praise worthy, believing that such alternative renewable materials and technologies will kill off these better known industries before long.
And in this he is in good company. CEO of the Benfield ATT Group, Professor Dr Michael Benfield had been monitoring the benefits of Tradical® Hemcrete® (TH) for 2 or 3 years – and waiting for it to achieve BBA status. This accomplished the Group was fast off the mark to team up with Lime Technology, who supply the Hemcrete mix, to satisfy the environmentally sustainable development ambitions for one of its developer client’s for an advanced design Code 5 housing project in North London. Since, uniquely in the timber frame sector, the BATT group are Chartered Building Consultants, Chartered Surveyors, and LABC partners, the fact that TH is also LABC approved was a major deciding factor.
So Why Is TH So Special?
Well, to start with it ‘locks up’ CO2. And with the construction and use of buildings accounting for a staggering 50% of all CO2 emissions in the UK, that’s a big deal. Especially when bricks, blocks, concrete, steel and many other building materials are responsible for several million tonnes of the stuff every year.
The Blight of Bricks
In fact studies have shown that up to 100kg of CO2 is emitted in the production of each square metre of masonry walling for houses. That’s around 20 tonnes of CO2 in the walls of an average house alone.
A Growing Solution
Conversely, if you plant a hectare of hemp and wait 14 weeks you can harvest enough to build a house offering a carbon footprint that’s lower than zero. That’s the root of the environmental case for hemp and lime-based Tradical® Hemcrete® and one reason why it is increasingly becoming the material of choice.
Less Than Zero Carbon
As one of the UK’s few Chartered Environmentalists in the construction sector, Prof.Benfield notes the critical acclaim received by TH from all sectors of the built environment. “Cast in situ or even spray applied, this bio-composite thermal masonry material creates ‘less than zero carbon’ sustainable structures” he comments. “It locks up around 110kg of CO2 per m³ of wall and, combined with BATT’s specialist timber frames, provides one of the best value structural solutions for low impact, sustainable and commercially viable construction”.
Besides neutralising, or even reversing, the harmful Greenhouse Gas effect of normal masonry, (hemp captures carbon dioxide during its rapid growth, releasing oxygen back out to the atmosphere) TH offers fantastic thermal efficiency as well as high acoustic insulation, low density, excellent water vapour permeability, and high flexural strength.
Delivering a balance of insulation and thermal mass, these walls provide a thermal inertia which prevents changes in outside temperature (e.g. overnight frost) from influencing the internal temperature. Energy saving is further enhanced by the resultant monolithic shell allowing excellent airtightness to be achieved.
Code Cracking Composite
Overall this means that a composite BATT timber frame + TH building uses perhaps the least energy of any structural design, especially when combined with roof as well as wall fabrics. Here Benfield have worked closely with Lime Technology in the detailed aspects of the timber frame.
Featuring an internal, rather than external, sheathing, this can be directly plaster skimmed, or otherwise decorated for fast internal completion. Externally it can receive a direct render finish, or other forms of cladding. For timber frame sceptics it feels solid - inside and out!.
|(Harvesting)|| (BATT frame+TH placement)