A modern innovative low carbon housing system
Professor Pete Walker
BRE Centre for Innovative Construction Materials
Department of Architecture and Civil Engineering
University of Bath
The BaleHaus is made from timber and straw bales with a lime render.
Total carbon contribution from existing and new buildings is around 50% of the UK’s footprint, of which around one third of the total can be attributed to the housing sector.
Construction industry is responsible for around 10% of all UK greenhouse gas emissions.
Embodied Carbon and Operational Carbon
This is about how maintenance of a building can have an effect on carbon emissions.
A building is designed to survive 30 to 60 years (although there are people living in older houses).
In ten years the aim is for houses that will have a lifetime of 300 years.
Passive buildings will reduce operational carbon.
The term passive house refers to a rigorous, voluntary, standard for energy efficiency in a building, reducing its ecological footprint. It results in ultra-low energy buildings that require little energy for space heating or cooling.
Opportunities for renewable materials in buildings
Will reduce greenhouse gas emissions;
Will lower embodied carbon (stored carbon);
Provides a chance to improve building performance;
Will allow resources to be used more efficiently;
Will allow the replacement of non-renewable materials;
Will reduce waste;
Will produce healthier buildings;
Will open up new agricultural markets;
There could be one problem with passive buildings in that windows can’t be opened. This could mean a build-up of chemicals. Putting in ventilation would increase the cost.
Renewable Building Materials gaining recognition
Prefabricated straw bale construction winner of two awards (Offsite and Sustain magazines)
The last labour government was a big supporter of low carbon housing and Kevin McCloud got on board the project. He opened the building in 2009.
Kevin McCloud (born 8 May 1959) is a British designer, writer and television presenter best known for his work on the Channel 4 series Grand Designs, which he has presented since 1999.
In early 2007, McCloud led a consortium to purchase two plots of land to build a HAB housing development on the outskirts of Swindon, Wiltshire. Design work for the highly sustainable buildings began, with a planning application scheduled for May 2008.
In October 2009, it was announced that Hab Oakus, a joint venture between Hab and housing group GreenSquare, had won planning permission for its first housing scheme in Swindon designed by Glenn Howells. Construction of the development was completed late in 2011. The process was filmed and broadcast as part of a Grand Designs special two-part episode called Kevin’s Grand Design.
At the start low carbon housing will cost more. Timber needs to be adequately protected and architects and builders need proper training.
There is also the time for the raw materials to be grown to consider.
The production of masonry emits around 110 kg of CO2/m2 for an external cavity wall but a straw bale stores around 145 kg CO2/m3 (70 kg CO2/m2 for a 490 mm thick wall).
Renewable construction materials in the UK
Timber and timber based products
Natural fibre insulation
Hemp, flax, wood fibre
Geotextiles, fibre reinforcement
Hemp is a commonly used term for varieties of the Cannabis plant and its products, which include fibre, oil, and seed
Unfortunately in the UK our trees grow too quickly for construction purposes so we would have to import the wood. Fast growth means they are weaker.
Stadthaus is a nine-storey residential building in Hackney, London. It is thought to be the tallest timber residential structure in the world. It was designed in collaboration between architects Waugh Thistleton, structural engineers Techniker, and timber panel manufacturer KLH.
It was constructed very quickly.
Straw bale construction
Straw is an agricultural by-product; the dry stalks of cereal plants, after the grain and chaff have been removed. It is not the same as hay, which is usually grown for grazing livestock.
Straw has the advantage of not being very flammable.
The above right picture is of Pilgrim Holiness Church in Arthur, Nebraska
This was developed in Nebraska, USA in the late 1800s because it was the only material readily available. The technique declined with availability of ‘modern’ industrial materials. Steel is 200000 times stiffer than straw.
Straw was used for other things such as animal bedding and a medium for growing mushrooms on. It is also a biomass source.
There was a resurgence of this material in the 1970/80s as a result of the oil crisis and the 1990s saw the first straw bale buildings in the UK
Three main types of construction:
Post and beam with straw infill
Low thermal conductivity
Low embodied carbon
Co-product of cereal production
Locally and widely available
Low strength and stiffness (but still suitable for low-rise load-bearing applications)
Poor fire resistance
Full of bugs and vermin
Only suited to self-build/hippy market
Little strength – wall hangings
Unsuited to mainstream construction
Modern straw buildings
If straw bales are such a good building method and material why aren’t there more straw-bale buildings being constructed?
“The bottom line is it’s just too messy and inexact a technique to be put into widespread, mainstream use. There are too many ways to do it, too many variables and inconsistencies. From getting the bales (which are always differently shaped, sized, weighted and priced) to the different kinds of framing, plastering, etc, the whole process is well suited to owner-builders or committed professionals, but not so friendly to the person who just wants to build some houses for a living, or the developers who want to hire them to do that. “ Chris Magwood, Canadian straw bale builder
ModCell prefabricated straw bale panels were used to build the BaleHaus.
The aim was to reduce carbon dioxide emissions from construction and operation of new UK houses.
Renewable materials (materials for sustainability goals and to be affordable) used included timber framed panels and straw bale infill.
The building was designed to be dismantled, reused and recycled. In fact it has been moved from its original position.
Low-energy standards of PassivHaus were aimed for. This means a reduction in the requirement for space heating and cooling, whilst also creating excellent indoor air quality and comfort levels.
ModCell stands for modular cellulose.
Pre-cut engineering glue laminated timber from Switzerland, manufactured to strength class C24 as outlined in European Standard EN 338:2003
K39 lime render provides a breathable layer on the walls.
Lime render is a lime-based cementitious mix applied to the external surfaces of traditionally-built stone buildings. It allows the building to ‘breathe’ – as lime is porous, it allows for the collection and evaporation of moisture. Cement in contrast, an often applied render for stone buildings, traps moisture behind the stonework, which may result in the erosion of the stone masonry.
Glued laminated timber, more commonly known as Glulam, is a type of structural timber product used for load bearing structures. The product is composed of several layers of dimensioned timber glued together.
Ideally it would be good to do without the steel but it is far more efficient at bracing the building. The cost of the building can be roughly divided up as 30% timber, 30% lime and 30% people.
In terms of monitoring the layout is like this…
Ground floor First floor
The bedrooms are on the ground floor for thermal stability.
-The ground floor panels of the BaleHaus at Bath were constructed in a ‘flying factory’
-The ‘factory’ was located in a barn, hired for the offsite construction period, on a farm approximately six kilometres from the site in Southstoke.
The term “flying factory” is given to something that is set up to make things for something that is less than ten miles away from it.
Below is a link to another “flying factory”
The timber was pre-cut and pre-drilled and brought in from overseas. The picture above right show the assembly of the pre-cut engineered glulam timber from Switzerland.
The picture below left shows that corner and vertical steel bracing bars are secured in the frame to provide structural strength.
The picture above right shows that stakes are then placed in the base of the panels and are used to keep the first layer of straw bales in place.
Stakes are added at two further stages of the bale infill, again to add stability to the panel. Broom handles are used to place the straw bales giving a constant 430mm gap between them.
Six layers of bales are fitted into the panels before being compressed using a tractor or fork lift to enable the final layer of bales to be squeezed in.
The straw bales are then tapped into place to create as vertical a surface as possible. The steel bracing is then tightened and the final stakes are added to the top and sides of the panel.
The straw bales are then trimmed to create a smooth surface for application of the render. Lime render is applied by spray, in three coats. This then needs to cure for 14 days before the panels can be moved.
The building was weather tight in three days. The building was begun in May 2009 and was finished in September 2009. The building was was slowed down a bit because of the window doners.
The corners were box sections filled with straw. A fishplate is used to keep the layers of insulation together.
The wood is treated to maintain the colour. The lime can be painted.
The building is above the ground. It sits on a high ash content timber slab which in turn sits on a concrete base.
32mm of lime render does allow some water to get in but it also lets it escape.
BaleHus is not a passive house.
Inside the BaleHus
Above right is Ms Sarah Edwards in the kichen. Like me, she was one of the Goldsmiths’ course participants.
Laboratory testing: Structural; Thermal; Acoustic; Fire
Monitoring and testing of BaleHaus; Durability; Thermal performance;
Structural Testing Phase 1
Investigating the effect of wind. High winds could crack the render. The panels could withstand a lot of force.
Structural Testing Phase 2
What force can cause cracking?
Structural Testing Phase 3
Vertical pull out test on 3 types of joint: Screwed connection; Dowel connection; Dove tail
During structural testing carried out in a previous project, the corner joints in the frame were shown to be a limiting factor.
The racking load is applied to the top frame element and is transferred through the joints into the sides of the frame and then to the base.
Under loading the top of the panel tends to lift and the joints get pulled apart.
Investigation on 3 different types of joint carried out to establish which is best, screw connected, dove tailed or dowel connected.
Base of the joint specimens were fixed to the floor, with the other part of the joint being loaded.
Racking Shear testing
4 ModCell panels were constructed using the screw connected joints.
2 of the panels were full 3 bale wide panels and 2 were 2 bale wide with a window opening.
The panels were secured to the floor and an in plane load was applied to the top corner of the panel. Load and displacements were measured.
Racking Shear testing – Conclusions
Three bale panels similar
Two bale corner braced stiffer due to vertical reinforcement
Three bale stiffer than two bale
The different bracing systems in the 3 bale panels made little difference. A cross brace is a more efficient way of bracing and one would imagine that this would perform better. But it does not use any of the large timber section to resist the loading. The corner bracing does, and therefore both perform similarly.
In the 2 bale panel the cross braced panel is less stiff. This is because it does not have any vertical reinforcement which resists the lifting of the top element.
Additionally to structural testing a computer theoretical computer model has been developed.
This will be used to predict the behaviour of the panels when different elements are changed in order to see if it is worth while doing full scale structural tests.
The graph shows the results from the structural testing and the results from the model. As you can see up to the serviceability deflection limits the model matches the test results.
The model is limited at this time as it is only linear elastic and does not allow for cracking of the render.
Testing for thermal transmittance
Testing for acoustic transmittance
Red hot timber and straw
Credit Chris – Carbon Connections project
Over 1000°C for 2 hours 15 minutes, without failing. 90 minutes until lime render fell off and then another 45 minutes without the lime render. 30 minutes was required for the entire test.
Fire test in accordance with BS EN 1364-1:1999 > 1000°C 2 ¼ hours
Durability of straw bales
Above right shows data acquisition and recording ‘Squirrels’
Monitoring of the BaleHaus
66 wireless sensors recording temperature and relative humidity
Thermal performance: Seeing how much heat is lost through windows and doors. Efficiency of 0.6 is desired for a passive house.
Occupancy monitoring – People are simulated in the building by lightbulbs
Testing on BaleHaus
Tests on house:
Performance requirements: Structural safety; Environmental performance; Durability
Quality assurance; Materials and components; Manufacturing process; Installation
British Board of Agrement (BBA)
National House Building Council (NHBC)
Local Authority Building Control (LABC)
Inspire, Bradford, 2012
Hayesfield School, 2012
Hayesfield Girls’ School is an all-girls secondary school with a co-educational sixth form located in Bath, England.
LILAC (Low Impact Living Affordable Community), Leeds
UK’s first affordable ecological cohousing project
University of Nottingham, 2011
Will Beazley, Sophie Hayward, Graham Mott, Neil Price, Brian Purnell