‘Green’ timber homes

Presentation delivered at the Institute of Timber Frame Builders 2010 General Meeting,  on 28^th October 2010

The need for  ‘Green’

We are all aware that our planet is basically in a mess:

• we are faced with the threat of unprecedented global warming, most of which is now known beyond any doubt to be manmade
•   in terms of resources we’ve reached the point where current demand exceeds supply, so we’ve started eating into our capital
• worst still, the waste we produce is polluting the depleting remaining capital, further reducing the effective balance
• we face a potential energy crises

So why should this effect what and how we build? The reason quite simply, is because the construction industry and the built environment consume:

• 50% of all resources globally
• 45% of all electricity generated to run the built environment, plus an additional 5% during construction, which in turn directly contributes to carbon emissions and therefore global warming
• 70% of all timber products

 

So the built environment can be considered the ‘low hanging fruit’ with regards improving our situation, as any improvements in the way we construct can have a real positive effect on our environment.

It is this awakening that is leading to:

•   changes in consumer awareness resulting in more eco-conscious choices
• future adaption of government policies and regulations in most developed countries with regards energy use of buildings, mostly calling for either net zero emission or carbon neutral buildings by around 2020
•   At home in SA we have the SANS 204 code, Energy Efficiency in Buildings, which while currently serving as a guideline will in the near future become mandatory

Carbon Neutral Buildings

In order for a building to achieve net zero operating emissions, it must, once built not require any more energy than it produces. In order for a building to be truly carbon neutral they need to have net zero emissions in their construction, operation and the embodied energy of materials – so while perhaps possible by 2020 with new technologies, we are still a long way off.

So, how do we go about getting closer to achieving carbon neutrality?

We start by aiming to achieve net zero operating emissions, and to do this we look at a range of initiatives and technologies such as:

• passive design
• on-site generation of energy from renewable resources
• efficient appliances & light fittings
• purchase green power (when this option is available in SA)
• optimising, upgrading or removing heating, ventilation and cooling systems

To get closer to Carbon Neutrality, we also need to consider;

• reducing the embodied energy in materials (embodied energy is all the material to produce, manufacture, transport and install a material)

Timber: a ‘Green’ building material

Why is timber considered to be a ‘Green’ building material?

• Timber is a truly renewable resource
• Timber as a material is already carbon neutral. Further than that, because of the carbon sink effect of forests, timber from sustainably managed forests can actually be better than carbon neutral (which could offset some of the non timber materials in the building)
• Using timber rather than other building materials can save on average 0.9 tonnes of CO2 per cubic metre of material used 
• Timber has the lowest embodied energy of any mainstream building material –   ¼ of that of brick and 1/5 of concrete for example
• Timber has better insulation properties (higher R-value) than most building materials; 5x better than concrete, 10x better than brick

Source: www.woodforgood.com

‘Greener’ design for Timber

While selecting the correct materials is a step in the right direction, much of what is required to achieve a ‘green’ home goes beyond just material choice. It also requires the correct design strategies.

The key aim of these is to maximise the utilisation of timber (remembering that 70% of all timber consumed is used in construction); by smart design, making the best use of properties unique to the material, reducing waste and enhancing durability. 

Making the best use of the unique properties of Timber

Timber has a high strength to weight ratio, with its highest strength running parallel to the grain. While as a material it provides considerable flexibility in design, in terms of efficiency, it performs best with clearly defined and logical load paths. The process of rational construction calls for, for example, trusses to be seated directly above first floor wall studs which in turn fit directly above floor joists which are directly lined up above ground floor wall studs.. These principles can reduce excessive lintels and heavy beams and if applied correctly, can lead to a logical clarity in the design of a timber building, particularly where the structural and loadbearing elements are exposed to view. 

When designing for energy efficiency, materials need to be evaluated in terms of their thermal properties, namely insulation and thermal mass retention properties. An important factor in favouring properties of either insulation or mass retention is the diurnal fluctuation (day night temperature variation) of a particular region – generally the further inland, away from the temperature-moderating effect of the ocean, the greater the diurnal fluctuation. Lightweight materials such as timber have high insulation values and low thermal mass retention properties while the reverse applies for high mass materials such as masonry. In coastal and other areas of low diurnal fluctuation, timber is the ideal material due to its insulation properties, as well as the opportunities afforded for insulation in the space within a timber frame wall. It’s easier to heat a timber house than a masonry house as the timber walls provide more insulation while absorbing less of the heat. In dry inland areas with high diurnal fluctuation, energy efficiency would best be achieved by including elements of high mass, such as a masonry fireplace, or concrete floors, within a timber building, which would absorb heat during the day and emit this at night, so doing moderating the temperatures and reducing energy required for artificial heating and cooling. In summer these elements of high mass act as a heat sink at night, which help to keep the building cooler during the day. This principles need to be applied in conjunction with passive solar design, by designing to shade elements of high mass in summer, and allowing them to collect heat from the low angled winter sun.

Reduce Wastage

Specification of the grade and type of timber product, and particularly the avoidance of over specification, can have a large impact on efficiencies and wastage. Timber is a natural product, each piece is unique, and more acceptance of variations in colour, texture and pattern, and acceptance of the occasional knot, will go a long way in reducing wastage. In other words more appreciation is required of the material as a natural product.

Resource efficient design is the practice of designing to maximise the utilisation of a material. As timber, for example, comes in standard lengths in increments of 300mm, it makes sense to rather design a deck say, of 3m wide, than 3.2m; which would result in a 200mm off-cut of each piece of decking. Similarly the practice of placing studs at 400 or 600mm centres is ‘resource efficient’, as this coincides with typical internal partition board widths of 1200mm.

Enhancing Durability

Correct detailing of externally exposed timber serves to enhance durability. Timber and should always when wet shed water, for example by bevelled edges. Moisture traps should be avoided and natural ventilation provided, particularly below suspended floor structures. End grain should not be exposed to weather in such a way that water lingers.

Design a building which will be enduring in terms of aesthetics

Sustainability, as a concept, is all about what we leave behind for future generations. The main aim, above all, in terms of sustainable design, should therefore be to  create buildings with a timeless architectural quality, an enduring aesthetic appeal, adaptable or easily modifiable over time, and beautiful within their environment, so that future generations, rather than wanting to remove and replace them, will to want preserve and live in them.

The current state of the building industry and the trend towards Green

We have been through one of the worst downturns in the construction industry for some time and all indicators point to the fact that recovery is going to be slow. In fact it has been said that the new ‘normal’ once the market has recovered, will be nowhere close to where the old ‘normal’ was.

There is a change occurring though.

As we slowly emerge from the recession, and the number of enquiries I receive certainly is’nt increasing dramatically, it is the change in the nature of the typical enquiry that is more relevant.

In the past if someone enquired wanting to find out about getting a timber house designed, it was more than likely because they simply liked the idea of living in a timber home. Today, I am just as likely to get an enquiry from someone wanting a ‘green’ home, and as a result of that they are considering building a timber home.

So while the market for new construction is still trying to pick itself up, there has been a growing trend in interest in ‘green’ buildings. Consumers have been made aware, thanks largely to the media, (just about every décor magazine has had a special ‘green’ issue) that by making the right choices they can make the world a better place  – and timber homes tick all of the right boxes.

On a brief search online, on websites such as ‘trendhunter’ and others, reveals that the current trend towards eco-homes includes consumer concerns over issues such as:

• energy efficiency
• healthy homes
• harder floors (carpets are on the way out it seems)

 (note timber homes still ticking all the boxes)

…and other issues more related to design and technology such as:

• smaller spaces (and in true American style it’s been given a catchy name; “rightsizing”)
• alternative energy

The downside

 The downside is that every supplier of every type of product and service is claiming to be green. All it takes is for a environment unfriendly product to be made slightly less unfriendly …”eco” cement being a case in point.

Consumers are therefore hard pressed to distinguish between real ‘green’ choices and ‘greenwash’

To counter this, information needs to be accurate and backed by credentials. With so many offerings to choose from, consumers will, as they are doing overseas, start looking towards certification to distinguish between the ‘talkers’ and the ‘do-ers’. For example asking for FSC certified timber and wanting buildings the are rated by the South African Green Building council’s Green Star rating system – although it may still be some time before there is a category for single residential buildings. Expect also in future an increasing demand for eco friendly timber treatment such as tan-e.

How Design is responding to the Green movement

• More designers, becoming aware of the shift towards green building, and are likely to start specifying more sustainable materials such as timber and designing timber homes
• There will be a re-emergence of design strategies such as passive solar design ( re-emergence as most buildings were designed with these strategies before inventions such as heaters and air-conditioning). An example is the amount of books which have recently become available  – the architecture section at a bookshop like Exclusive Books will have a whole shelf of books on ‘Green’ buildings, Eco design and even timber homes ..whereas a year ago there would only have been a handful.
• The tools of design have been enhanced dramatically and there will be an increasing demand for us to conduct energy modelling in the design stages.

 From CAD to BIM

Where we went from drawing boards to CAD in the 90’s, there has been rapidly increasing development in new type of design software called Building Information Modelling.

Whereas CAD is simply drawing on a drawing board enhanced to essentially doing the same thing on a computer, ie still essentially drawing lines and pictures, with BIM one actually constructs a virtual model of your building as you design, using entities such as walls, columns and slabs. As these entities can be given attributes, for example a timber frame wall with fibre cement cladding on 9mm OSB with 100mm Isotherm between the studs and 15mm gypsum board internally, it can also calculate R-values and heat retention and therefore can model overall thermal and environmental performance using add on packages specifically developed for this purpose.

A report released last month by McGraw-Hill Construction, titled “  “Green BIM: How Building Information Modeling is Contributing to Green Design and Construction,” states that the growth of the green building and the development of BIM are currently two of the most dynamic trends in the construction industry.    

 “Green building is already transforming design and construction in the U.S., and BIM has the potential to increase innovation—and design and construction efficiency,”

 “Although they have been growing independently, it was inevitable that they would converge because the analysis and simulation capabilities of modeling are such a natural fit with the objectives of green building.”

Green Design with BIM

BIM can aid green design by:

Analytical sun studies

Conducting a sun study helps the designer to evaluate and refine his project to effectively use daylight sources.

Continuous control of usage of resources

Quantities and detailed data about building components can be generated, providing the architect and the owner with valuable information about the materials used.

What-if scenarios for design optimization

The ability to run different scenarios supports the green design process.

Computer energy simulations

An example is EcoDesigner which is a plug in for ArchiCAD, which is what I am using. As soon as a design takes shape, comparative energy reports can be generated with a click. The resulting reports give feedback about the buildings energy usage, yearly running costs, and carbon footprint.

See http://www.graphisoft.com/products/ecodesigner/

Conclusion

Timber frame is used in buildings around the world. Despite statistics such as 70% of the developed world’s population live in timber frame homes; 90% in Canada and the US, and 20% in the UK, it has a relatively miniscule share of the local market and figures are hard to find. Between my own ‘guestimate’ of half a percent, and the Wood Foundation’s 2%, lets for arguments sake say timber homes make up 1% of the residential market in SA.

Why so many people in SA still choose to build in brick, something that is still done the same as it was a 100 years ago, when everything else around us is changing so rapidly, think cellphones, internet, advances in medicine, and of course the environment and the state of the world, is a mystery. My bet is that, as the pressure on resources increase and the efforts to slow down global warming escalate, and the message from the media to make the right choices gets ever louder, there will be a shift. And possibly a large one.

At our, for arguments sake, 1% of the market, even a 1% shift from brick to timber frame represents a 100% increase in demand for timber homes. A 2% shift represents a 200% increase and so on. I think our industry may soon get very busy.

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