Eco & Green - Natural building techniques for conventional timber frame homes

Whether you live in a conventional existing home or you are building a new one, there are many things you can do to improve the quality of your environment. Many of the techniques I’ll be mentioning below are aspirational but you can adopt some, or all of these over time to reduce your personal environmental footprint and your exposure to building material toxins.

I’ll start from the ground up.


Subfloor

We need to limit the amount of concrete used but balance this with minimising exposure to toxic chemicals. Conventional suspended timber floors are typically supported on tanalised timber piles set into concrete footings. Tanalised timber is toxic and banned or restricted in several countries. An alternative to this is to fix the timber bearers to cantilevered concrete piles. To reduce the amount of concrete used one can have timber jack studs between the bearer and concrete pile. This was typical in NZ before the availability of H5 treated pine in the late 70’s. To go even further, if one has an adventurous engineer, timber posts can be scribed into a stone footing set into the ground. This was historically done in Japan and other countries to keep timber out of the earth where it rots quickly. Once timber is out of the ground and protected we can remove the main durability considerations and the tanalised treatment requirement. Refer Fig 1 for more details.



Floor

Conventional suspended floors usually consist of manufactured sheet materials on joists with finished flooring atop. The sheet material is usually particle board or plywood. Both these materials ‘off-gas’ formaldehyde and other volatile organic compounds (VOCs). This means they give off harmful chemicals that can be absorbed by our body. These are bad for our health and also for the environment. In addition to this both of these materials are non-durable and need to be tanalised (or alternative toxic preservative treatment) when used in wet areas such as bathrooms and perhaps kitchens. One natural option is to revert back to solid timber tongue and groove strip flooring over joists. To protect such floors from water damage during construction and to form a building platform, first frame and clad the roof and external walls and then lay the floor inside. This was the traditional approach in NZ and one can use a natural oil finish. Note that polyurethane, which is usually used, is toxic and also ‘off-gases’ VOCs. Natural insulation can be installed between the joists below.


Framing, bracing and linings

In terms of framing if one is to follow a conservative approach there are alternatives to treated pine. Untreated heart cypress can be used for the structural framing of a typical home and if your house conforms to the low-risk design requirement of the New Zealand building code, untreated douglas fir (oregon) can be used for all enclosed timber framing instead. In this case you will be wanting to use heart grade douglas fir as the sapwood of all species is non-durable.

Douglas fir is arguably the preferred framing used in other western countries as it is more durable and and possibly stronger than the pine used here. We use pine in this country because it is fast growing in our climate and we can harvest the crop four times a century. Douglas fir is also grown in NZ and is readily available at a similar price.

If you want to increase the insulation value of your external walls, 140mm thick framing can be used instead of the more usual 90mm.

Timber frame walls need to be braced to resist horizontal wind and earthquake loads. The studs will carry the gravity loads but without bracing they will buckle under normal conditions. Nowadays bracing is typically achieved with plasterboard sheet linings and tightly spaced fixings. Alternative and traditional bracing techniques include; diagonal timber boards ‘let-in’ to the studs, diagonal metal straps or angles or a ‘lath’ of diagonal timber strips if you have an adventurous engineer.

If one of these traditional approaches is used, the walls can be sarked in timber or finished with an earthen plaster over a timber, reed or expanded metal lath or even over old carpet if on a budget. If a thick earthen plaster is used this will aid in the temperature and humidity regulation of your home. You will want natural insulation in the cavity. Refer Fig 2 for more details.

Alternatively if plasterboard is to be used (or another sheet lining material) the walls can be given a natural plaster or even a natural paint atop. A readily available natural paint that can be used on plasterboard is linseed oil paint. Alternatively if the wall is plastered, a mineral silicate paint may be used or perhaps a clay (alis), milk (casein) or a lime paint could be made up with the desired colour pigment. Note that conventional paint is toxic and ‘off-gasses’ VOCs. You will want to use splash backs in areas subject to water splash for durability.


Claddings and joinery

Externally, the walls could be clad in local, plantation grown, untreated heart cypress weatherboards (refer Fig 1) or shingles over battens. The cladding could be oil finished or painted with a natural linseed oil paint. You will want to use a non fire retardant wall underlay if you want to avoid the fire retardant toxins used in most synthetic underlays. You can also use heart cypress cavity battens to avoid toxic LOSP or tanalised timber variants.

In terms of external joinery (windows and doors) the environmentally friendly option is double glazed untreated timber. This has much less embodied energy (the sum of the energy required to mine, manufacture and transport it) than aluminium or steel and it also performs a lot better thermally. It can have an oil or a natural paint finish.


Roofing

Arguably the most important feature of your home and the one that usually defines a shelter is the roof.

It is hard to beat the cost, durability and convenience of a long run metal roof and for this reason corrugated iron became the kiwi vernacular. However, metal is very high in embodied energy and there are other options. More natural materials include timber shingles, reed thatch, terracotta tiles, green roofs and slate. But unless you can afford the high cost of the natural alternatives which either need to be replaced more frequently or are durable but more expensive upfront, this is one area where you may want to stick with the standard.

Timber shingles are beautiful but in our climate they are non durable unless tanalised. This increases toxicity and renders them unfit for harvesting drinking water. Water reed thatching is the predominate thatching material used in Europe. It is a premium roofing material that also insulates but it is also non durable in our climate. Raupō or bullrush is our local reed and was used for thatching by the Māori and the pioneer settlers. Terracotta tiles are a very durable roofing option, they are heavy however and do not perform as well in earthquakes and the firing process means they have high embodied energy. They are non toxic but pipe penetrations and flashings need to be of lead (coated in an acrylic paint) which must be considered if rainwater harvesting is to occur. Green roofs have enormous aesthetic appeal but they are incredibly heavy (similar to adding a full second storey to a building) which is not very appropriate in earthquake prone areas. They also require waterproof membranes beneath the soil. Finally there is slate, a natural stone and the mother of all roofs if one can afford it!

Once again you can use non fire retardant roof underlay if you want to reduce your exposure to toxins.


Natural insulation

Options include 100% genuine sheep wool (blown in), rigid wool / polyester blends, boric treated cellulose (subject to availability), rock mineral ‘wool’ or vermiculite. If the insulation is to be retrofitted into existing walls, a gap to the cladding must be maintained. Claddings leak and a ventilation gap is required to help them dry out. Also the insulation value of a material is usually reduced if it gets wet. A ventilation gap can be created with a proprietary drainage matt.

If you want more density in an internal wall for sound insulation, a 90x45mm stud wall can be filled with light earth. This can be fitted ‘insitu’ (in place) for a new build or installed as pre made bricks (stuck together with an earth mortar) in a retrofit. This technique is not the best for a conventional 4x2 frame external wall however. It is less insulating than other materials and you would want to use it 300mm thick to achieve good internal comfort levels.


Shower

Walk in showers have become the norm in this country but there is no natural way to waterproof them. Behind and below the tiles is a waterproof membrane. A metal or ceramic shower tray could be used instead but you still have to deal with the walls.

Tadelakt is one option used to waterproof wet areas in the middle east. This was traditionally applied over stable adobe walls and not movable stick frames though. To put this in a conventional home one would have to deal with timber movement to avoid cracks and water damage.

One non toxic solution for a shower is to use a clawfoot bath with a beautiful copper fame for the full surrounding curtain and shower rose, though this option is difficult for elderly or disabled people.


Kitchen

MDF is ubiquitous in the modern kitchen. It is used as a backing for laminated drawers or cupboard carcases or as a substrate for laminated, lacquered or veneered facing panels. MDF is toxic and ‘off-gases’ VOCs. An expensive substitute would be solid timber carcases and facing panels or a cheaper option would be open timber shelves. These can look nice and if objects are regularly used dust will not be a problem. In terms of bench tops, natural stone is the ideal surface. It will last a lifetime and can accept hot objects. Alternatively, oiled solid timber (new or reclaimed) is a more budget friendly natural solution but requires more care during use.


Hot water and heating

Hot water accounts for approximately 30% of a home’s energy consumption and it is hard to beat solar hot water systems in this sunny land. They will meet 50-75% of your hot water needs for free (after the initial outlay) and will have an electric, gas or wetback booster for cloudy days.

For hot water backup, space heating and even cooking, a wood burning stove is a good option in our temperate forested islands. They can be connected to the hot water cylinder with a wet-back and to radiator wall panels in a central heating system. You will need to check with your local Council to see what they allow.

I hope this information has been useful. Much of it is not commonly known and if more widely adopted, over time, environmental toxins and our carbon footprint would be reduced, comfort levels in our homes increased and personal satisfaction and quality of life enhanced.