Our intention when designing and building a Terra Firma Rammed Earth Home is to present a home that is as sustainable as is realistically possible in our current construction climate.
What we see as sustainability issues are:
- Cost – even mortgages need to be sustainable
- Healthy – a home needs to breath and have as little toxic materials in it as possible
- Durability – a house must be built to last so that resources can be used responsibly
- Aesthetic – the structure will not be sustainable if it is unattractive and nobody can bear to live in it
- Local materials – our first priority with sourcing materials is to find them locally
- Endangered resource – we need to preserve our native forestry and give them time to grow back to be a sustainable resource for construction. We see locally grown timbers such as macrocarpa and redwood as a very relevant option
- Low maintenance – lifestyles need to be considered here
- Comfort – once again a home must reflect lifestyle expectations
With these general considerations we have developed a specification set that guides our design principles, below is a brief summary of what goes into our homes:
Foundations & Flooring
Enhanced finish concrete floor slab. A concrete floor is cost effective and maintenance free, it also provides very effective thermal mass in conjunction with rammed earth walls. Selections of dyes enable an attractive range of colours and visual textures to be achieved. The floors are finished with Tung Oil, which leaves a permanent durable surface.
Rammed earth walls have ample strength to support mid-span concrete floors for two storey homes. This is particularly advantageous when noise and fire control is required between levels. Although concrete does have high-embodied energy it can last a very long time, which we feel at this stage, is an acceptable offset. Also development progress is being made quickly now with ‘green cement’ which we will incorporate into our methods when commercially available.
Rammed Earth Walls
Rammed earth walls are standard for all exterior walls, interior walls are a mix of rammed earth and timber frame depending on structural requirements. We use up to 10% cement as a binder; once again we see the use of the cement as an acceptable compromise considering the enhanced durability it brings to the earth walls.
The rammed earth walls are a minimum 350 mm thick and are left in their natural state.
Concrete poured insitu over the top of earth walls and openings to connect and tie the walls together to finalise structural integrity.
Typically a truss roof although rammed earth walls are capable of taking a very heavy load including that of a concrete roof (with sod overlay!). Our preference is to use. Where timber is exposed our preference is to use suitably durable timbers (exotic NZ grown) such as Macrocarpa or Lawson’s Cypress, however there can sometimes be resistance to use of these timbers by territorial authorities insisting we use treated wood. We are also comfortable with the use of kiln dried, untreated pine inside a rammed earth structure as the relative humidity never gets high enough to sustain the growth of rot inducing mould, once again the local council may have a different view and force us into using treated timbers
It is usual for us to specify painted (colorsteel) or unpainted zinc-alume as roofing, this is a structurally safe, clean and weather tight system that uses industrial by-products in a reasonably recyclable manner. Structurally, as mentioned previously, virtually any roofing system can be placed over rammed earth walls including structural weathertight concrete with a living sod layer on top.
For exterior windows and doors we almost always specify timber (occasionally we will install steel joinery where tight security is a requirement). Our timber preferences are with Macrocarpa frames, Redwood sashes and hardwood sills – all locally grown. We typically use a highly specified natural plant base varnish supplied by Biopaint.
As the walls are 350 mm thick the timber sills need to sit atop an extended masonry sill, which is either cast concrete or cut granite.
Recycled NZ wool or other insulation to a similar standard of sustainability (including health safety). The fibres in wool insulation are natural protein based which provides health and environmental advantages over any synthetic insulation - they have no carcinogenic fibres or toxic chemicals.
Poplar TG&V (if available) or plywood with Macrocarpa battens with a natural oil finish. Solid plaster or Gib Board with plant-based paint finish.
Rammed earth walls left in their natural state or painted (plat-based paint) Gib Board over timber-framed walls.
Interior Finish Lines
Solid timber skirtings and architraves, usually Macrocarpa with a natural oil finish.
Cabinets – Kitchen
Solid timber (Macrocarpa) cabinets with either stainless steel solid timber, stone or cast concrete bench tops. All timberwork with natural oil finish, concrete bench tops with natural oil finish.
Natural plant based oil finishes typically supplied by BIOPAINTS. Oils are plant based (typically Tung Oil). It is most important for the durability of timber that any oil or paint finish will breathe, plant based oils and paints guarantee this.
Separate shower box or full wet area shower/bathroom with floor waste. Non-slip oiled (Tung Oil) concrete floor.
W.C. Pans & Cisterns
Robust and locally sourced – using locally sourced manufactured fittings is more prudent for long-term maintenance.
Standard size tub with solid timber cabinet.
Meter board and internal fuse board with circuit breakers. Power points. Internal and external light fittings. Telephone and broadband jacks. TV outlets, and earth leakage points.
All wiring EMF considered.
Engineer designed septic drainage system if no sewer point available. 20,000 lire concrete water tank if no town supply water. Power and telephone trenched to house.