The walls are formed literally from 'ramming earth' that is just damp enough to hold together between temporary shutters or formwork. The earth is tamped between shutters with manual or pneumatic rammers. The shutters can be removed immediately after completion of a wall panel.
The true beauty of rammed earth is that the earth itself is the final finish on both the inside and the outside of the building. There is therefore no need for sanding, plastering or painting. This was one of the biggest attractions to us for using it on the Living House. In the past we have completed a number of renovations on our existing house and have had extensive experience with the dust and mess that is created when you work with plasterboard. The opportunity to use rammed earth and therefore eliminate the use of plasterboard in our new house was too good to pass up.
You can see in the image to the below that a standard NZ wall would require the following components:
Auckland is lucky to have a temperate climate in general making energy efficient building design relatively simple. As such it is easy to design a house that is comfortable all year round through the use of reasonable levels of insulation, reduced thermal bridging, summertime shading features, and ventilation.
The building envelope of a house (walls, roof, floor, windows, and doors) is one of the most important elements of the design as it can have a huge impact on the energy performance of the building. Traditionally in New Zealand houses are built from a 90mm timber frame with R2.2 fibreglass insulation placed between the timber studs. The outside of the house is then clad with either weatherboards or brick veneer.
For the Living House we have decided to break this pattern of building and instead revert to a more traditional style of building that has been used for thousands of years. Rammed Earth.
Unfortunately it is not quite as easy as digging up some soil and then using it to build the walls of your house. One difficulty with rammed earth is that strict limits have to be placed on shrinkage to eliminate cracking. A sandy crumbly soil with a clay content around 15% is best. Often cement or hydrated lime is added to improve durability and for shrinkage control. This however isn't always necessary, as many successful structures have been built just from suitable soil without such additives.
We plan on testing the soil that we excavate on our site to see if it can be used to build the walls of our house. Keep an eye on our blog to see what happens!
The good news is that the rammed earth technique is accommodated in the New Zealand Earth Building Standards.
There are many advantages to building with rammed earth. These include superior thermal mass, temperature and noise control, strength and durability, low maintenance, fire proofing, load bearing and pest deterrence, as well as its beauty and the pleasure of building with a natural and environmentally sound material.
The external walls of rammed earth buildings should be a minimum of 300mm thick, providing excellent protection from extremes in climate. The thickness and density of the material means that heat (or cold) penetration of the wall is very slow and the internal temperature of the building remains comparatively stable, with the end result of it feeling warmer in winter and cooler in summer than the outside temperature.
The thickness and density of the walls mean that noise transmission is very much reduced. This is particularly useful if you want to keep out the noise of traffic or in party walls between townhouses. The muting of external noise provides a quieter, more sheltered ambience, particularly evident in bad weather. Rammed earth internal walls are also extremely useful in providing sound insulation between areas with different needs — for instance between living and sleeping areas, or between a public or family room and a study area. CSIRO tests quoted in Bulletin 5 Earth-Wall Construction indicate a sound transmission rating of more than 50 decibels for a rammed earth wall of 250mm. Thicker walls, such as our standard walls of 300mm load bearing walls, provide even better sound insulation.
Strong and Durable
As CSIRO research (and centuries of years of use worldwide) has proved, rammed earth is extremely durable and weather resistant.
Rammed earth walls are extremely low maintenance. Once they are built and sealed, they shouldn’t need any further attention. They are features that stand alone and don’t need finishing with plasterboard or render, inside or outside. There is no need to ever again spend time and money painting.
Earth doesn’t burn. Earth-Wall Construction, Fourth Edition showed that a 250mm earth block wall achieved a 4 hour fire resistance rating. A 150mm earth block wall achieved a rating of 3 hrs 41 minutes.
Rammed earth walls at 300mm thick are load bearing, so you are unlikely to need other structural framing for your home, reducing fire and pest susceptibility. Rammed earth also provides substantial bracing to buildings — usually well in excess of the legal requirements achieved by most timber framed homes.
Termites and other pests simply aren’t interested in rammed earth, and as the walls are load bearing it reduces the amount of termite-tempting structural timber. There are no cavities in rammed earth walls for pests to live in, or to use as a route to the roof or other timbers.
Healthy and Environmentally Friendly
Rammed earth is non-toxic, non-polluting and ‘breathes’. This creates safer, more people-friendly buildings. It is very low in embodied energy, and extremely comfortable to live in.
Benefits of Rammed Earth
2) Nails (to fix weatherboard)
3) Undercoat and top coat (to protect weatherboard)
4) Cavity batten
4a) More nails (to fix cavity batten)
5) Building wrap (or rigid air barrier)
6) Staples (to fix building wrap)
7) Timber Framing
10) Screws to fix plasterboard
11) Plasterboard adhesive
14) Paint topcoat
The downside of rammed earth is it is very labour intensive. Consistent workmanship is critical for both the appearance and the strength of Rammed Earth walls, so site work has to be of high quality.
Image from BRANZ
Image from SIREWALL
Whereas a insulated rammed earth wall can be constructed with just:
3) XPS insulation
Image from greenspec.co.uk