While this question might sound a little comical to some, it is a genuinely understandable
question. Ramming the earth sets off a reaction within the soil that basically changes it into
sedimentary rock – a mechanical reaction that we can call ‘man-made’.
These walls harden quickly when rammed, so the walls stand up to all elements as soon as
the wooden forms are taken off. They also continue to get stronger over years, just as
natural sedimentary rock does.
Regardless, there will be times that we know the home may be exposed to horizontal rain.
In these cases, we will add an inexpensive, invisible and eco-friendly preparation to the
required walls that takes effect as said walls go through their natural drying process.
Over the last 30 years, we have worked with probably twenty different territorial authorities
and all of our homes have received building consents. That said, because we work with what
is considered today as unconventional building materials, we are extremely thorough with
our paperwork and compliance.
Ironically, rammed earth construction has been around for thousands of years – well before
fired brick and stick framed houses were even conceived. We can report that, once building
inspectors have been introduced to this medium they are incredibly encouraging and love
the quality of our work. In fact, it’s not uncommon for building inspectors to arrive outside
of their work hours and want to learn more about the process and generally catch up with
the crew, as a matter of personal interest.
There are places in the world where rammed earth walls are built with insulation inside, namely alpine areas or regions where there is very little sun in the winter months and considerable snow fall for months at a time. Wall insulation in those cases is warranted because the building just can’t rely on the sun to warm it as it could in a countries like New Zealand and Australia where insulation is not usually used in rammed earth walls.
What you should know however, is we put chemical-free 100% wool insulation into our ceilings and clients report a dramatic reduction in heating costs due to this measure when coupled with rammed earth walls thermal mass behaviour that naturally conserves heat from the sun. To understand this, consider the sun warming up the rammed earth walls through the day, releasing radiant heat in the home during the evening and the insulation in the ceiling stopping that warmth escaping.
Note: we’re keen to test hemp insulation and other suitable natural fibers, as soon as it becomes available in NZ.
Rammed earth walls are what we call high density walls. They are between 350mm
and 400mm thick in most cases. Put simply, walls operating on thermal mass principles regulate indoor/outdoor temperatures because of the way they store ‘heat and cool.’
If it’s cold outside, the walls release stored heat to the inside environment to regulate it. If it’s hot outside, the cool walls release their stored ‘coolness’ into the indoor environment. More on the science of thermal mass can be
This is a difficult question for builders and in some cases a little like asking how long a piece
of string is. However, prospective clients need a guide so we usually estimate it will cost
$3500 per square metre. This figure includes a fully finished house with bathrooms and
We cover all these details at the free initial 1 hour consultation and welcome any questions you have. Costs will naturally rise as a more modest home design becomes complex. This might include unique design features, challenging site access or remote locations. We do also stress that when a client is using their own architect for design, this can inflate costs due to that designer not having grasped rammed earth engineering necessities. For that reason, we always ask to be part of the design process when an architect is leading it.
When building any new home, be prepared to meet the following costs, in addition to the design and build fee: extensive earthworks to prepare the site for the dwelling, water storage, waste water systems, off grid power supply and landscaping.
The building cost estimate is also separate to the design fee. This is a logical separation of jobs, just as it would be in the case of an architect designing a home and a building company building it. We’re pleased to be able to offer both services and stand by our rigorous training and designs wholeheartedly. Have a look at a selection of our design and build homes on our Portfolio page.
When it comes to design, we enter into a pre-contract Research and Logistics Agreement with clients that allows us to design a home and thoroughly explore all potential costs to design and build. Naturally, we cannot accurately assess the cost of a build until we have a design finalised
Absolutely! Hanging pictures on these sturdy walls is easy to do. Simply use a 5mm masonry drill bit, drilling down on an angle and inserting in a 3- 4 cm piece of No.8 wire.
If you later change your mind, the hole is easily and quickly filled with a mix of moistened soil and sand. Feel free to talk to us about this for advice or as an add-on service.
Rammed earth walls prove to need very little maintenance over a long period of time. There is no paint required and the dense walls stand up to the elements incredibly well.
It is also easy to repair them if they get damaged by kids playing indoors or, in one case, a tractor driving into a wall!
Conversely, timber joinery and other exterior timber work, such as weatherboard and fascia, needs protection from the elements.
We achieve this protection with plant-based stains and paints that are specified for this job. The maintenance required of these stains and paints will depend a lot on their exposure. We’ve consistently chosen The Natural Paint Co. to supply us with these products.
Any walls that will be exposed to exceptionally harsh weather will most likely be sprayed with an inexpensive preparation that repels water. This preparation stops any moisture getting in while the walls dry out. It takes about 3 years for the construction moisture to fully dry out of rammed earth walls that are 350mm thick.
Yes. In many cases, we’ve had owners, family and friends get involved in the building of their own home. This practice aligns with our ethos of self-determination, community and sharing knowledge. Rammed earth building, by nature, allows for significant unskilled labour on site which means it is an ideal opportunity for people to truly get their hands dirty and feel physically and emotionally invested in their home. We assess the likelihood on a case bay case basis, taking into account Health and Safety on site.
Not that often. It is, in fact, quite rare that we can use soil from a site. To build optimally with rammed earth, the soil mix has to be very specific to start with. We assess all earth sources for particle size distribution (clay, and and silt profiles) to ensure the considerable strength that rammed earth walls promise.
In our experience this means older soils and we have several sources readily available in different locations to keep logistical carbon footprint light. In other words, we will use a source as close to the site as possible.
An average sized home uses between five and eight truckloads of soil, each load carrying 8 tonnes. However, we can test soil from any site if it has a known high level of sand in it, coupled with a low clay content. These soils are referred to as friable – they crumble easily and lie just below the topsoil.
Yes. The earth for your walls can be coloured but bear in mind, this will add some cost to the project and in rare cases has proved to pose an aesthetic risk. We prefer to work with your local soil’s natural colour and adjust it by adding, for instance, a white cement or lime to lighten it. Even without any interference, natural striations (of colour and tone) will form in the walls during the ramming process and it’s always a treat to see the new wall as all the formwork is taken off. We can easily add stones and shells as part of the ramming process, offering as a touch of individuality and artfulness for those who want it.
While we recommend wooden joinery due to its durability, high R-value, and the sustainability aspect, we can use aluminium joinery and have done on occasion for clients as a cost-saving measure.
No. This is a common misconception and we’ve actually built right in the middle of townships several times. Because of the 350mm thick walls, we explain to clients that a rammed earth house will take up about 8% more of the plot than a timber or brick house with the same internal dimensions.