Harmony House





We paid attention to our building material choices in order to enhance the success of our passive solar house design. Along the way we made some great finds such as thermally conductive wooden floorboards, and self-cleaning low-maintainance cladding. We also discovered the joy of rammed earth! Read further through this page for more information on our aims, research, decisions and results, as well as our tips and advice summary, for this element of our project - building materials choice.


Our aim was to use building materials that would implement, or even enhance, the success of the passive solar house design we had chosen (see House for more details on the design itself). Aesthetics were also an important consideration in materials choices.


In essence, the Design For Place house design is a cladded stud-frame house, with particular attention given to building orientation, window size and placement, internal thermal mass and insulation. As the building orientation, window schedule and insulation ratings were all clearly defined within the design, our focus for building material choices tended to be around the internal thermal mass options and cladding options open to us. Both those areas - internal thermal mass and cladding - have a major impact on the look and feel of the finished dwelling as well as being crucial to passive solar design success.


The three building materials decisions that most impacted the finished success and looks of our house were: the living room walls, the floor, and the cladding.

The living room walls are an important design element of the house, in that they comprise a significant amount of  internal thermal mass. Internal thermal mass plays an important role in stabilising internal temperatures, basically by soaking up heat during the day and releasing it slowly overnight (for a more in-depth explanation see the thermal mass page on the YourHome website).

The Design For Place design calls for masonary living room walls. Although they can be simple brick, I became  taken with the idea of rammed earth for two main reasons. Firstly, the thermal properties of rammed earth, in regard to how much heat energy can be absorbed and how long it takes to absorb and release that energy, happen to be better than brick and ideal for the day/night timeframes involved in a passive solar scenario. Secondly, rammed earth simply looks fantastic.

Certain properties of rammed earth, such as specific heat capacity, make it a superior choice for passive solar house designs

We found a very well-priced and professional option in Dave Lovell of Earth Structures Peninsula so made room in our budget for rammed earth living room walls to take advantage of the superior thermal properties and superior aesthetics that rammed earth offers.

The next most important internal thermal mass feature is the concrete slab itself, which in many passive solar house designs (including the Design For Place design) is polished on top to become the lived-on concrete floor. We had taken the extra step of insulating our concrete slab to increase the energy efficiency of our house, but we weren’t overly keen to use the slab itself as our flooring: the aesthetics of polished concrete doesn’t appeal to us (too cold and industrial-looking for our tastes), and likewise the feel of polished concrete underfoot isn’t something we’re keen on either. However, covering up the concrete slab with carpet or floorboards would negate its effect as internal thermal mass (as the carpet or floorboards essentially cut off the slab from being able to soak up sunlight and re-radiate heat energy effectively).

Concrete slab with side insulation for better thermal performance

This is a quandary that faces many passive solar home owners: the wish to use the slab’s mass to help regulate internal temperatures, competing against what many consider an unappealing flooring option (polished concrete). After some heartache and soul-searching, we mentally conceded to the necessity of ‘living on concrete’ in order for our house to perform as desired… But we were saved at the last minute by a flooring option relatively new to the market that I hadn’t come across before!

That flooring option is HeatWood by ECO Timber Group. It’s a product that’s been designed for the hydronic heated floor market (as they also need heat transfer between the slab and the room) and which works perfectly in a passive solar house scenario as well. Made mostly from composite stone (14mm thick) with a thin layer of wood on top, the product is designed to give excellent heat conductivity without any destabilisation of the timber.

HeatWood floorboards by EcoTimber Group are designed for heat exchange with the slab

I was over the moon when I discovered this HeatWood product, as suddenly we could have our cake and eat it too: we could be thermally connected to our concrete slab, but with the full look and feel of timber flooring!

Likewise the cladding choice was instrumental to the final look and feel of our home. We made another lucky discovery to find something that ticked all the boxes: thermally efficient, low embodied energy compared to many other cladding options, looks great, and as a big added bonus one of the most maintenance-free options available (which positively impacts the full life-cycle analysis of a house as well as cutting down on on-going maintenance costs for the home owner in practical terms).

That cladding choice was the Territory range of fibre cement boards by Cemintel. The look of the different finishes are great, with the ones appealing to us most being the wood-look finishes. We found ourselves once again being able to beat a common quandary: we could now have a surprisingly authentic wood-look for our cladding, with literally none of the on-going maintenance or wear issues that wood cladding comes with. In fact, Territory panels go a big step further with the use of what they call ‘NichiGuard’: a self-cleaning coating where silica particles in the finish absorb water molecules from the air and form a protective film on the surface, so that dirt doesn't attach directly to the panel, but washes away when it rains.

Territory cladding from Cemintel requires no oiling or painting, and has a self-cleaning coating

So rather than any on-going time consuming and expensive oiling or painting regimes that many other cladding options (particularly wood ones) come with, the Territory boards at most need a wash down with a hose once a year to get any sections the rain doesn't reach. That, together with the durability and long life-cycle of fibre-cement as a material in itself, and it’s great R-value for a cladding, made this cladding choice a very good one for what we were trying to achieve.


In the build schedule the rammed earth walls came very early (the first thing to be done after the slab itself), with the cladding installed during the later half of the build, and the flooring going down near the final fit-out stage.

The installation of the rammed earth walls was a joy to watch. An appropriate earth mix is loaded into formwork, then pounded by a hand-held rammer until it ‘rings’ (having pretty much turned to stone).

Rammed earth formwork

Depending on the size of a job, from single walls to full houses, rammed earth installations are often done in teams of two or more people. For our job, Dave Lovell was quite literally a one-man army, with seemingly endless energy and a depth of professionalism to go with it. Within just a couple of days we had magnificent-looking rammed earth walls reaching up from our slab. They were quite a sight to behold, made even more impressive with the knowledge that there are examples of rammed earth structures around the world that are thousands of years old - if anything about our house was going to stand the test of time it was going to be these living room walls!

Rammed earth has been known to last for thousands of years

When it came time for the cladding, it was important for our builders to read the instruction manual to become familiar with the installation procedure for the product. Cemintel notes that there will be a small learning curve on the first day or two, which is usually made up for with what they say is essentially a fairly easy-to-install product.

The logistics of organising the HeatWood flooring installation during the fit-out needed thought in terms of which bits of the fit-out were best done before the flooring and which bits after. When the ECO Timber Group team arrived to do the installation, they did so with a very gratifying amount of attention-to-detail and professional pickiness that I found confidence inspiring (there’s nothing like a tradesman that will do as good a job for you as they would for themselves).


With regard to aesthetics, it’s often hard to know from small samples of things like flooring, cladding and rammed earth how things will actually end up looking en masse, so we were quite relieved to see that our choices really did blend well together, achieving the naturalistic palette of tones and textures that we were after.

With regards to performance of those three elements (i.e. the internal thermal mass of the connected floor boards and slab combination; the internal thermal mass of the rammed earth living room walls; and the R-value of the cladding) it would only be by moving in that we’d find out if they did their job in the expected temperature stability of the house.


The house design works marvellously, keeping internal temperatures generally in a very comfortable 18-26 degree range year round (see House - 'Our Experience So Far’ - for more detail), meaning the design elements are working as intended. It’s great to know that our careful choices have had such a positive impact on the energy efficiency of our house.

And the aesthetics must be working too: we get many positive comments about the look of the cladding and our floors, and particularly the beautiful rammed earth living room walls, which add such a naturalistic and attractive signature look to our main living area.

Rammed earth has superior thermal properties and fantastic aesthetics


     - Understanding how passive solar design works can help greatly in materials choice (and once again, the information on passive solar design and materials found on the YourHome site is as impressive as it is readable).

     - I found spreadsheets an invaluable tool to compare side-by-side different aspects (R-values, heat capacities, prices, etc etc) of various choices.

     - We are very happy with our inclusion of rammed earth, the thermally conductive wooden floorboards, and self-cleaning low-maintainance cladding. These material choices have enhanced the effectiveness of our passive solar house design.