I believe that everyone and every built should be energy-efficient so when we talk about affordable housing what I’m most concerned about is that the first thing that we seem to tick-off the list and compromise on is the actual performance of those affordable houses. I think this is simply unacceptable.

And I know I’m not alone in this thinking in fact with many design professionals friends we keep discussing those topics on a daily basis, so one of the actions I wanted to suggest is to start the discussion where we all throw on the table everything we know that can make building a home more affordable. So I am inviting everyone into the discussion, let’s share what we know that can make houses more affordable.

Smaller homes are certainly going to cost less and by designing these well they don't have to feel smaller.

Think about what’s most expensive part of the build. Let’s not talk about foundation at the moment since it’s heavily depends on site specific ground conditions let’s talk about superstructure everything above foundation for now and I want you to think about external and internal walls, what is the actual difference between external and internal walls. The difference is that external walls are your building envelope, so they need to be also insulated to retain the energy and they need to protect you from the weather so they need to have cladding on. So this means that external wall will be much more expensive to build in terms of material costs then the internal wall will be. When you look at your design, your floor plan, you can look at all the external walls and know that those are gonna cost you more than the internal walls. So by having less external walls you will be able to save cost. And how do you do that, by designing a floor plan that doesn’t have a lot of steps on elevation. If the elevation is more 'faceted' it will have longer walls to go in and out which basically creates cost. Arguably it’s almost more efficient to build this step-in as an internal space because at least you’ll be able to use that corner as part of your living space.

Example 1 less external walls

Example 2 more external walls

The less external walls you have the less walls are actually separating you from the external environment which also means that it is easier to keep the heat in because with a smaller area of your building envelope, smaller area where the heat escapes through.

Now same applies to the roof, Roof is also your building envelope and when the house performs well you will be losing more through the roof then you will through the walls, so it’s really important to have your roof done well. So you could create a 200 m² floor plan on a single story and affectively end up with 200 m² of your roof, or you could create a two story structure and end up with only 100m² square metres of roof which is also a saving because instead of building 200 m² of expensive insulated roof, you are only building 100m² of roof.

Building a two story building will always have additional costs. It is mostly attributed to time it takes to build two stories. Built is happening in stages, first floor, than midfloor, then second floor, if it takes longer it is also more expensive. You need scaffolding to bring up materials to apply cladding etc, it takes more energy to bring materials to second floor, but still.. certainly some savings on the materials.

The next topic is obviously openings; windows. Now you have to know that those prices are changing all the time and don’t hold me accountable for anything I say here but quickly looking things up online it appears that the windows will cost you about $350 per square metre (link) and we are talking double glazed thermally broken aluminium window, you shouldn’t do anything less anyway. Now if we compare these windows with well insulated wall with cladding, we are probably talking approximately $100 per square metre for the SIP wall or a well insulated wall (link) and then we actually had to apply cladding on as well, so we’re probably looking at at least $150 per square metre for a decent cladding. So less windows is going to be cheaper.

But also thinking about the performance of the home. On average R-value of window is probably just about a 1/10 of what a Wall can do. Thermally broken double glazed Argon field window will have R0.4, a well insulated SIP Wall will probably be more like R4. So it’s 10x better..

While the window also brings in the light and in some cases solar gain, the free energy, we need to be conscious of where we put windows and how many, instead of putting a window on every wall.

If you want to learn more about placement of windows and how to design your house for the sun utilising its solar gain but also protecting yourself from overheating, there’s a separate webinar I created on this link. But this question is more about the building science and now we are talking cost here.

Another topic is the design of the windows and I’m asking for some feedback from manufacturers and designers with experience here. I was told that the windows to about 2.1m high are more cost-effective. Also that it makes sense to have a horizontal mullion at about 1m, smaller pieces of glazing, that’s gonna drive the cost of glazing down? Sliding windows are cheaper than bi-fold? But french windows are more air-tight as these better compress the air seal? I’m interested to hear more feedback from from people in the industry, let’s share some knowledge.

Ceiling height is quite important. If you were to use plasterboard for lining your walls it’s worth looking at the correct ceiling height to optimise the usage of plasterboard on your walls. Builders will tell you that certain ceiling heights are much easier for them to install plasterboard because it not only uses less plasterboard in total, but it also requires less cutting of the boards, so it’s less labour intensive for the builders. A good ceiling height to work with is 2420mm. The standard plasterboard is 1200mm wide. You need to install this horizontally in two parts which totals as 2400mm. But you need to leave approx. 10mm gap at the bottom, so its easier to install and also you need to allow 10mm of ceiling lining to run past. So this is where you get to 2420mm. More expensive but still well utilised is 2570mm, (using 1200mm standard and 1350mm wide-line plasterboard) and 2720mm (2x1350mm wide-line)

Plumbing and services. It makes sense to keep all your plumbing close together, so looking at your layout, having kitchen facing a bathroom, to share the wall, so that plumbing services can be shorter, stay closer and therefore require less material and less work.

Please help us with your experience, together I’m sure we can come up with something useful, which will allow us to build cost and energy affordable housing.

Please also share this on social media so that you can invite your friends and family and everyone that you know is now interested in affordable housing.