Energy efficiency - dark walls & roof?
Building appearance and building physics can be perturbing. The question of colour in relation to comfort and climate resilience often comes up (in fact we received an email just today - see below). There’s no one-size-fits-all solution (other than smaller and smarter, of course!) and the answer to better housing isn’t to make them all light coloured (light-footed… yes!).
Thistle Hill in Burra, NSW (just outside the ACT) and Blackburn House in Watson.
Hi Lighthouse
I love your designs. I was looking at your recent award winners. I am curious and perturbed as to why you use dark, and black exterior cladding and roofs on energy efficient homes.
Surely the insulation has to work harder. As global warming increases summer maximum temperatures won't the exterior skin temperature be very high? Leading to heat island effects and high skin temperature. This could warp structural elements of the homes.
Do you take account of this?
Kind Regards, X
We’re happy to share our thoughts and experience to help people wrap their heads around some of the many, often confusing, things that make for a comfortable, healthy and durable home suited to your particular site and climate zone. Jenny happened to read this email when she had some spare time this morning (ie she was procrastinating and doing this instead of weeding her garden!) and then she decided to share it more widely (so here it is below and now she will go and do some weeding).
Hi X, I’m sorry we have perturbed you!
The following blog I wrote focuses more on the roof but everything in it is also relevant to walls: Does roof colour really make a difference?
Due to good design and science detailing, and quality construction, the structure of this home will be very durable – the temperature and humidity conditions in the interstitial spaces (the wall and roof cavities and sub floor) will be much less variable than in a typical, poorly-sealed, inappropriately-ventilated and patchily-insulated home (of any colour). We plan for our homes to last.
Thistle Hill has RCAC in the main living area. Last summer the home used a total of between 3.5 and 4kWh per day. It’s lovely over summer and will be absolutely fine during heatwaves. See attached.
Window size and lack of external shading are more important than cladding colour. Assuming, of course, that the building envelope is thoroughly insulated – we specify and check the level of insulation and the quality of the install.
We pay a lot of attention to external shading – the entire deck at Thistle Hill will soon (in 3-4 years) be fully shaded by deciduous vines like at my house. The metal, angled louvre eave at this home (and timber version at mine) prevents any summer sun striking the glass or internal slab, regardless of the vines. The vines provide additional shading to the outdoor area and a lovely transpirational cooling effect. Can see/read about the vines at my place in following blog: The good juice on deciduous vines.
We take a holistic approach – our houses perform extremely well over the cooler months but also during heat waves which will become more common in our region. You can read about how my house (with no RCAC) performed during our last nasty ACT heatwaves here. We have collected similar data from other new Light Houses and we also get feedback from our retrofit projects – this extended 1940s cottage has red brick walls with dark brown roof tiles.
Bushfire safety is also important to us and our homes do well in smoky conditions.
To give you a little more detail about how we factor it in at the design stage; the colour of the cladding material is one of the many variables modelled in the thermal performance software. The software uses 30 years of hourly climate data specific to 69 different climates zones across Aus (Canberra and Burra where Thistle Hill is located, are in climate zone 24) – the software models predicted internal temps and associated energy requirements in 20 minute intervals (the team at CSIRO are very good). If the walls and ceiling are not well insulated then the external colour has a greater impact. Yes, the climate is changing and we will experience more extreme heat in the future (and more extreme events at all times of the year). The climate data is about to be updated. We can already focus in on how houses perform during a week of sustained high temps… but I don’t want to get into nitty gritty here – in short, we at Light House, and lots of people in the thermal modelling, housing and health spaces are talking about climate resilience and the impacts of heat and other extreme events. In just the last month, I have participated in some terrific meetings between medical researchers, housing policy and building physics people – interesting times.
What we do here in the ACT region is not appropriate for all climates of Australia – something I stress all the time.We specialise in designing for this climate and the local housing industry. I’ve lived in other very different Aus climates (WA and Tas) and also in Canada and the Philippines. At Light House we’re very aware of optimising for particular sites and their local conditions.
In summary: I think the relative importance of colour has been overblown. Overall house size, orientation/design, glazing area and lack of external shading and landscaping are things we should be more worried about.
Cheers,
Jenny
PS You may also be thinking of Blackburn House – the renovation in Watson.
This house was previously clad with uninsulated, brown brick. The extended areas have instead been clad with Weathertex (a great, lightweight, locally made, reconstituted timber product).
The lower thermal mass more than offsets the slightly darker colour in terms of external heat retention in summer.
The higher thermal mass, brown roof tiles have also been replaced with dark metal roofing (and a big PV system on the northern side).
We do houses of all sorts of colours. Some have light walls and darker roofs, some are all light and some are a mix. They also feature a mix of materials; frequently clay commons bricks or recycled brick with a lightweight cladding such as timber (often Weathertex) or metal. You can see a little sample below.
Waratah St House in O’Connor and Jenny’s House in Wright.
Finniss House in Narrabundah and Bauhinia House in Griffith