Designed to last: Long live sustainable housing
What would our houses look like if we designed them to last 100 years, or longer? Ande Bunbury, designer of the award-winning Double Century House concept, examines the issues.
This article was first published in Issue 132 (July–September 2015) of Renew magazine.
With many houses in Australia designed for just a 30-year lifespan (alongside some that may only last the length of the builder’s warranty before major repairs are required), a massive amount of embodied energy is being wasted in our housing stock. Surely we should be designing buildings to outlast us.
We do have examples here in Australia of houses that are 100 to 200 years old. Overseas, there are many still-useful houses that are even older. But effective longevity requires more than just lasting the distance— this article looks at some of the issues to consider when designing houses that last.
First up, there is no point designing a house to last if it doesn’t have all the basics right, such as good orientation and aspect, internal thermal mass (where appropriate) and a location with access to transport and connection to community and services. Tweaks can be made later but if the fundamentals aren’t right the house could be an ongoing liability rather than an asset.
Of course, existing homes may not have these fundamentals. It’s even more important to make the most of the housing stock that we have and renovate well, when possible.
Sustainable design in our changing climate also means considering a warmer or more variable future climate. For example, with increasing heatwaves in parts of Australia, what is the role for thermal mass? In ReNew 130 (and a recent series in Sanctuary), Dick Clarke and the late Chris Reardon considered the difficult question of design for climate change in detail. Long-lived designs need to be adaptable to different future climates.
One term bandied around when considering long-lasting design is ‘loose fit’: the idea that spaces should be flexible and adaptable. People’s needs for housing change over time— small children want to be in the same space as their parents so open-plan design works well; teenagers want more separation and privacy; eventually, the house may become home to multi-generations, with parents and adult children (and their partners) living together, or it may house empty nesters. A well-designed house should be able to adapt to these changing needs without needing to go through multiple renovations. Flexibility for all via universal design is one approach to this (see ‘Flexibility for all’ below).
Another thing that changes a lot over time is technology. Who knows what cooking appliances, for example, may be available in 30 years? That built-in microwave and coffee machine may look really good in your new kitchen, but do you really want to have to replace your kitchen joinery when the appliance dies? A loose-fit design with adjustable shelves and panels can adapt to suit the new fridge or have space for as-yet-unknown devices of the future.
The simpler a system is the less there is to break down and the easier it is to repair. When selecting a system for use in a long-lived house, ask yourself whether it could be repaired if the original company goes out of business or they stop making that product or component.
For example, I prefer close-coupled solar hot water units over split systems, as they don’t need a pump to shift the water from the panels into the tank. Another example, perhaps more controversial, is a preference for timber window frames over thermally broken (insulated) aluminium as the hardware to operate them is simpler and can be replaced, and the frames can be repaired and even partially rebuilt if needed.
Many people would probably think of durability first when considering long-lasting design, but I think it’s less important than the categories above.
Very few materials will last 100 years without any maintenance. The materials your house is built from, particularly the external skin, are exposed to the elements and wear and tear.
However, some materials can last a long time as long as protective coatings such as paint are kept in good condition. There are also plenty of materials out there designed for a longer lifespan, often particularly targeted for the marine environment where everything degrades so much faster.
To get an idea of the expected durability of a material, you can look at the warranty period offered. Although a long warranty doesn’t ensure quality, it is the best we have to go on, along with user and Choice-style reviews. There is more that governments could do here, to regulate for longer warranties and end-of-life disposal requirements by manufacturers, making it more attractive to build in quality.
When it comes to housing, in general, the more solidly built a house is the more durable it is—just think of all those European examples. Masonry materials such as stone, brick, concrete and rammed earth can all last extremely long times. However, there are issues with using these materials as a protective skin; in many climates they may need external insulation to get effective thermal performance. [Ed note: see “Mass Effect” for more on this]. In addition, some of them have high embodied energy.
Inert metal cladding materials such as zinc and copper come at a cost premium upfront but can be maintenance-free for 60+ years. Many examples exist such as church roofs in Europe that have lasted over 200 years.
As another example, conventional metal roof sheeting can come with a premium finish such as Colorbond Ultra, with a 25- year warranty in a coastal (fast-wearing) environment. Even cheap lightweight materials such as fibre-cement sheet can last an extremely long time—think of those 1970s fibre-cement beach shacks. Forty years on and the base material is doing fine.
In terms of longevity, timber needs careful consideration. Depending on the species and orientation, exposed external timber surfaces may need replacement after 25 years. Painted weatherboards can last much longer but require regular maintenance. Internal polished timber floorboards can only be sanded back three times before they become too thin, so for longevity use oil finishes that can be touched up without sanding, or provide coverings to areas with most wear.
Embodied energy is a major factor to consider; a primary reason we want long-lived buildings is to reduce the waste of those buildings’ embodied energy. The energy used to make the materials and products in our houses is huge, as is the transportation to get the products to site. The construction industry by some estimates is responsible for 40% of waste to landfill—this includes new materials being thrown away because they are offcuts or imperfect, or they were ordered by mistake.
Anything that requires heating in its production (bricks, lime for concrete, aluminium etc) has higher embodied energy, but this can be weighed up against its lifespan, maintenance requirements and where it is made (hence transportation requirements). [Ed note: Life cycle assessment (LCA), giving total energy impacts over the building’s expected lifetime, provides a way to quantify this, though it is complex. Architects/designers can use rating or LCA tools to enable you to make decisions about the tradeoffs between embodied and operational energy.]
Anything secondhand or diverted from landfill is preferable to new materials (reduce, reuse, recycle). Probably the most important thing we can do to reduce the embodied energy in the construction of our homes is to reuse what was there before.
In the end, longevity is not just about whether the materials last, but rather a combination of appropriate design, durability, maintainability, embodied energy and reusability. To make wise decisions, you need to consider all these factors.
Flexibility for all
We can’t know who the future residents of a home are going to be, or our own future needs. One thing that many designers now consider integral to sustainable housing design is universal design—making sure the home has features that could easily be adapted for disabled or aged residents. This extends the question of accessibility to the private realm, for example with entry paths, rooms and showers designed wider and without steps for ease of wheelchair use, and switches, taps and other fittings placed in reach. The Livable Housing Design Guidelines include 16 guidelines which covers all the things that make a place accessible. Also see the Australian Network for Universal Housing Design.
This article was first published in Issue 132 (July–September 2015) of Renew magazine. Renew 132 has a building materials theme and explores innovative new building materials.
Rain and heat mean different cladding and finishing choices in the sub-tropics, says Stephanie Skyring, an architect based in Brisbane. But a focus on sustainable materials is key, no matter the climate.Read more
This house in Willunga, SA, uses timber cladding for a cottage feel, but adds low-maintenance Colorbond and magnesium oxide board for the hard-to-reach areas.Read more