I read an article in The Conversation recently, posing the question “If we stopped emitting greenhouse gases right now, would we stop climate change?” The sobering answer is, unfortunately, no. The principal reason is that CO2 and other greenhouse gases persist in our atmosphere for centuries, all the while trapping in heat and making our climate warmer. This effect is delayed somewhat, because the Earth’s oceans act as a giant thermal mass – which means they can absorb a lot of heat before releasing it into the environment, potentially decades later. The article went on to make the point that given the political and economic difficulties we face in getting off our addiction to fossil fuels, we need to be planning for a world in which temperatures are somewhere between 4 and 6 degrees C warmer than current averages, within the lifetime of our kids and grand-kids. And this is before we take into account wild-card events such as permafrost thawing, whereby vast quantities of methane (an extremely potent greenhouse gas) is released. This is not a depressing possibility – this is our best-case future. This, as they say, is not a drill.
Which brings me to the subject of this blog post. The main reasons people build Passive Houses are comfort, and energy efficiency. There are of course other benefits to Passive House, one of which is durability – PH buildings are designed to last a long time. It strikes me that in a not-too-distant future of higher temperatures and scarce resources, building a PH – especially one designed to cope with hot weather – might just be the best things we could do. Not just for ourselves, but for our descendants.
In terms of sustainability, a multi-generational PH dwelling ticks a lot of boxes. Building a home right – that is to say, building a PH home – will dramatically reduce energy consumption (and therefore carbon emissions) over the lifetime of the building. And because a PH manages humidity and condensation properly, that lifetime can be considerably longer than a non-PH building constructed from the same materials. But what would a PH look like if designed to support the needs of multiple generations – let’s say grand parents, parents and their kids, in an environment where Summertime weather regularly exceeds 50 degrees C?
As we know, the purpose of insulation is to slow down the rate of heat transfer. But after a string of hot days, even the best-insulated buildings can only get warm. And if this string of hot days is accompanied by relatively hot nights with little or no cooling breezes, then our ability to night purge excess heat is diminished, and things can get uncomfortable. Even in bayside Melbourne, it is not uncommon for us to have at least a couple of periods in late summer where this is the case.
As it turns out, humans have been able to adapt to hot climates quite successfully, and I’ve been lucky enough to experience the results in two completely different locales.
Cappadocia, in central Turkey, tends to have long hot summers and cold winters. The region is famous for its marvelously craggy sandstone outcrops, including ‘chimneys’ and ‘fairy castles’. Internet rumour has it this was the area used for filming the Sandpeople scenes in Star Wars. Disappointingly, this is not true, but it’s easy to see why people might think so. For centuries, the locals have created homes and food stores by digging into the sandstone cliffs and fairy castles. I was lucky enough to spend a couple of nights in one such fairy castle on a backpacking trip through Turkey man years ago. It was a wonderful experience, pleasantly cool inside even though the days were hot and the nights freezing cold. And quiet, unbelievably quiet. For me, the perfect place to sleep.
In a similar vein, the residents of Coober Pedy, in South Australia, have also resorted to creating dwellings underground to escape the infernal outback heat and freezing nights. I didn’t get to sleep in a dugout unfortunately, but we did visit one on a tour, and I have to say it was infinitely more comfortable down there than in our tent in the local caravan park…
Whilst there are numerous examples of people living underground to escape the heat, it’s unlikely we’ll see whole underground suburbs any time soon. Moreover, siting an entire house underground might not be a great living experience for the family. But what I’m imagining is the possibility of building a regular PH, but with provision for at least sleeping underground during the Summer. The subsoil temperature at a depth of a couple of meters is usually quite close to the annual average air temperature at the surface. A basement with mechanical ventilation but otherwise outside the PH treated floor area, could make an ideal hot climate sleeping area. By outside the treated area, I mean outside of the area taken into consideration in the PHPP. Hence, the sleeping basement in not technically part of the PH. This is because we are wanting to capitalize on the lower subsoil temperature. Nevertheless, fresh air is important, both from a health perspective, and also to help control the humidity. It would be a good idea for such a basement to have an airtight layer, to avoid ingress of any ground gases such as radon.
Whilst we’re thinking about matters subterranean, I wonder if planning for a warmer future will bring so-called earth tubes back into fashion? “Earth tubes” were a 70’s idea of supplying fresh air to the HRV via an extended length of large-diameter tube buried several meters underground, so that the air is pre-warmed/cooled to the subsoil temperature before entering the house. No doubt such a big excavation adds to the cost of building, and designing the system so that condensation runs to a collection point instead of pooling is also a challenge. Nevertheless, I think the option of using such techniques to pre-cool the air is something to think about.
It surprises me that so few people today realise that the key to keeping internal temperatures down is to prevent the summer Sun from striking the glazing. For north-facing windows (or south-facing in the northern hemisphere), this is easily achieved with horizontal shading such as appropriately-sized eaves, or possibly deciduous trees. East and west-facing glass is harder to shade because the Sun strikes at a low angle. Hence we must consider minimising glazing on these sides, and using external blinds, louvers or shutters. I say ‘people today’ because Australian homes built in warmer climates up until at least the 1940’s tended to have verandas, quite often right around the outside of the house, to prevent the Sun from hitting windows or walls. This was of course, a time before bulk insulation was readily available. Builders just knew that lightweight construction, eaves and verandas worked in the hotter climates.
This brings another old-school idea to mind. Back when I was young and growing up in the back-blocks of Western Victoria, Land Rovers were the vehicle of choice for navigating steep, slippery farm tracks and rough country lanes. I’m talking rough-and-ready 50’s era Series 1’s, not the cushy computer-controlled luxury vehicles driven by the poseurs of Church Street, Brighton. But I digress. Some of these old Landies had a second roof fitted, with a ventilated air-gap between it and the cabin roof. Of course, ‘roof’ on those things meant nothing more than a sheet of aluminium which kept the sun off, and the rain (mostly) out. The purpose of the second roof (which I later learned was known as a ‘Safari’ roof) was to help make the cabin cooler, by keeping the Sun for striking the cabin roof directly. My recollection is that these Safari roofs worked surprisingly well, and I’ve often thought since then that this idea could be adapted for houses in hot climates.
There is no doubt that our comfortable, high-consumption lifestyle is going to change dramatically in the coming decades. Due to committed heating, the global climate is going to get warmer. The challenge before us is to modify our behaviors to minimize the extent of warming, and adapt our approach to housing so we can cope with what comes.
The approach I’ve imagined above – a Passive House, with a ventilated but un-insulated basement and a semi-detached roof structure, is not new. I’ve taken some proven approaches that work well today, and combined it with a couple of ideas from yesteryear. Nevertheless, I believe it’s something we have to think about. Today’s McMansions and block-like constructions with huge windows and no eaves, simply cannot continue. They are a bad idea now, and I suggest in the near future it will not be possible to live in such a dwelling.
What do you think? Are these ideas I’ve presented above a sensible approach to rising temperatures? Or do you think I’m being needlessly apocalyptic, or shamelessly exaggerating the effects of climate change as a way to plug Passive House? Let me know in the comments.