Thursday, March 17, 2011

The coolest dunny in the west

Our dunny (that's a toilet for non-aussies) is right on the north west corner of our house and the outside western wall has no summer shading. This means that on sunny days it heats up a lot in the afternoon as the sun angle drops and hits it.  In Perth this is a big deal as we have 8 hours of sunshine a day on average over the year and temperatures can hit 35C on a regular basis between December and March. This makes going to the dunny very uncomfortable (unless you want a sauna) and the heat radiates through the back of the house.Our house was built in the 50's using single brick veneer, which is basically a single brick on the outside, with a small air pocket in between gyprock/plasterboard on the inside. Not only does this mean there's no insulation, it is actually the exact opposite of what you want (thermal mass inside to retain winter warmth and summer cool). As an architect said to us, "Oh no, you've got brick veneerial disease!".

So there are variuos ways of combating this disease: you can plant deciduous trees/vines to the west or east to block the summer sun: rip off the gyprock and insulate and replace the gyprock; inject insulating foam through the bricks or deflect the sun by cladding on the outside. We decided to use the last option, we have planted apple trees to the west but they'll take a while to grow enough to do the job. After suffering through the hottest month on record in February (25 days straight over 30C and 15 nights straight above 20C) without aircon we finally got around to doing the job. We got a few tips from our friend Tim and another kind friend helped us out (thanks Alex + nibbler). Here is a pic of the wall with a few pine battons up:

The area is only about 2.5m by 2m. The plan was to put battons up against the wall attached with dynabolts. Next we tacked aircell insulation (like bubble wrap with reflective coating) to the battons:

Then we attached more battons right on top of the first lot of battons. Lastly we attached zincalume metal sheeting onto the outer battons:

We got the tin second hand for free, so the whole project cost about $200. The key to this is that there is an air pocket in between the metal and the aircell and then the aircell and the wall. Lots of heat will get deflected by the metal, but some gets through. Some of that heat will rise up the air pocket and escape and some will be absorbed by the aircell. Most of the remaining heat that gets through this layer should then rise and escape in the last air pocket. The theory is that by the time it gets through to the wall there will be virtually no heat getting to the brick. I borrowed an infrared thermometer from the library and did a few before and after readings. Before the cladding project the outside of the wall would get up to 57C on days around 33-35C, the inside would get to between 35 and 43C on these days. After the cladding the inside wall doesn't get above about 28C on days of 35C, so i reckon that it has made that wall about 10 degrees cooler. In winter the sun sets further to the north and has much less power in it so we don't actually lose any thermal gain at that time of year (thermal gain is highest in the east and west in summer and in the north in winter or south if you live in the northern hemisphere). So here's to a cool dunny!

Slowly but surely we are getting on top of our house's thermal issues. One of the reasons I am so anti aircon (apart from the obvious waste of energy) is that it is just too easy to flick a switch and not bother to fix these kind of thermal leaks. An analogy I like is if you get really bad toothache do you go the dentist or do you just take really strong pain killers and forget about it. Most people would agree that trying to fix the cause of the problem is the way to go. So aircon is like a pain killer, it's ok for a temporary solution but don't forget to go to the cause of the problem and fix it (or better still bare the heat and fix the leaks). Here are a few other ways we've improved our heating/cooling issues. External shading over Quincey's east facing window for summer heat protection. When sun rays hit windows the heat waves actually become more intense, so you really need to stop them before they get to your glass. We remove this shade in autumn.

Another thing we have done in Quin's room is to install a pelmet. We got 5 beauties someone had chucked out onto the verge and at some stage we'll get them all up. By far the best way to insulate your windows inside is by using good quality double lined curtains and pelmets.A pelmet is a box type structure fixed to the wall above curtains. They stop heat loss in winter and heat gain in summer. In summer, air between the curtain and the window heats up. This warm air rises and escapes over the top of the curtain. This air movement sucks cool air in from the rest of the room to window. This cool air warms, rises, and so it goes on in a convective process. In winter the air by the window cools, sinks and draws warm air to the window in the same way and the process works in reverse. Pelmets can prevent 25% of heat loss from or gain into a room (source: protection.pdf).

Over our north facing back door we have a solar pergola which our very clever friend Ryan built (thanks mate). A solar pergola has angled fins which allow sunlight in in winter for solar gain but block it in summer for cooling. The angle and dimensions of the fins are critical so that you get the right amount of sun through when you want it. Ours lets winter sun hit our windows and warms the thermal mass of our cement and tile pad. From mid October the sun is totally blocked out until mid March.

Lastly we have a grape vine to the north which also blocks summer sun and stops heat radiating off our paving into our house. It drops its' leaves in autumn to allow the sunlight through. It also gives us some yummy seedless grapes in summer. It did a pretty good job in its' first summer, next year we're hoping for full leaf coverage and an even better result.

Most of this stuff is based on solar passive design and permaculture principles, so if you want to learn more just do a search or go to the local library. Future projects for us include more pelmets, plastic shrink wrap double glazing, under floor insulation and lots more cladding. Just remember, roof insulation is great but if you don't stop heat coming into your house from walls and/or windows you can make your house into an oven. So after spending many hours in our dunny oven I can tell you right now, it stinks!


  1. Inspirational! I never knew that about pelmets (actually I don't think I understand it that well even now, I struggle with things scientific - but I do get that it's good!)

  2. I like what you guys got going on here. I thought I just made up the term sustainaburbia until I found YOU! lol. keep on rockin it.

  3. I like that cladding idea. And we need pelmets...
    Actually, you have quite a few great ideas.


  4. Pelmets Vs Roller Blinds... we chose modern heat reflective chain drive blinds that fit tightly within the internal frame.. I considered that convection via the tiny gaps would be less than around a curtain x encroaching into the room.
    Clearly, the absolute best suggestion is stop the heat from the outside, rather than containing it inside..

    Thanks for sharing the good ideas - causes us all to think what we can / should do ourselves.