We are setting records for hot weather again in Perth this week, so it seems a good time to share this summer's improvements to our shading.
Externally, our home is shaded by vegetation where possible, shade cloth protecting most glass areas, and an ad hoc combination including: foam mats in a window, a shed against a western wall, folded trestle table leaning against another wall and an assortment of things hanging on the clothesline. Internally, we have experimented with many ways to create an insulating layer in our windows, to keep the day's heat out. Most of these I have previously discussed here or here: towels, old painting canvas, mattress, cardboard boxes, cushions, styrofoam cooler boxes... All of these are good, but this year we are onto something I think is easier and potentially more effective: corflute board.
For those unfamiliar, corflute is a 'twin wall polypropylene sheet'. Because it has a ripple between its two surfaces it creates a layer of trapped air - exactly what you want for insulation. However, corflute allows some light through (more than, say, a mattress or cardboard box in the window), meaning the house can be not quite such a cave on hot days - although, as most of our recycled corflute came coloured black on one side, we are not benefitting quite so much from this property.
We now put corflute up inside five windows on hot days, and have installed a 'permanent' summer panel of corflute across half of the over-exposed glass sliding doors to the southwest facing laundry. The loungeroom window panels, being about two-thirds window height, leave a 'clerestory' window space, shaded by the small eaves, which allows a bright naturally-lit room.
Initial Time: There was no set-up time besides sourcing the corflute, which we did within other activities. We did make a kids' art activity out of decorating the panels for the lounge window, as I didn't want to live with the brand names from their previous life, but that was optional and fun.
Initial Cost: Zero. We picked up our first panel of corflute at REmida, the wonderful centre in West Perth that recycles industrial discards for use by schools, community groups, artists and individuals. The rest came via Tyson's dad, a retired engineer, who had a bunch lying around from disused signage picked up on construction sites. If you have to buy them, corflute panels roughly this size cost about $4-$5 each.
Ongoing time or cost commitment: Every day, a few minutes at each end of the day to put the shades up and take them down.
Impact: A southwest facing vertical surface in Perth in summer receives approximately 3kWh of energy per square metre per day. Its best to shade on the outside, so the heat doesn't get in at all, but providing an insulating layer inside windows slows the rate that heat energy gets into the room, and reflects quite a lot of it back through the glass. Once the heat is inside your house, you have to either live with it or remove it. The latter requires electricity, and lots of it.
As I write, well after dark, it is hot and still, the end of our fourth consecutive day over 40°C (104°F). We've equalled the record for days-over-forty (set in 1933) and if it hits 40°C again tomorrow we will have a new record. Perth is a funny place - although we are all wilting, there is also a slightly defiant 'bring it on' mentality. We wouldn't mind one more extreme day if it meant we got to Break A Record.
Here at our house, we are feeling pretty good about how little we have used the aircon in the past four days: so far only for three or four hours total. We've done most of the things I talked about last time we had a record hot week, in addition to all our passive cooling measures. The corflute board has been up each day and is working a treat to keep out much of the 3+kWh we've been receiving. We also replaced our big rear shadecloth at the start of summer (the eight-year-old one finally perished) and the new shade has a higher block-out rating (90%). If it wasn't for the hot nights and lack of overnight breezes to refresh the house we probably wouldn't have needed the aircon at all.