Windows are wonderful features of our houses; they let light and air in and make our houses nicer places to be. It is unfortunate that they tend to be energy black holes, accounting for up to 25% of the heating bill in winter, but this is Australia and they also let lots of heat in during our long hot summers. They cause you draw extra energy to keep the place cool if you have air conditioning or turn your house into a solar oven if you don’t!
The design of our houses can help or hinder our quest to reduce energy consumption but still live with some comfort. I have an enduring grudge against the idiot who designed our house – a huge expanse of glass on the east and west faces of our house but absolutely none on the north wall. Unfortunately many houses are the same, and there are not many of us who can afford to just hack holes in the walls to open up new windows when we feel like it or design their own house. In many cases we have to live with what we are given so I have tried over the years to come up with low cost retrofits to improve the energy performance of our windows without replacing them with low ‘e’ glass or double glazing.
I’d like to share some of our successes and failures with you!
Before we move onto the good stuff though, I would like to put down a few words about blockout shutters, because we have had them fitted to our front windows for over 10 years. There were expensive and a quote to place the same kind of shutters across the back of the house (4 windows) was almost $4000 including a bit of tarting up of the original ones. 
They do block out the sun and reduce internal temperatures; they also do work towards keeping heat in during winter too. Ours are a dark brown and when the sun is on them you can feel heat being transmitted through the shutter and then through the window, but it is definitely an improvement. You can open the shutters up slightly so that holes appear between the shutter slats for ventilation but the amount of ventilation provided is small. The reduction in feeling cold in winter due to the shutters from my experience has been small and I think there are better ways to achieve this. Shutters have their place if you have the money, but my focus was on low cost! So, on with the show!
Bubble wrap
One cheap way to reduce heat going out of, and coming in through your windows is to place a layer of bubble wrap against the inside surface of the window. This traps a layer of still air against the glass and acts like de facto double glazing, but at a much cheaper price. I was all for going ahead with this; it was cheap and appears to work while still letting some light in. Unfortunately, my lovely partner in sustainability declared that windows covered in bubble wrap looked like crap. So that was the end of that! If you are not likely to face veto from The Boss, this is a good, low cost energy saving measure worth trying.
Shade cloth (eg Sarlon)
While this isn’t much good for keeping the heat in during summer it is does provide a bit of respite from the heat. I made up a frame of 19mm x 50mm DAR pine (light, cheap and available) which fit into the brick surround of the outside window frame. I then fitted one or two braces across the frame, depending on the size of the window, to increase strength and give me extra surface to attach the shade cloth to. I then cut 70% shade cloth to size of the frame and secured it using the flat steel shade cloth, for want of a better term, nails. Bingo!
I just fitted it into place and secured it with a couple of wedges. I didn’t do the wedge thing originally and the damn things would fall out when it got windy. They reduce the solar load on the window, but still let you see out and let a cool breeze come through. They don’t have much effect on keeping out the cold in winter.
Gift wrap
Yup, strange as it sounds, the silver metallised plastic gift wrap that you get at the “el cheapo” shops for a dollar or two a roll can be used to reduce the heat load through your windows. Use a frame similar to the one mentioned above, but making sure that the braces are spaced so that they are no wider apart than the width of the roll of gift wrap. If you can get gift wrap that is plain silver on both sides, so much the better but gift wrap that is silvered on one side will do the trick. Apply double sided tape to one side of the frame and then roll the gift wrap shiny side out onto the double sided tape on the frame. Once the frame is covered fit it to the window and secure with wedges.
The gift wrap will reflect solar radiation, reducing the heat load through the windows and keeping the house cooler. It may also reflect heat back into the house during winter. During the day you have a lower light level inside than out, which allows you to still see out through the gift wrap cladding, especially if you were able to get the stuff silvered on both sides. The gift wrap is a bit fragile and can be torn by high wind and also, the reflected heat and light can really crap off your neighbours if it is aimed at them. When setting the reflector up, make sure it is angled up or down so that the neighbours aren’t in the firing line.
Window Quilts
If someone you know is into quilting, get them to make you up some quilts the same size as the inside of your windows. In the same way as a quilt on your bed keeps you warm in winter a window quilt puts an insulating layer between you and the thermal loss or gain through the window. You can make the outside face of the quilt white to reflect light and heat, and put a nice pattern or even a piece of material with a view on it facing inward. Unlike the solutions above, this will not let you still see out and may work a bit better in keeping the heat in during winter than keeping the heat out during summer.
Polystyrene Foam
We get large blocks of polystyrene at work, usually with a thin protective layer of polystyrene foam on the outside of the delivery which is thrown away. We cut the polystyrene to shape with a hot wire cutter so I measured up the interior of our back windows and got the guys at work to cut some of the polystyrene foam to size for me, in two pieces for the larger windows. They fit into the inside of the window and the effect is immediate, the room instantly feels cooler and they also keep the heat in during winter, reducing heating bills. The polystyrene foam I used varies in thickness from 10mm to 25mm and there doesn’t seem to be much difference in performance with thickness although (obviously enough) the thinner the foam the more light is transmitted. You can’t see through it but it will let enough light through to be able to carry on most household activities.
While I cheated by getting hold of large sheets free, you can make the same thing by getting hold of a hot wire cutter (I got one from Hobbyco in Sydney) and slice up waste polystyrene veggie boxes etc into squares and then stick them together edge to edge with double sided tape. The polystyrene is light and easy to take in and out of the window but somewhat fragile so care must be used when taking them in and out of the window area.
Out of all these I really like the polystyrene sheets, perhaps because they work so well. We were going to spend the $4000 and get shutters across the back to try and reduce the solar oven effect (My wife doesn’t put up with the heat well) but since I got hold of the polystyrene sheets we have agreed to put the money towards better things. In reality though, any and all of these are worth trying to see which one works best in your circumstances.
