Windows

The cottage originally had a glass sliding door, four windows each 1.2m², and a small bathroom window.

My first plan was to replace them with new double glazed ones with uPVC frames. For that I was quoted $15,000 (not including the bathroom window). A bit of a shock, and I thought why not try making my own timber windows and door.

In hindsight, even though I think the final result is good, I would be reluctant to make windows from warped recycled timber again. I might consider making them from regular “dressed all round” timber. But even so it is a lot of work.

Glass

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A vanilla double-glazed glass unit is… not that great. It will let through 5 times as much heat as a basic insulated wall (glass U=2.6 vs wall U=0.5). There are a few ways to improve this but the best value is a low-emissivity coating, which roughly halves the heat transfer (approx U=1.3). It is also optimal to have a 16mm gap between the glass panes, and it should be filled with argon gas.

To have this kind of insulated glass unit (IGU) made to order costs about $500 per square metre. If you are willing to be a bit flexible with sizes however, there are a surprising number of IGUs being resold on marketplaces. Usually they have never been installed, like from window manufacturers who have misordered or had orders fall through. They are typically $100 per square meter.

For older units there is a risk that the edge seal can fail. One window maker gave me a tip to extend their life: apply a bead of black silicone along the edge and smooth it flat with a spatula.

To check which glass surface has a low-emissivity coating, use the flame test (look it up). It’s important to install it the right way around.

I found cheap glass units for the 2 opening windows, the 2 panels of the door, and the bathroom. I had the remaining 2 windows (fixed panes) made new, for $510 each.

Hardware

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In Australia, sliding windows are common. But it is hard to make these sealed properly against air leakage. Better are casement (side hinged) or awning (top hinged) styles, as these allow for a simple compression seal.

Outward-opening hinged windows need a winder mechanism so that they can be opened from the inside through a fixed flyscreen. A double glazed glass unit of 1.2m² weighs about 20kg, and a hardwood sash might weigh another 10kg. So we are talking about heavy duty window hardware to operate these windows. Bunnings will not do.

The gold standard seems to be “Truth” hardware from the US; I have noticed that good window manufacturers use them. It does not seem to be easy (or cheap) to get hold of here though. Instead I found a very similar system “Finista” from Lincoln Sentry. It comes to $140 for one awning window set: operator arm, handle, track, 2 brackets, 2 sash catches, and 2 sash keepers. And it can handle loads of 60kg.

The final piece of the puzzle is a good quality weather seal. I like the Schlegel AQ21 seal because it fits securely into a simple saw cut, compresses well, and is durable. I paid $4 per metre.

Timber frame

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Window frames and sashes should ideally be made from timber species of Class 1 durability (40+ years exposed above ground). Mostly this means dense hardwood like Spotted Gum or Merbau, although Cedar is unusual in being a durable softwood. You can of course buy this kind of timber. But old hardwood framing salvaged from demolished houses is dramatically cheaper. This is Blackbutt, which is a Eucalyptus species of durability class 1.

I haven’t done joinery like this before, so I tried to keep it as simple as possible.

• The sash (moving part) is screwed and glued together at the corners with a simple rebated joint. No way I’m going to attempt a mortise and tenon joint!
• The frame is made of an outer part and an inner part to achieve a total depth of 116mm. The inner sides are wider than the outer sides which creates a “stop” for the sash to close against.
• Another timber acts as a bottom stop, and the winder arm goes through it.
• A groove is cut into the 3 stop pieces, as well as the top, for the weather seal.

All together, this design has 13 pieces:

• frame outer top & bottom: 46 x 35
• frame outer sides: 46 x 30
• frame inner top & bottom: 70 x 35
• frame inner sides: 70 x 43
• sash top & bottom: 70 x 43
• sash sides: 55 x 43
• bottom stop: 66 x 41

I used the table saw in my workshop to rip the timbers to these dimensions. Then glue and screw.

Assembly

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The window frame is screwed into the wall frame.

The sash is then attached with hinges. It is a simple matter to fasten the winder operator arm, track with brackets, and the two sash catches. (Once I had figured out the correct positions for them all… there were no instructions.)

The glass is secured with timber beads on both sides (11 x 15 mm, more Blackbutt). I nailed the outside bead first, then placed the IGU, then nailed the inside bead. I used silicone to seal the edges of the glass.

This window is protected by an eave, so I did not bother to install a proper sill flashing. I just sealed the cladding gap with silicone.

Here is one of the fixed windows which was much simpler. I used a wider bead here which is easier to nail.

Door

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Where the old sliding door was, I built a hinged door beside a fixed glass panel.

To seal it, I made jambs of 50 x 20 mm and cut a groove into one side to fit the AQ21 weather seal (see above). Then I screwed them into the door frame as the seal was pushed up against the closed door.