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Window performance has improved a lot over the last two decades, due mainly to changes in glass coating technology and the emergence of reliable, factory-sealed double and triple pane glazings. Just look at any window advertisement and you'll see what I mean. All this well-lauded advancement creates the impression that the energy efficiency offered by modern windows can't be matched by anything built in a home workshop. Fortunately for people like us, this isn't true. The fact is, high-performance, wood-framed, fixed-pane windows can be built very successfully with a few basic power tools in any workshop. (Openable windows aren't as easy to make well since they rely on specialized hardware that's not easy to find. For assured success, stick to building fixed-pane units.)
If you're like me, you'll find the possibility of energy-efficient, shop-built windows exciting, especially if you're involved in renovating an older home or building an unusual new one. They give you unbeatable flexibility and cost a lot less than ready-to-install versions. The key to success is the availability of custom-made, factory-sealed multi-pane glass units you install into your own wooden frames. Yes, you can buy this kind of high-tech glass in sizes and shapes made to your measurements (even just one or two pieces at a time), from Canadian suppliers listed in the yellow pages or from many building supply outlets. I've just finished making four round windows for the attic of my house and I'm delighted with the quality of the low-e, argon-filled, double-glazed units that made this possible. Here's the scoop on how to build your own high performance windows:
Modern Window Glazings are Key:
Before you get busy making windows, you've got to know a bit about the modern, energy-efficient window panes you'll be ordering. These are made of two (sometimes three) pieces of glass sandwiched together with a space between them. An optional extra measure of energy efficiency is achieved by filling this space with argon gas and by coating the glass with an invisible film (called a low-e coating) that reduces the loss of radiated heat from your home. When the time comes to order you sealed glass units, you'll have to decide on three things: Argon-filled or plain? Low-e coating or not? What overall thickness of glass unit? Argon and low-e do add a bit the the cost, but not much. Price both plain and souped up panes before you order. Also, keep in mind that thicker sealed units (with more space between individual pieces of glass) have better insulating properties than thinner ones, though there is a limit to the thickness that can be accommodated in a window frame. While it's safest to order glass after you've built your frames and measured the required dimensions, you've got to make a decision about the thickness of the sealed unit sandwiches you'll be using before you start making the frames. Custom glass shops offer different thickness options, so call ahead and see what's available. I chose a 5/8 overall thickness for my glass sandwiches. Also note that if you've opted for a low-e coating, your glass should come marked with an inside and outside surface. You've got to orient the glass correctly to get the low-e benefit.
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Building the Frames:
A typical shop-built window frame is shown here, with all the important bits labeled. Nowadays there's no need to struggle with labor-intensive mortise and tenon joinery to hold frame members together. Double or triple #20 biscuits are quick to install and very strong. They work just fine for window frames, especially fixed units that won't be opened and closed.
The drawing also shows a ledge (called a rabbet) cut into the inner edge of the frame to support the sealed glass unit. The rabbet should face towards the inside of the room on your frames. It's best to cut these window rabbets after final frame assembly, using a rabbet bit in a table-mounted router. The resulting round-cornered rabbets can then be squared up with a chisel. The rabbet should be about 3/8 wide, and deep enough to accommodate the thickness of the sealed glass unit, plus an addition 1/2 for rounded wooden glazing strips, as shown.
Knot-free cedar is the ultimate window frame wood in my book, though it's expensive enough to warrant renting an armored car to bring it home from the lumber yard. On the plus side, it's stable, rot resistant and easy to work with. Canadian windows take a lot of abuse from the weather, so you don't want to skimp on wood quality. Are your windows a low-budget project? As long as you vow to keep your wooden window frames properly coated with paint or sealer, I'd opt for knot-free pine (cheaper than clear cedar) before knotty cedar.
I'm a big fan of those thin strips within a window frame that create what's called divided lights. Whether they're installed on the room side of a single piece of glass (just for looks) or actually divide the window pane into numerous pieces, divided lights can be installed more easily than you'd think. The illustration shows how to set strips of hardwood into notches cut on the inside edge of the frame, then how quarter-round glazing strips are added on either side of the strips to create a ledge for the glass to rest on.
Finishing and Installation:
It's best to apply a finish to all surfaces of your window frame before the installation of glass. A slim, continuous bead of silicone caulking laid in the rabbet before setting the glass over top will keep the weather out. The glass can then be secured within the rabbet by adding glazing strips to the inside face of the window. Use nails only (not glue) to hold these strips in place, in case you have to take them off some day to replace the glass. |
