Install your own double glazing

If your house is well insulated but not as warm as you’d expect, you could be losing a lot of heat through your windows – glass and aluminium are both good heat conductors. However, it’s not too hard to self-install double glazing that reduces heat-loss considerably and looks smart too, as you can see from the photo above of the finished result. This method uses wood and acrylic (which are both good insulators) for fixed (non-opening) windows.

You’ll need

• Lengths of 18mm x 18mm pine beading
• Lengths of 18mm quarter-round moulding
• 3-5mm clear acrylic sheeting
• 1.6mm x 30mm nails
• Paint (undercoat and top coat)

Tools required

• Measuring tape
• Saw and mitre box
• Hammer
• Drill
• Sandpaper

Step-by-step guide

Step 1

Measure your windows and buy appropriate lengths of 18mm x 18mm pine beading and 18mm quarter-round moulding. Each costs about $2 per metre. (Lighter-weight mouldings are available and although flimsy and prone to splitting, could be used.) Buy a sheet (1.2m x 2.4m) of clear acrylic. For larger windows 4-5mm thickness is good but for smaller windows 3mm will do. On Trade Me, 4.5mm sheets can be had for $120 but expect to pay double that from regular plastic supply houses. You will also need a fine-toothed tenon-type saw and mitre box. Bunnings have been selling adequate sets for $13.

Step 2

Use the 18mm square beading to form a frame against which the acrylic will be placed. Butt joints in the corners are fine. Aim for a space of up to 40mm between the existing glass and acrylic. Accurately measure required lengths of the 18mm square section beading and cut it at right angles using the appropriate slot in the mitre box. You want to be accurate to a millimetre or less.

Step 3

Carefully lay out the quarter-round on the floor in the way it will go in the window frame. Mark each of the flat faces to indicate which will press against the acrylic and which will be nailed to the window surrounds. Measure the lengths and mark the way the angles will go. Accurate 45° mitre cuts are necessary to get neat results with quarter-round. You can’t use butt joins. Be careful when cutting in the mitre box—it’s easy to make mistakes here by having the wood resting on the wrong face!

Step 4

Paint the cut lengths with undercoat and two layers of top coat. I fix beading with 1.6mm x 30mm nails and predrill the nail holes with a 1mm bit, enlarging the top few millimetres with a 1.5mm bit. This prevents the wood splitting.

Step 5

Clean the existing glass window thoroughly, preferably outside as well as inside. Using a jigsaw, circular saw or fine handsaw (12-25 teeth per inch) cut the acrylic to size. The use of 18mm beading means you have some latitude in the size of the acrylic.

Step 6

Nail the 18mm square beading into place. Punch in the nails and fill, sand and paint the nail holes. Peel the protective paper from the acrylic and using microfibre mittens or similar (you don’t want finger-prints on the inside surface!) lift it into place so it rests against the 18mm square beading.

Step 7

Nail the quarter-round into place against the acrylic and punch in the nail heads, then fill, sand and paint the holes. Stand back and admire your handiwork—you’re done!

Save $430!

We double-glazed two medium-sized windows (155cm x 95cm, 122cm x 70cm) for a total of $170. Professionally installed units (Magicseal) would have cost $600. Total saving: $430.