Saskatchewan's Green Directory Helping Saskatchewan choose a better environment

A good window is surprisingly complex, and needs to fulfil several functions at once. In assessing a window, we use the ratings system set out by the Canadian Standards Association in CSA A-440 (which may be consulted in some large public libraries).

What to look for

Minimise air leakage

Does the window meet or exceed the requirements of CSA-A440 category A2 (maximum air leakage rate of 1.55 m³h^-1m^-1 for opening units; 0.25 for fixed units)?

Minimise water leakage

Does the window meet or exceed the requirements of CSA-A440 category B1 (resists water leakage up to 150Pa pressure differential)?

Maximise resistance to wind load

Does the window meet or exceed the requirements of CSA-A440 category C2 (resists wind load up to 4 kPa)?

Optimise thermal performance

Canadian Standard CSA-A440.2-98 sets out a system for determining an Energy Rating (ER) for a window. We recommend that this be as high as you can afford: for fixed (non-opening) units we suggest an ER of +7 or higher, and for opening units an ER no less than -3. [This represents performance substantially higher than is necessary to meet the code requirements set down for Saskatchewan in CSA-A440.] Windows meeting this criterion are likely to have 3 or more panes of high-transmissivity (low iron) glass, multiple low-e coatings, argon or krypton fill, insulating spacers and non-metal frames. Reputable suppliers should be able to tell you the ER for any of their products, or at least provide you with the following information from which it may be calculated:

• total window U-value, in Wm^-2K^-1
• Solar Heat Gain Coefficient (SHGC) for total window
• Air leakage rate at 75Pa pressure differential, in m³h^-1

Adequate light transmission

Ensure you get enough light through. Again, your supplier should be able to provide a figure for:

• Visual Light Transmittance (VLT) for total window

Avoid end-of-life disposal problems

We recommend that frames should be made from one of the following materials:

• timber from guaranteed sustainably managed sources (e.g. with FSC accreditation)
• fibreglass
• ABS (a type of plastic)

UPVC units are not considered because of disposal issues, and metal windows because of poor performance.

Criteria