Getting the most out of windows, Part I

It wasn’t that long ago that buying windows was a relatively simple process: Step 1 – choose your frame type (wood, aluminum, or vinyl); Step 2 – choose glazing (single, double or triple); and Step 3 – choose your manufacturer. Providing you had similar frames and glazing, you felt confident comparing manufacturers.

If you were a contractor, you had your preferences based on personal experience, but there was a lot of “opinion” involved in choosing products. I frequently heard things like: “I don’t like xxx (you fill in the name) windows because they leak;” or “I don’t like wood windows because they rot;” or “I don’t like vinyl windows because they warp;” or “I don’t like aluminum windows because they are prone to condensation;” or “I don’t like triple glazed windows because they are too heavy,” etc.

Worst of all, it was hard to compare products let alone manufacturers. Just because choosing a window was simple didn’t mean the process wasn’t flawed.

The fact that so much of the comparison was based on opinion and experience meant that there wasn’t really an objective way of evaluating products and improving performance. Regulators and manufacturers knew they had a problem. To move the technology ahead, they needed window standards that measured performance versus specifying physical characteristics.

If the measurements captured thermal performance, energy performance, wind resistance, condensation resistance and air leakage control, it might finally be possible to compare window types, manufacturers and innovative technology fairly and objectively.

That was the idea behind the development of the CAN/CSA A440 window standard. Envisaged as an “omnibus” standard for all window types, it was designed to measure performance in the key areas in which windows had historically had problems and set targets for manufacturers to meet. With a clear roadmap covering how products would be compared, manufacturers set out to build better windows.

Then an interesting thing happened. Window frame designs evolved from a singular frame type (such as wood or vinyl) to become hybrid materials (e.g., metal clad wood, or steel reinforced vinyl, or thermally broken aluminium, and even fiberglass windows). Testing revealed the importance of these options in terms of performance. New options also crept in for things like glass coatings, thin intermediate films, Argon and even Krypton filling between the glazing layers, and better spacers separating the glass/films.

Suddenly, consumers, builders and renovators had more and better choices for windows.

So from this short description of history you can probably guess I am pretty impressed with the system Canadians came up with for rating windows. And if you have looked into buying windows recently, you probably have noticed other ratings on windows coming from some manufacturers. You may even encounter products manufactured by American companies, or products manufactured by Canadian companies for both the American and Canadian markets. What’s going on?

Well let me start by saying that building physics don’t change just because you cross the border, but it does make sense to manufacture windows close to where they are being used, be that north or south of the border. For economics of scale, Canadian companies wanted access to the U.S. and vice versa.

In terms of technology, provided the window meets the performance requirements of our Codes, for an Ontario builder or renovator it probably makes more sense to use a window manufactured in New York versus one manufactured in Canada on the west coast. (I remember the disturbing story of one Ontario builder who spend tens of thousands of dollars to import windows from the west coast only to find that the process of transporting them over the mountains had caused all the window seals to fail!)

The CAN/CSA A440 standard is gradually being replaced by a new harmonized standard for North America called AAMA/WDMA/CSA 101/I.S.2/A440-8 NAFS –the North American Fenestration Standard. Complete harmonization between the two standards, and the CAN/CSA A440 standard is cited in Code, so for the time being, windows manufactured for the Canadian market also have to meet the Canadian supplement CAN/CSA A440S1-09.

The most striking change introduced in the harmonized standard is the grading of windows for the intended use. This makes sense because windows in tall buildings are subject to higher wind pressures, are more exposed to wind-driven rain, stack effect and other forces. The harmonized standard sets out the following grades of window:

• R – windows designed for single homes or townhouses;
• LC – windows designed for low rise apartment buildings; and
• CW & AW– windows designed for high rise and commercial buildings.

This simplifies the choices based on application, but if you want to drill down, windows meant for the Canadian market also have detailed performance measurements based on either CAN/CSA A440 or the Harmonized AMA/WDMA/CSA 101/I.S.2/A440-8 NAFS Standard with the Canadian Supplement.

Stay tuned for Part II of this feature next week.

An independent building science, engineering and management consultant, with more than 30 years experience, Paul has contributed to Canadian Contractor numerous technical articles about energy-efficient construction, codes and innovations in recent years. His strength is translating technical information into plain language concepts that are easy to understand. He is based in Toronto.

jpaduffy@gmail.com