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Getting the Most out of Windows.

June 07, 2021

By Paul Duffy, M.A.Sc., P.Eng

Photo credit: Unsplash by NeONBRAND

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 aluminum, 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. 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/ CSAA440 or the Harmonized AMA/WDMA/CSA 101/I.S.2/A440-8 NAFS Standard with the Canadian Supplement.

Window performance required in codes varies based on type of building and climate in which it is situated. How do you compare the other measures of performance? Here is a quick primer on how to use the available ratings:

• U-value is the inverse of R-value. A higher U-value represents a higher rate of heat loss. Better windows will have a lower U-value.

• SHGC or Solar Heat Gain Coefficient is the fraction of solar energy passing through the window. A window with a lower SHGC has a greater tendency to block solar heat gain.

• VT is a measure of the visible transmittance of light through the window. The higher the VT, the greater the amount of daylight passing through.

• Air Tightness is measured in classes from A1 through A3, with A3 being the most airtight.

• Water Tightness is measured in classes from B1 through B7. B7 is the most waterproof.

• Wind Load Resistance is categorized with values from C1 to C5. C5 has the highest resistance to wind.

• Resistance to Forced Entry is also broken into groupings; F1 is the minimum level and F2 is the highest level of resistance.

So, you now have information to compare your window options. Can things still get screwed up? Yes, absolutely, because any product can get messed up with a poor installation. Usually, the issues fall into three broad categories:

1. Product selection: I assume that the previous discussion gives at least some guidance on getting your product choices right. It can get complicated, affecting HVAC sizing and other issues. You might want to engage an expert—more about that later.

2. Window sizing: Simply understanding that windows are usually the least thermally efficient elements of your building is an important step. In most new houses, the opaque walls have five to 10 times the thermal resistance (R-value) of the windows and in the summer can be responsible for huge temperature swings affecting comfort and air conditioning loads. Most experts agree that when window areas exceed 15 percent of wall area, comfort problems and other performance problems become more pronounced.

3. Installation: Beyond the windows themselves, the rough openings can be responsible for considerable air leakage and water ingress into the concealed elements of the building. With water comes rot and corrosion. The results can be disastrous. The need for proper training of installers is critical to getting windows that perform.

Recognizing that proper installation goes hand in hand with better windows, most manufacturers participate in a program for training and certifying installers called “Window Wise” provided through SAWDAC – the Siding and Window Dealers Association of Canada. The program provides:

• training of installers;

• random inspections; and

• certifications of installations for warranty purposes.

Most Canadian manufacturers participate in the Window Wise program and support its use. Proper installation of windows could be the focus of a whole other article so, for now, I am going to leave it at installers have to be properly trained.

Window performance also can have a huge impact on heating and cooling loads as well as distribution so I also recommend that major renovations including window replacements be accompanied by an energy/heat loss/gain analysis. If you have ever worked with programs such as the R-2000 Program, EnergyStar, Eco-Energy, etc., you will have some idea of the expertise I am suggesting is needed.

Finally, you may also be aware that window retrofits qualify for some grants and incentives provided by various governments and utilities across the country. You will notice I left this point to the end of this discussion. I don’t think the grants are significant enough to drive customers to change all their windows simply because grants and incentives are available, but there is probably enough money available to help you pay for the experts you need—qualified designers and contractors—to do it right. Most grants and incentives come with a requirement that a qualified expert review and signoff on the installation. I would recommend searching for a local energy evaluator or rater in your area.

In a new house or in a renovation, good quality windows can be the “icing on the cake” that produces stunning results. A high quality window installation can also boost your reputation and referrals. Take the time to do a proper job so your customers won’t be disappointed—deliver high performance that matches the beauty of your work.


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