NAFS / CSA A440 Ratings: Air, Water & Wind Performance

Every window installed under the Quebec Construction Code carries a NAFS label, and almost nobody outside the industry can read it. Its letters and numbers tell you how much air leaks through the unit, how much wind-driven rain it holds back and what wind pressure it survives before something bends. Here is what each rating means, how Quebec's supplement sets the minimum for your region, and how to use the label to compare two quotes on equal terms.

What NAFS and CSA A440 actually are

NAFS stands for the North American Fenestration Standard/Specification, published jointly under the designation AAMA/WDMA/CSA 101/I.S.2/A440. It replaced the older Canadian CSA A440 window standard in 2008 and is now the single test method for windows, doors and skylights across Canada and the United States. Because Canada's climate and building traditions differ, CSA also publishes the Canadian Supplement, CSA A440S1, which tells you which NAFS rating a given building in a given town actually needs.

The National Building Code, and with it the Quebec Construction Code (Chapter I – Building), references NAFS and A440S1 for houses and small buildings. A window sold for new construction or a permitted replacement in Quebec must therefore have been tested to NAFS by an accredited laboratory and labelled accordingly. The label is a certification of physical performance: it says nothing about energy efficiency, which is governed by a different standard, CSA A440.2, and shows up as U-factor, SHGC and Energy Rating figures instead.

NAFS has been updated several times — 2008, 2011, 2017 and 2022 editions exist — and provincial codes adopt a specific edition with some delay. The ratings vocabulary has stayed stable, so the explanations below apply regardless of which edition your manufacturer's report cites. If a quote references an edition, that is a sign the seller has actually read the report.

Performance Class: R, LC, CW and AW

The first item on a NAFS label is the Performance Class, which defines the family of tests the product went through and the minimum grade it had to reach. R (residential) starts at a Performance Grade of 15, LC (light commercial) at 25, CW (commercial window) at 30 and AW (architectural window) at 40. Each step up also raises the water-penetration test pressure relative to design pressure and adds requirements — tighter deflection limits, operating-force limits, life-cycle testing for some products — that matter in a 20-storey tower and rarely in a bungalow.

A class is not a quality medal on its own. An R-class casement rated PG50 has survived more wind pressure than an LC-class casement rated PG25; what the LC class buys you is a tougher water test and stricter durability checks at a given grade. For a detached house or a two- or three-storey plex in Quebec, R and LC are the normal classes, and a well-built PVC window from either class can meet the code minimum with margin. CW and AW show up on exposed sites, tall buildings and institutional work.

Read the class and grade together, and then look past them at the individual test results, which are where two windows of the same headline rating can differ a great deal.

• R: residential; minimum PG15; the baseline for houses and small plexes
• LC: light commercial; minimum PG25; tougher water test at the same grade, common on quality residential lines
• CW: commercial; minimum PG30; deflection and durability requirements for mid-rise buildings
• AW: architectural; minimum PG40; heavy-duty, institutional and high-rise

Performance Grade and design pressure

The Performance Grade, written PG followed by a number, is the design wind pressure the window is rated for, expressed in pounds per square foot. PG30 corresponds to a design pressure of about 1,440 Pa, PG40 to about 1,920 Pa and PG50 to about 2,400 Pa (1 psf equals 47.88 Pa). Design pressure is not the pressure the window was pushed to in the lab: the structural test applies 1.5 times that value, in both directions, and the window must show no glass breakage, no hardware failure and no permanent deformation beyond a small allowance once the load is removed.

Because the label is a pass/fail at a chosen grade, a manufacturer that tests to PG30 may well have a product that would pass PG40 without having paid to prove it. Some labels also carry a separate design-pressure figure, for example when a product exceeds the structural requirement of a higher grade but not its water test; treat a DP number as structural information only and keep the PG as the official rating.

A quirk that catches many buyers: NAFS ratings are tied to the size that was tested. A casement rated PG40 at 750 by 1,500 mm does not automatically cover a 900 by 1,800 mm version of the same series, because the larger sash deflects more under the same pressure. The report lists the tested size, and a conscientious supplier confirms that your largest unit falls within it or has a separate test.

Air infiltration: A2, A3 and 'Fixed'

Air leakage is measured with the window closed and locked under a pressure difference of 75 Pa, roughly what a 40 km/h wind produces on a wall. NAFS itself sets a baseline for R and LC products of 1.5 litres per second per square metre of window area. The Canadian Supplement keeps the older, more discriminating classes that Quebec buyers know: A2 allows up to about 1.65 m³ per hour per metre of sash crack, A3 up to about 0.55 m³/h per metre — three times tighter — and a Fixed class, around 0.25 m³/h per metre, applies to non-operable units.

In a Quebec winter, the difference between A2 and A3 is felt, not theoretical. At -25 °C with wind, an A2 window on the exposed side of the house produces a cool draught you can find with the back of your hand, and the leaking air brings the interior glass edge closer to the temperature where condensation forms. Compression-sealed casements and awnings reach A3 almost as a matter of course; sliders and double-hung windows, whose sashes slide past a brush seal, are more often A2. If two quotes differ on this class, that is a real difference in comfort and heating cost.

Air tightness also feeds directly into the Energy Rating printed on the energy label, since the ER formula subtracts a penalty for leakage. That is one of the few places the structural label and the energy label overlap.

• A2: code-acceptable; about 1.65 m³/h per metre of crack at 75 Pa
• A3: the level to ask for in Quebec; about 0.55 m³/h per metre — typical of casements and awnings
• Fixed: non-operable units; about 0.25 m³/h per metre

Water penetration: the test that separates good frames from great ones

In the water test, the laboratory sprays the outside of the window at a calibrated rate — about 3.4 litres per square metre per minute, a heavy rain — while applying a static pressure difference across it, and then repeats the exercise with cycling pressure. The window passes if no water reaches the interior face of the frame during the test period. What differs between products is the pressure at which they pass, and that is the number printed on the label, in pascals.

NAFS ties the water test pressure to the design pressure: 15 percent of DP for R and LC products, with minimums of roughly 140 Pa for R and 180 Pa for LC, and higher floors for CW and AW. A PG30 window in the R class is thus tested at about 220 Pa, but many manufacturers test water separately and label a higher figure. In Quebec, where autumn storms bring rain almost horizontally off the river, a water rating in the 220 to 300 Pa range is a comfortable target for a house; exposed sites in the Gaspésie, Côte-Nord or Bas-Saint-Laurent justify more.

Two cautions. First, the water test proves the window, not the installation: a 300 Pa window set without proper sill and head flashing will still leak, just around the frame rather than through it. Second, some products pass the water test with the sash locked but not with the sash merely closed — a detail buried in the report that explains why a poorly latched casement drips in a storm.

How Quebec's CSA A440S1 supplement sets your minimum

A440S1 turns the NAFS menu into a requirement. It starts from the climatic data that the building code publishes for each municipality — the one-in-fifty-year hourly wind pressure and the driving-rain wind pressure — and adjusts for the building's height (above or below about 10 metres), its terrain exposure (open country and shorelines versus built-up urban areas) and whether the window sits in a corner zone, where wind pressures peak. The result is a minimum Performance Grade and a minimum water test pressure for that building.

For a low-rise house in the Montreal area, the hourly wind pressure is in the order of 0.40 to 0.45 kPa, and the supplement's tables typically land at a required grade in the PG20 to PG30 range, with a water test pressure in the low hundreds of pascals. The same house on an open lakeshore in the Laurentians or on the St. Lawrence in Lévis moves up a notch; a three-storey plex on a corner lot moves up another. The figures vary by municipality, so treat these as orientation, not specification — your supplier or designer should quote the table value for your address.

Municipal inspectors in Quebec rarely check the label on a replacement window, but insurers and warranty adjusters do read test reports when a claim involves wind or water. Meeting A440S1 is therefore not just a code exercise; it is what makes a manufacturer's water-infiltration warranty enforceable.

• Start from the climatic data for your municipality (hourly wind pressure, driving-rain wind pressure)
• Adjust for building height and terrain: open or shoreline sites and taller buildings need more
• Corner windows on the upper floors carry the highest required grade
• The result: a minimum PG and a minimum water test pressure specific to the building

How to compare two windows using the label

Put the two labels side by side and go through them in a fixed order: class and grade, water test pressure, air class, tested size. Suppose window A reads R – PG35 – Water 260 Pa – A3, tested at 900 by 1,500 mm, and window B reads LC – PG25 – Water 180 Pa – A2, tested at 600 by 1,200 mm. For an 800 by 1,400 mm casement on a Montreal house, A is the stronger product on every axis that matters, despite B's more impressive-sounding class — and B's rating does not even cover your size.

Ask for the test report, or at least the certification summary, rather than the brochure. A brochure often quotes the best result from the whole product line; the report tells you which frame, glass thickness and hardware produced it. Check that the rating applies to the configuration you are buying: combination units such as a picture window with flanking casements, or a window over a transom, are rated as assemblies, and the mullion between them is frequently the weakest structural element. Bay and bow windows are combination assemblies by definition.

Finally, compare the same window type. A fixed unit will always show lower air leakage than an operable one, so a supplier who quotes the fixed-unit result for a mixed order is not lying but is not being helpful either. Our full range of PVC windows is tested to NAFS, and we provide the report for the specific series and size you are ordering.

• Class and grade: same or better than the A440S1 requirement for your address
• Water test pressure in pascals: higher is better; 220 Pa or more for most Quebec houses
• Air class: A3 for operable windows, especially on the windward side
• Tested size: at least as large as the biggest unit on your order
• Configuration: combination assemblies rated as assemblies, not as their individual parts

Not the same thing as ENERGY STAR or the Energy Rating

NAFS measures air, water and structure. It does not measure heat loss, solar gain or condensation resistance, which come from CSA A440.2 and appear as U-factor, SHGC, ER and — where the product qualifies — the ENERGY STAR mark. A window can carry an excellent energy label and still be A2 on air leakage; it can be A3 and PG50 and still have a mediocre U-factor because of ordinary double glazing. Both labels exist because both properties matter, and Quebec's code has requirements on each side: the energy provisions in Chapter I.1 and the A440 provisions in Chapter I.

When you are comparing quotes, the practical shortcut is this: the energy label tells you what the window will cost you to live with in January; the NAFS label tells you whether it will still be doing that job, dry and draught-free, in twenty years of Quebec wind and rain.

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