There is a problem at the centre of Canada's net-zero housing push that almost no one is talking about. It involves the interaction between glazing performance, time, and physics — and it directly undermines the energy model calculations that determine whether a Passive House or Step Code 5 building actually performs as designed over its operational life. The problem is argon gas degradation. And VIG is the only glazing technology that doesn't have it.
How argon-filled IGUs degrade over time
The insulating performance of an argon-filled IGU depends on the argon remaining in the gas cavity. Argon is approximately 34% less thermally conductive than air, which is why it significantly improves U-values over air-filled units. But argon is not permanently sealed in the cavity. Over time, argon diffuses outward through the edge seal at a rate that depends on seal quality, temperature cycling, and UV exposure.
Industry estimates for argon loss in well-made IGUs range from 0.5% to 1% per year under normal conditions. In harsh climates — extreme cold, large temperature differentials, significant freeze-thaw cycling — the rate can be higher. At 1% annual loss, an argon-filled unit that begins at 90% argon fill (a typical specification) reaches 60% argon fill by year 30. At that fill level, the thermal performance advantage over air-fill is substantially reduced.
The PHPP implication: Passive House Planning Package (PHPP) energy models assume stable glazing U-values throughout the building's operational life. If the actual U-value of the argon-filled triple-pane windows degrades from 0.65 to 0.80 W/m²K by year 20, the building's heating demand increases — and the net-zero performance target the model predicted may not be met.
The PHPP modelling challenge
PHPP is the gold-standard energy modelling tool for Passive House certification. It calculates heating demand, cooling demand, and primary energy consumption based on the building envelope specifications entered by the designer. The U-value entered for each glazing unit is treated as a constant.
No current version of PHPP includes a degradation model for glazing performance. The energy modeller enters the manufacturer's rated U-value — typically the day-of-manufacture performance of an argon-filled triple-pane unit — and the model treats that number as accurate for 30, 50, or 80 years of operation. This creates an optimistic bias in net-zero energy projections for buildings with conventional IGU.
VIG does not have this problem. The insulating mechanism — vacuum — does not degrade in the way gas fills do. The getter maintains vacuum quality. The metal edge seal does not permit gas ingress. The performance of a VIG unit at year 30 is functionally identical to its performance at year 1. Delta U over the unit's 15-year rated life: zero.
Weight: the structural cost that PHPP doesn't capture
The energy model doesn't show you the structural cost of triple-pane glazing either. At 28 kg/m², triple IGU is approximately 40% heavier than double IGU and significantly heavier than VIG (approximately 20 kg/m² for 4TL+V+4T). In a Passive House or Step Code 5 project with extensive glazing — often 20–30% of wall area — this weight difference propagates through the structural design.
Heavier glazing requires heavier frames. Heavier frames require larger rough openings and heavier structural lintels. In wood-frame construction, this adds material cost and sometimes requires engineered lumber upgrades. In mass timber or modular construction, the weight implications can be more significant. VIG's lower weight at equal or better thermal performance removes these downstream structural costs.
Novoclimat, R-2000, and Canada's Greener Homes program
Quebec's Novoclimat 2.0 program requires windows with a maximum overall U-value that aligns closely with the performance achievable with VIG. Canada's R-2000 standard — a federal voluntary residential energy standard — has been progressively tightened and now effectively requires triple-pane equivalent glazing performance in most climate zones. The Greener Homes Grant program incentivized window upgrades that meet specific performance thresholds, creating demand for higher-performance glazing that VIG is uniquely positioned to satisfy.
Making the case in a net-zero tender
When a Passive House builder or Step Code 5 developer is evaluating glazing options, the relevant comparison is not just U-value on spec day. It is U-value over 30 years, structural cost impact, documentation quality, and the warranty that backs the performance claim. On all four dimensions, a properly documented VIG specification outperforms conventional triple IGU. VIG Horizon provides PHPP-compatible thermal data, CAN/CGSB compliance documentation, and TÜV Rheinland test reports with every specification package — the documentation set that energy modellers and certification bodies require.
"A net-zero building that uses glazing whose performance degrades over time is not net-zero over its operational life. It's net-zero on day one. The physics don't care about the certificate."
VIG Horizon Inc.