GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Triple-glazed windows and passive solar: Does it make sense to install triple glazing on south-facing windows?

user-1081368 | Posted in Energy Efficiency and Durability on

I live in Southern British Columbia, so we are primarily heating area. No air conditioning required. We have excellent southern exposure, and large overhangs on south side. We plan to install triple-glazed windows on N. E. and W. walls, but not sure if triple glazing makes sense on the South side. Will triple glazing limit winter solar gain?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. CramerSilkworth | | #1

    All the (European) triple glazed windows I've seen recently have SHGCs around 50%. You could find higher with double glazing, but it's more a matter of balancing solar gain with the heat losses. A well designed Passive House doesn't need massive solar exposures (like they used to do back in the 70s for "solar homes"), but they're also super air tight and have high-R enclosures, so the modest SHGC works just fine. What will your walls, roof, and foundation be?

  2. GBA Editor
    Martin Holladay | | #2

    Whenever you specify glazing, you have to make a compromise. Compared to double glazing, triple glazing reduces solar gain. But triple glazing does a better job of retaining heat at night.

    Whichever type of glazing you choose, be sure to order high-SHGC glazing for your south windows. Be careful: not all types of double or triple glazing have a high SHGC. For more information, see these articles:

    All About Glazing Options

    High-Solar-Gain Glazing

    Choosing Triple-Glazed Windows

    To determine the best glazing specifications for your house design and your climate, you'll probably need to use an energy modeling program; one useful program is RESFEN.

  3. user-1081368 | | #3

    Thanks for the input. My insulation values are as follows. Basement slab and walls R-24, Framed walls R-36, Roof R-60.
    My proposed window supplier is suggesting the best Solar Heat Gain Coefficient I will get is 0.18 with a U factor of 0.27 from the tripple glaze that they offer. I have read that I should be getting near 0.20 with a SHGC of 0.40. Is this reasonable to expect?

  4. GBA Editor
    Martin Holladay | | #4

    The SHGC offered by your window supplier is ridiculously low. It is suitable for Florida, not Canada.

    Thermotech Fiberglass Fenestration sells operable casement windows with triple glazing with the following specs: 0.63 SHGC (glazing only), 0.44 SHGC (whole-window). More information here:

    The same company sells fixed casement windows with triple glazing with the following specs: 0.65 SGHC (glazing only), 0.55 SHGC (whole-window). More information here:

  5. user-1136025 | | #5

    You are in southern BC, we are currently building on Vancouver Island and get our triple-glazed windows from Cascadia Windows in Langley. They manufacture fibreglass windows. In 1 3/8" triple-glazed you can get up to a SHGC of 0.56 with a U value of 0.13.

  6. [email protected] | | #6


    Those look like center-of-glass values, not whole window. You might consider asking your supplier what their whole window values are for comparison.

  7. user-1136025 | | #7


    That is right. According to a thermal performance data sheet from the Cascadia website, for their 300 series fixed and tilt& turn windows the thermal performance as per the EN ISO 10077-2 standard in the low-e 180 / clear / low-e 180 configuration, argon-filled, XL Edge spacer is:
    center-of-glass U-factor, fixed: 0.75 (metric) corresponding to 0.13 (imperial)
    total window U-factor, fixed: 0.96 (metric) corresponding to 0.17 (imperial)
    The SHGC also is for center-of-glass but I don't have figures for total window. The decisive factor for us was, we wanted tilt & turn windows in fiberglass and this limited the available selections from the start of course since we also wanted to source as local as reasonably feasible. And Cascadia fits the bill quite nicely.


  8. user-1081368 | | #8

    I have made contact with the Cascadia rep. Thank you for your input.
    Are you able to contact me directly. I am building in Cobble Hill. email: [email protected]
    Thanks again

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |