Home energy efficiency and window installation considerations
My home was built in 1994 with 2×6 walls, though I am unsure of the exact R-value of the insulation used within the wall studs. I live in Calgary, Alberta, Canada (Zone 4a). In August 2024, we were hit by a severe hailstorm, which led to settling with my insurance company. As part of the rebuilding process, I am proceeding with the replacement of my roof, vinyl siding, and soft metals. Additionally, I have decided to upgrade all the windows and doors in our home to triple-glazed units.
Home Background and Energy Concerns
I have owned this home since 2001. It is a four-level split, front to back. One of the most noticeable energy efficiency issues is that when the furnace stops running, it turns back on within 10-20 minutes. To address this, I replaced the furnace with a 98% efficiency natural gas unit and added air conditioning. Additionally, we increased the attic insulation by 14 inches (per the recommendation of a past contractor).
However, the kitchen and living room have a vaulted ceiling with batt insulation that resembles cutting through a hay bale (as I discovered when installing ceiling speakers). Due to accessibility challenges, we did not add insulation in this area. Experts have advised that spray foam would be the best solution, but it would be a significant undertaking.
Despite these upgrades, we have not seen noticeable energy savings. Our electricity and gas bills remain high: $798 in January 2025 and $690 in February 2025 for our 1,600 sq. ft. home. During summer, when the AC is running, it feels like it never shuts off.
Window Concerns
Since purchasing the home, I have known that the existing windows were inadequate. They are slider windows with felt weatherstripping, which does not seal well. A few years after moving in, I noticed the Window seals had failed, leading to condensation forming between the glass panes. These windows have been a persistent issue, and I am now determined to replace them properly.
I suspect that the primary sources of heat loss in our home are the windows, doors, and possibly insufficient insulation within the walls. Given this, I want to take a comprehensive approach to improving the home’s overall thermal performance and try to keep this Project within budget!!!!
Insulation and Window Placement Considerations
Since we are replacing the siding, my installer has recommended adding DUROSPAN GPS R5 insulation to enhance the home’s R-value and improve its thermal barrier. This leads me to an important decision: should we install innie or outie windows?
A high-end home builder advised that innie windows offer better R-value retention and improved protection from thermal shear. He used an analogy comparing it to an Alaskan parka hood: just as a fur-lined hood creates a microclimate that keeps warmth close to the face, an innie window setup helps retain heat and minimizes wind shear. This explanation makes sense to me, but I want to ensure it is the right approach.
If I choose the innie window method, I will need appropriate flashing to accommodate the 1-1/16 inch foam and the vinyl siding.
House Wrap and Sealing Considerations
Another important aspect of this project is house wrap. The same builder recommended using TYPAR because it breathes and allows condensation to escape, unlike Tyvek, which can trap moisture.
For an innie window setup, I assume the process would involve:
- Wrapping the house with TYPAR up to the window openings
- Installing DUROSPAN GPS R5 insulation
- Sealing the joints effectively (Would Tuck Tape be a suitable option?)
For an outie window setup, I would need to:
- Fur out the window to match the DUROSPAN GPS R5 insulation
- Apply the house wrap on top of the foam
One concern with the outie window approach is how to properly secure the house wrap on foam. I do not want the installation crew using a hammer stapler on foam, as this could compromise the material.
Key Questions
- Is an innie window the best choice for improved insulation and thermal efficiency?
- What type of flashing should be used to accommodate 1-1/16 inch foam and vinyl siding?
- What is the best tape for sealing insulation joints—would Tuck Tape be effective?
- If using an outie window setup, what is the best way to secure the house wrap to foam without damaging it?
I appreciate any insights or recommendations that could help make this project as energy/cost-efficient and durable as possible.
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Replies
Rebtech,
I’ll take a stab at some of the questions and leave the ones I'm unsure of for others.
- You are actually in climate zone 6.
- I’m not sure the marginal gains from moving the windows in are worth the complication of finishing the openings.
- Typar is 11.7 perms, Tyvek is 77 perms, and Tyvek Commercial is 28 perms, so your builder has this backwards.
- You should use the proprietary tape of whatever house-wrap you choose.
- Use cap-nails to secure the house-wrap though the foam.
Have a read at this.
RebtTech,
"The same builder recommended using TYPAR because it breathes and allows condensation to escape, unlike Tyvek, which can trap moisture."
As I said, this is flat out wrong. What they call "breathing" is the permeance of the material, and Typar has a lower perm rating that Tyvek.
The argument Typar makes is a bit different. They say their product is more robust, so it lets less bulk water though it. I agree. That's why I use a similar product - Tyvek Commercial - rather than regular Tyvek.
I agree with Malcolm: I think the R value difference moving a window between the three positions (innie, outie, and "inbetweenie") is negligible. I personally think outies generally look better, and they're also easier to flash/detail.
Your R5 exterior rigid foam is really too thin for your climate zone. You want R11.25 for CZ6. I'd try for AT LEAST R10 here, which would be 2" of GPS. That's not really all that difficult to do. I reference Martin's classic article on the subject: https://www.efficiencyvermont.com/Media/Default/bbd/2019/docs/presentations/efficiency-vermont-bbd-rethinking-the-rules-on-minimum-foam-thickness.pdf
My guess is that you probably need to put some effort into air sealing. Air leaks can easily cancel out other efficiency improvements. I'd look at the classic spots first, which includes the window weatherstripping you already mentioned, but also attic access hatches/doors, recessed lights -- especially those on upper levels directly under an attic -- and any penetrations you're aware of. A blower door test can help you find any hidden leaks.
Bill
Rebtech,
Bill is right that the foam is too thin, but I think a couple of things mitigate the risks in your case.
- Calgary is dry. Things work there that don't in most other climates.
- Like most Canadian houses I'm pretty sure your walls include a poly vapour-barrier.
That said, I'd do as much air-sealing as I could, including detailing the sheathing as an air-barrier.
Malcolm, is that poly vapor barrier required by code in all provinces? I know it is in Ontario, but I have pretty much zero experience anywhere else -- I'm really a US based contractor after all :-)
Bill
As far as I know poly before drywall in Alberta it's required by code. They recently add a new code where all electrical outlets (inside of house) that are on a exterior walls must have plastic outlets like the picture I added. It's a insulation and vapor barrier code.
You are allowed to use steel boxes and vapor hat barrier so long as they make a flange on all 4 side to allow a tight press against the poly and acoustic seal.
Bill,
No, it's a misconception that any Canadian building codes require poly. However it is still the overwhelming choice for an interior vapour-barrier in most of the country.
The codes call for a vapour-barrier “sufficiently close to the warm side of the assembly to prevent condensation at design conditions". It can consist of any material less that 1 perm (our definition of a vapour-barrier, which is a class 2 vapour-retarder in the IRC).
Thanks, everyone, for your input!
I just received my report and have attached it to this post. However, there are some parts I don’t fully understand—would anyone be willing to give me the key takeaways?
From what I’ve read in the PDFs, windows and doors seem to be a major factor. I also plan to replace the exhaust fans (two bathroom fans and the oven hood fan), assuming there are Energy Star-rated units available.
Regarding upgrades to the furnace, water tank, and HVAC, I might consider those in the future when they near the end of their lifespan, as I only installed them a few years ago.
One of the PDFs suggests that adding exterior foam insulation may not provide much benefit—or am I misinterpreting this? If I decide to move forward with it, I’ll upgrade to GPS R10 and have my contractor remove the soffits to install foam all the way up. I’ll also have the window installers fur out the casings to 2" for a simpler install and cleaner finish. If this approach saves me money, I’m all for it.
I also have a question about the existing tar paper that was installed in 1994—should I leave it in place or remove it before installing the foam insulation?
Lastly, with the 2" foam installation, I anticipate some challenges with existing structures. I have four 4x6 posts against the house—one supports a gate, and the other three are part of a small side shed (just posts and a roof). These wouldn’t have been an issue with 1" foam, but with 2", they could interfere with installation. Would it be better to trim the posts down or adjust the foam thickness in those areas and wrap the siding around them?
Any recommendations would be greatly appreciated!