GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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

How would YOU insulate my new house given the conditions?

nfiorito | Posted in Energy Efficiency and Durability on

This is my first post on GBA but I think I’ve read every article on the site in preparation for building our new home, located in Thunder Bay, ON, Canada (40 minutes north of the Minnesota border, Climate Zone 7). I’ve learned a lot here, but like other posters have suggested, I might be MORE confused than when I started!

Background: I’m seriously considering fully off-grid PV electricity and ground-source heat pump with DHW capability and have quotes coming back for these items, as our home is located on a hilltop 300m (~1000′) from the road and power lines, and bringing power in will be almost as costly as an off-grid system. We have 100 acres. No natural gas available either; my two neighbours in brand new homes use propane-fueled forced air furnaces (something I’m not too keen on doing).

We also just came through the coldest February of all time here at an AVERAGE of -19.6*C, but yesterday was +12C, to give you an idea of the weather and temp swings we face.
At any rate, I’m planning a 2×6 PWF basement and 2×6 walls, as I’ll be doing the work myself along with after-hours help from two carpenter friends.

The home has large south facing windows with a walkout basement and as Thunder Bay is quite sunny (no city East of us in Canada gets more sunshine), I think we’ll have nice solar gain into the home during the winter. Google “max fulbright asheville mountain” and that’s the plan we’re using, with some modifications like an additional mudroom/laundry on the side, fewer basement windows, and covered porch on half of the front.

All this to say, if you were me, what would your wall assembly look like for basement/foundation and upper floors? There will be no air conditioning as we’re fairly windy on the hill and the cooling season is short here. I am also considering plywood over OSB on the north side.

I really like the idea of using Roxul in the cavities and mineral wool panels (Roxul Comfortboard IS) on the exterior to account for thermal bridging, but am wondering if I still need to observe the dew point requirements for exterior insulation (R15 for my area) with this system as the panels can breathe (vs. rigid foam)? I’m not too excited about installing windows and flashing over 3+” of exterior foam. I also would need an interior poly vb with this option.

OR – would this be a situation where 1.5″ taped T&G interior rigid foam over mineral wool batts in the cavities could also work as a VB and thermal break? This would allow me to avoid poly vapour barrier and flash the windows against the exterior sheathing (OSB, most likely). I know this method (interior rigid foam) is less favoured here, but I’m thinking it might work?

Other options, configurations and suggestions are welcome! Budget is of course always a concern but top priority is performance and ease of quality install. 2×6 framing is pretty much decided on, however. Also, one of my new neighbours also owns the local spray foam company, so a batch of fresh cookies and a knock on the door may bring that option into play as well. Maybe my best option then would be spray cavities and mineral wool panels on the exterior? Dew point concern with this?

Sorry for the long-winded description, and thanks in advance for any insight you can provide; would love to hear your thoughts!


  1. nfiorito | | #1

    *Sorry, should have added that the exterior will be vinyl (or hardi if budget allows) with 3' of stack-stone at bottom.

  2. GBA Editor
    Martin Holladay | | #2

    You can't operate a ground-source heat pump with an off-grid electrical system. When you get a week of cloudy weather in December, there is no way that your battery system can power your heating system.

    There are just three ways to heat an off-grid house:
    1. A wood stove.
    2. A propane space heater with a through-the-wall vent.
    3. An old-fashioned oil-fueled parlor stove with gravity-feed fuel delivery from an elevated oil tank.

  3. user-2890856 | | #3

    W/W Heat pump with propane backup possibly or even oil . Solar thermal storage has moved into the 21 st century also . You could easily enjoy COP over 5.5 during heat pump operation . Possibly a diesel generator as electric back up just in case the sun doesn't shine .

  4. LucyF | | #4

    I don't understand the need for the poly vapor barrier - is it because it's code? The truth is I don't really understand the need for a vapor barrier at all (not just on your house). Shouldn't we just be doing air barriers? There are a number of air barrier materials that allow drying to either side that would work better, I think. Some examples are MemBrain from CertainTeed, Intello from Pro Clima (distributed by 475 Building supply in the US) and Siga Majpell from Small Planet workshop.

    I really like Roxul as insulation. You can't beat it for fire resistance. It's dense and fills the cavity well if done properly. I also really like the Roxul Comfortboard (we used Roxul Rockboard 80 which is the same thing essentially, just easier for me to find) as well. I'm guessing you don't have much problem with carpenter ants or termites so the insect resistance probably doesn't as matter much to you.

    If your walls can dry in both directions with a more vapor open air barrier and Roxul insulation on the exterior and interior of the walls, do you really have to worry about dew point with your sheathing? I'm asking this question for the more numerically inclined advisors like Martin and Dana.

    Your question is much like Andrew Bennett's in a recent thread ( My opinion as a non-builder (mostly all I've done is designed how we were going to build my brother's house in terms of insulation, air barriers, wall thickness, etc.) is that you just have to pick what you think you can build or have built the easiest. In other words, build what you think you can best convey to the people helping you build a house. For example, I did not do double stud walls because I couldn't conceive of all the details with installation of doors and windows, which one was the weight-bearing wall, figuring out where the air barrier was, etc, etc. I could probably do it now, but I could not think it properly 2 years ago when planning the house.

    The other option is to run the proposed wall designs through some program like the Passive House Planning Package. My understanding is that you can actually figure out what makes the most financial sense from using that spreadsheet. I don't live in an extreme environment - Upstate SC. I didn't think that was necessary for the house we built here, but it is probably more critical where you live.

    Also what is your desired R-value for your walls? 2 x 6 walls and 2 inches of Roxul Comfortboard don't really get you very far for zone 7. R 28-30?

    I thought it was a blast planning and building the house. I'm trying to figure out which family member needs a house so I can do it again. I may have to content myself with retrofits from now on though. Have fun with your project.

  5. GBA Editor
    Martin Holladay | | #5

    Richard, how long have you lived off-grid? You're wrong. It's nuts to run a heat pump with a fossil-fuel powered generator.

  6. user-2890856 | | #6

    Martin ,

    Just as nuts to attempt to build a large enough battery for PV during those times that that bright thing is not up in the sky . Hydronic solutions are readily available to store plenty of water at a temp that would heat a well built home for quite a long time with properly sized storage and controls . It is a shame that you are unaware of these things or just discount them .
    So you would rather continue down the same path and never explore other options because someone wrote an article many years ago that may or may not be totally accurate ? As I have stated many times before , there is no lack of poorly designed systems by rep agencies , contractors , and the like . Generator back up is very reliable .

  7. GBA Editor
    Martin Holladay | | #7

    There is no need to lecture me about generator backup; I have been living with a generator for 22 years. Before that, when the sun didn't shine, I went back to kerosene lamps.

    Of course generators can produce enough electricity to power a furnace or the circulators and burners required for a hydronic heating system. But experienced off-grid homeowners know that running a generator to operate a heating system that requires electricity is a noisy and expensive way to get through the months of November, December, and January.

  8. user-2890856 | | #8

    My remark was based on this statement Martin .

    " The home has large south facing windows with a walkout basement and as Thunder Bay is quite sunny (no city East of us in Canada gets more sunshine), I think we'll have nice solar gain into the home during the winter. Google "max fulbright asheville mountain" and that's the plan we're using, with some modifications like an additional mudroom/laundry on the side, fewer basement windows, and covered porch on half of the front. "

    Is it possible that backup won't be needed all that often ? Kerosene lanterns are great during a disaster or walking through the woods . Depending on them as lighting because you chose to live off grid and neglected to install sufficient backup resources is choice but not one I would consider prudent . As far as safety is concerned I think it is downright dangerous , STUFF HAPPENS .

    Maybe with 100+ acres there is somewhere to locate a generator that noise won't be an issue ? Maybe they now make generators that are much more quiet than the one you and other off gridders have ? Quality hydronic systems designed for this specific type of home do not require alot of electricity anymore Martin . Could probably build one with less than a 1 KWh requirement . Of course the heat pump would not operate during those times and backup may be oil or propane source .

    My off grid is a bit different than yours but trust me I am off grid quite enough . I also fail to see anything approaching what one might consider a lecture .

  9. GBA Editor
    Martin Holladay | | #9

    You apparently misunderstood my point. I am not advising Nik to build an off-grid house. On the contrary: I would strongly advise Nik to build a grid-connected house.

    It's true that when I bought my first PV module in 1980, I didn't have enough money to buy a generator. I am not urging anyone to emulate my technology choices, nor am I defending them.

    I stand by my advice that for an off-grid house, the only heating systems worth considering are heating systems that don't require electricity. When off-grid homeowners ignore this advice, they usually abandon the expensive heating equipment that requires electricity within one or two years.

  10. nfiorito | | #10

    Thanks for the input so far, everyone!
    Additional thoughts:

    Nothing is set in stone right now, quotes are out for the GSHP and off-grid system. Again my neighbours run propane FA furnaces and power from the utility, so those are worst case options, but available (and I'd rather do a bit better than worst case). I have also looked at an outdoor wood boiler for heat and DHW, but am on the fence about going that route as we take longer vacations in the winter at times, and we're trying to keep recurring costs low (hence the power from the sun and heat from the ground thought). I do have three boys that would be helpful when it comes to gathering and loading wood though!

    I was planning on adding a propane generator to the system if I do go off-grid, as the kitchen range, BBQ, and clothes dryer will be propane, so I'll have a tank on site anyway. I am also on a windy hilltop, so a turbine could also be added for cloudy-day insurance, but then I'm getting up there in price on the whole system.

    Poly is the rule around here, not the exception it seems. That being said I am meeting with the building inspector on Monday and could see how high his eyebrows rise at the mention of omitting it. I am still wondering along with Lucy if dew point calc's are necessary with MW panels on the exterior?

    Put it this way: you have $60k to account for heat, hot water, electricity and insulation and you are building for a family of 7 people 1000' off the road with no natural gas - what would you do?

  11. wjrobinson | | #11

    Honda cogeneration

    No noise
    Yes heat
    Yes electricity
    No noise
    Long life

  12. GBA Editor
    Martin Holladay | | #12

    As far as I know, that cogeneration unit is no longer available. The U.S. distributor (Freewatt) went out of business.

  13. nfiorito | | #13

    Anyone with ideas on insulation? I feel my off-grid aspirations have derailed my main question!
    Dew point calc's with mineral wool? Or not necessary if the exterior insulation can breathe (vs foam)?

  14. GBA Editor
    Martin Holladay | | #14

    Most green builders would probably choose to insulate basement walls on the interior with EPS; 3 inches will give you R-11 or R-12, while 4 inches will give you R-14 to R-16.

    For above-grade walls, the two main choices are (1) double-stud walls (usually about 12 inches thick) insulated with blown-in cellulose, blown-in fiberglass, or mineral wool, and (2) 2x6 walls with exterior insulation (either EPS or mineral wool).

    If you use mineral wool for exterior insulation over a 2x6 wall, you don't have to worry about the minimum thickness issue, because mineral wool is vapor-permeable. That said, walls with a higher R-value always perform better than walls with a lower R-value.

  15. wjrobinson | | #15

    Trying to have a tight budget, then fiberglass batts and cellulose and reclaimed foam are your options.

    Martin, cogen MCHP for home use is pretty ephemeral indeed.

  16. nfiorito | | #16

    Thanks Martin,

    Just to confirm then that EPS will not promote condensation issues if the exterior of the PWF foundation is covered with blueskin and dimpled membrane, because the EPS has a high enough perm rating? (Therefore avoiding an impermeable sandwich situation for the Roxul in the cavities?)
    My current leanings then would be:

    Basement from exterior: Dimpled membrane for protection and drainage > blueskin > Plywood > 2x6 cavities with Roxul > 2-4 inches EPS > drywall > paint

    Above grade from exterior: Vinyl or other lapped siding > furring strips > 2" rigid mineral wool panels > Tyvek > OSB > 2x6 cavities with Roxul > (Poly or no poly depending on inspector) > drywall > paint

    I suppose the Tyvek might go on top of the MW panels on the exterior if I do "outie" windows, which I think I'd prefer.

    Thanks again for the help!

  17. GBA Editor
    Martin Holladay | | #17

    Wood foundations are hard to insulate; I didn't realize that you are planning a wood foundation.

    I don't think that it ever makes sense to install an air-permeable insulation like mineral wool on the interior side of the cold plywood of a wood foundation. If you get condensation against the cold plywood, water can trickle down the plywood and form puddles at your bottom plate.

    The only interior insulation I can recommend for this type of foundation is closed-cell spray polyurethane foam.

    Of course, you can always insulate the plywood on the exterior (with mineral wool, EPS, XPS, or closed-cell spray foam).

  18. Expert Member
    Dana Dorsett | | #18

    Definitely insulate the wood foundation from the exterior, which will keep the wood warmer and drier.

    FreeWatt (Climate Energy) didn't go out of business- they sold the business to ECR International, who supported the product for a few years, but apparently didn't find the sales growth rates compatible with their business model or shareholder expectations or something and dropped it. Honda still makes ~1kw natural gas & propane generators, which saw a HUGE uptick in domestic sales in Japan in the wake of the Fukushima disaster.

    The existing installed base of Freewatt systems are still being supported in the US (I only know this only because my biz-partner has one humming away quietly in his house). When the Honda has run xxxx hours the support group knows before the homeowner does (it's an internet connnected system), and when it's time to change the oil or tune it up they get in touch to schedule the maintenance. They are also able detect any number of functional problems remotely. But SFAIK the Honda cogenerators have never been sold & supported as standalone sytsems in north America, but there are many tens of thousands of standalone installations in Japan (both grid-tied and off-grid).

    As of 2011 there was an installed base of over 100,000 grid tied "EcoWill" and "EcoWill-Plus" units running in Japan, and the product has been improved since then. The Plus versions are design to normally grid tied, but off-grid capable (with a handy pull-rope starter). It's probably possible to grey-market import an EcoWill Plus into Canada for an off grid application, but it's probably not a good fit for an Ontario climate- in the much more temperate climate of Japan they are usually mounted on the exterior of the house, which would have serious freeze-up potential in that configuration. (It's probably able to handle coastal British Columbia type climates though), but it's probably adaptable for mounting inside of conditioned space. See:

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |