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Community and Q&A

Pier foundation: floor insulation and HVAC

knb_2001 | Posted in Plans Review on

Hello All,

My wife and I are in the design stages of our new home. We are building 2.5 hrs north of Toronto, Ontario (borderline between a 7a and 6a climate on a forested lot.

I’m a contractor and my business partner is an Architectural Engineering Technician. Our goal is to design and build a 1800sqft 1.5/2 story labour of love that is as efficient and green as our budget will allow.

We are planning a 2×6 wall assembly with 1″EPS and wet-spray cellulose, somewhere in and around R-28.

Due to the shallow bedrock in the area we are leaning towards a pier foundation, which I can complete without having to hire any trades and save on materials, allowing us to allocate these funds to other areas, in theory.

From here one question has spilled into many…How best to insulate the floor with HVAC and plumbing in mind, there are plenty of details showing a simple floor assembly and we can easily meet minimum code, but what is the “best” way to achieve a warm floor that is cost effective and efficient

-Joseph Lstiburek’s article “Bobby Darin and Thermal Performance,” makes sense with forced air, but, are the ducts run through the ceiling and down the walls?

-How about Radiant Water In-floor Heating? Is it as effective in this application? I’m assuming Lstiburek’s detail would not be the ideal in this scenario, possibly a dense pack cellulose with EPS as a thermal break? This option requires some more research on my part (cost, cooling, HRV), but the attraction to radiant is interesting when combined with an outdoor wood furnace.

Thats all for now, none of this is set in stone and I am open to criticism and opinions.

Thanks for your time,


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  1. GBA Editor
    Martin Holladay | | #1

    First of all, the layer of rigid foam you plan to install on your walls isn't thick enough to keep your stud bays above the dew point during the winter. For 2x6 walls, the minimum R-value of exterior wall foam is R-11.25 for Climate Zone 6 or R-15 for Climate Zone 7.

    For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

    For more information on insulating the floor of a house on piers, see How to Insulate a Cold Floor.

  2. user-1115477 | | #2

    You said,
    " Our goal is to design and build a 1800sqft 1.5/2 story labour of love that is as efficient and green as our budget will allow. We are planning a 2x6 wall assembly with 1"EPS and wet-spray cellulose, somewhere in and around R-28.."

    "Green" is a very deep subject, with infinite shades, but just with respect to the best energy efficiency your budget will allow, why not go for passivhaus or passivehouse insulation and air tightness levels, or close to it? I think it has been established that you can recover the somewhat higher construction costs by way of long-term energy savings. Perhaps you have plenty of wood to burn so that you don't burn so much money with heating, but that certainly isn't as green as you could do.

    The 1800 sq. ft. you plan sounds fairly modest (good) and perhaps an ideal candidate to maximize energy efficiency, but keep the building protrusions to a minimum (simple rectangle is best) so that conditioned space is maximized relative to the external surface area exposed. Consider 1 story or 2 story rather than 1.5--not sure, but I think it's hard to maximize the conditioned space/ exposed surface area with a 1.5 story design. However, don't forget aesthetics, altogether.

    I have retrofitted my house to R40 (nominal) walls in the northern part of Zone 4A (tropical, in comparison to your climate) and in retrospect I consider that level just about right. If I were building in your climate, I'm guessing I would build R50 or even R60 walls, although I would run everything through energy software such as the PHPP, BEopt, HEED, etc. (2nd and 3rd are free, and pretty good).

  3. GBA Editor
    Martin Holladay | | #3

    In response to your questions on in-floor radiant heat: the keys to a warm floor are air sealing and insulation. These factors matter more than whether or not you have any hot water tubing under your floor. For more information, see:

    Radiant-Floor Heating

    Goodbye Radiant Floor

    Heating a Tight, Well-Insulated House

  4. Expert Member

    Sonny, although I know many of us wish that it were true, I don't think it has at all "been established that you can recover the somewhat higher construction costs by way of long-term energy savings" by building to Passivhaus standards. There may be many other reasons to do so but the economic argument is far from straight forward.

  5. kevin_in_denver | | #5

    I haven't done it yet, but I've been pondering a SIP floor assembly for a house on piers. Here's the detail:

  6. user-1115477 | | #6

    Response to Malcolm Taylor:

    In most North American climates, it is true that passivhaus (or even close to it, for those who want to argue that it is excessive) construction will easily pay for itself. That is particularly true, now, if natural gas is not available in an area, or not desirable. But you have to want to do it, and not sit around wishing that the masses both understood that and were far-sighted enough to invest in it. Malcolm, I suspect that really is the basis of your response.

    Americans, in general, are still spoiled and non-learning. DOE and building codes are already moving toward passivhaus-like numbers ( I said "toward," not necessarily ever to get exactly there). The building industry moves incredibly slow, as governed by the first sentence in this paragraph. Bottom line: The sun is the energy source and we are being forced to use it more directly--it's happening all around you, just too slowly for you to notice.

  7. GBA Editor
    Martin Holladay | | #7

    Should we be building to a higher standard than minimum building code requirements? Of course.

    Has the Passivhaus standard looked to optimize specifications from a cost-effectiveness standpoint? Absolutely not -- especially since the standard requires builders to follow the same rules in all climate zones.

    So: yes to superinsulation, yes to good air sealing practices, and yes to better windows. But it's important to use common sense (and a good energy modeling program -- PHPP is one option) rather than just aiming for Feist's numbers.

    By the way, the use of solar energy (which you advocate) is not a component of the Passivhaus standard. But PV arrays are increasingly cost-effective, especially in areas with high electric costs.

  8. user-1115477 | | #8

    Not sure of the motive behind your response, but you didn't say anything much different than I did, for the most part. This is particularly true with respect to your third paragraph. I personally believe PH is a good goal and that code will eventually approach it's heating/ airtightness standards (Feist's numbers) in heating dominated climates, but it's not a golden rule--that's why I suggested PH OR something close to it for someone writing from Zone 6/7.

    I won't even argue "cost-effectiveness." Pinning down a standard of cost-effectiveness is like defining "green." It's opinionated, speculative--pick your shade. I've been around a lot of economists, and they can make the numbers say anything you want. No one can even establish universal agreement on the word "cost" in this context, let alone "effectiveness."

    By the way, we all advocate solar energy, not just me, because that's just about all we know, for now. Even the heavier, radioactive fissionable elements are from supernovas. First, if you read closer, I advocate more DIRECT use of solar energy, and we are moving slowly in that direction. Second, while solar energy is not part of passivhaus certification, passive solar design is a perfect match for its energy efficiency concepts, where and when applicable. It's more than a perfect match. Passive solar heating for which the sun sends no bill can contribute significantly to achieving the passivhaus space heating limit--almost as if it was inherent in the certification. I suspect that every passivhaus designer on the planet is at least familiar with passive solar design techniques, uses them when possible, and also recognizes the beauty of "net zero" building design, possibly involving PV--after all, such elements of self-sufficiency are part of the fundamental meaning of the words "passive house."

  9. knb_2001 | | #9

    Sonny and Martin,

    Thank you both for your responses! I've spent the majority of my free time since posting to examine the possibility of building a superinsulated air tight home. We have agreed to a simple rectangular footprint of approx 24'x36' and I'm still leaning towards a 1.5 story home with knee walls to increase headroom and usable area. The attic would be unvented with exterior eps insulation combined with dense pack cellulose.
    Still utilizng a pier foundation with;
    1) rigid insul on the bottom side of the joists with dense pack cellulose; or
    2) built up layers of rigid insulation sandwiched between the first floor deck and a layer of sheathing.

    As for the walls, I have a few different assemblies in mind;
    1) wood cladding, 1/2" air space, 2 layers 1.5" xps, taped and staggered seams, 10" double 2x4 stud, dense pack cellulose, 1/2" airtight gypsum; or
    2) wood cladding, 1/2" air space, 1 layer of Quadlock R-etro ccEPS (3"- R-18, what I'm excited about is their R-26 panel, apparently it's a 3" panel as well???), OSB sheathing, 2x6 stud, Roxul R24 batts, 1/2" airtight gypsum. I'm meeting with the local sales rep for quadlock later this week to go over pricing and confirm the thickness of the R26 panel I haven't been able to find much info on these panels, but they seem user friendly and rigid. Will the interlocking design of these panels be similar to the benefits of staggering layers of rigid insul? What are your thoughts and concerns with this system? Could this act as my air barrier or should I use the zip system?

    As I'm still waiting on rough pricing for both these assemblies, we may have to resort to a third option;
    3) wood cladding, 1/2" air space, 2 layers 1.5" xps, taped and staggered seams, 2x6 stud, Roxul R24 batts, 1/2" airtight gypsum.

    I also like the idea of installing the soffits and rakes after the envelope is complete, although, there are many details to work out.

    The use of ductless mini splits is very intriguing, but with our heating season is there a clear answer on the best and most cost effective supplemental heat source? Is an inline heater with an ERV or HRV a viable solution?

    Thank you again for the support and encouragement, this is a motivating experience.

    Take care,

  10. Expert Member
    MALCOLM TAYLOR | | #10

    Sonny, my response had nothing to do with whether I want to do it or not, or whether it is a good idea. It concerned a completely transparent cost analysis. The additional mark up to bring a structure to Passivhaus standards is not recoverable in energy savings in most North American climates.

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