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Community and Q&A

North Idaho ranch house design

user-6258531 | Posted in Green Building Techniques on

Our house will be around 1800 sq ft with a 600 sq ft attached garage. In northern Idaho, zone 6.

The plan is to build slab on grade due to water table issues in my subdivision.
Heat would be hydronic in floor heat. High efficiency natural gas boiler which would both supply hot water to floor and heat domestic hot water. Looking forward to no forced air noise or dust. We have Natural Gas service at street.

Not planning to add Air Conditioning. N Idaho seems to cool down sufficiently at night that one should be able to use a whole house fan to cool the house down enough to not need AC. From what I could see, there were only two nights this summer where that strategy might not have worked. I might run the electrical to spots where I’d add mini splits units just in case I’m wrong about this. From reading on this site I learned that I need to consider the cost of the hole in the ceiling with a whole house fan. I’m evaluating Energy Star cool roofs as a way to help with keeping the house cool.

I plan to insulate under the slab with 4 inches of XPS foam.

The ceiling will be as close to R 60 as I can get. Will use either energy trusses or cantilevered trusses to get significant insulation out to the wall top plate. Does blown in cellulose seem the best choice for that? Is there anything I should consider given that I will have a 2250 cfm fan blowing into the attic space in the summer?

Haven’t decided walls yet. Certainly will be 2X6. May add external rigid foam although that seems to complicate a lot of other things like installing windows and siding. I did a return on investment for adding rigid foam and other potential insulation options. The spreadsheet is attached. I welcome feedback to improve on my installed cost and effective R values. The best upgrade from starting point of R 19 batt seems to be blown fiberglass like Spider with an inch of Polyiso on the interior. Best from an ROI standpoint that is.

My biggest question is would additional money be better spent on other areas than increasing wall R Value? A couple of areas I’m still researching are reducing air infiltration and better windows.

I am not sure how to spec the caulking and sealing of the house, but I certainly want to reduce air infiltration. Is there some standard language to use in a contract with my builder? Assuming I reduce air infiltration sufficiently, I’m thinking about using the Twin Fresh Comfo units. Not sure yet if I need two or four. I like them as they don’t need ducts.

Will spec air tight electrical boxes, use air tight LED ceiling fixtures in place of can lights, etc. No ROI analysis needed for the air tight LED’s, I think it is great technology and currently own a house with can lights and little attic insulation. What an energy waste.

My starting point is to use North Energy Star windows, mostly single hung and casement. Looks like one can get an U of .27 in double pane. I’m looking at windows that have a higher SHGC especially for the southern exposure. Suggestions of a triple pane window with low air infiltration to use for my window ROI would be appreciated.

I will likely add at least 6 kW PV system. Even with so-so net metering in Idaho ROI is 3% without assuming any increase in electrical rates. I’m investigating how to make provisions for future addition of panels up to 8 kW system as I hope to be able to purchase a reasonably priced plug-in hybrid SUV. When will that Mitsubishi Outlander ever arrive in the US???

My contractor is open to my ideas for energy improvements but is not a “green builder”. The only “green builder” in the area didn’t want to bother with my project as they are able to land projects that cost twice or more what mine will. Can’t blame them for that, I would do that same. But it does leave me trying to figure out a lot of this stuff on my own. Fortunately I’m into it and I have this great site as a resource.

Any ideas to help me make this a greener house appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Will use either energy trusses or cantilevered trusses to get significant insulation out to the wall top plate."

    A. You need to figure out how many vertical inches you need between the top plate of your walls and the underside of the roof sheathing -- don't forget to account for the required ventilation gap and the thickness of your ventilation baffle -- and then convey that information to the truss manufacturer. If you don't tell them what you need, they can't build it for you.

    Q. "Does blown in cellulose seem the best choice for that?"

    A. In my opinion, yes.

    Q. "Is there anything I should consider given that I will have a 2250 cfm fan blowing into the attic space in the summer?"

    A. Of course. You need a good way to seal the fan opening every winter -- which means that you will need to build a weatherstripped R-60 cap that is moveable. Warning: this cap will be heavy. You will also need to make sure that your attic has adequate ventilation openings to allow the air to escape when the fan is running. For more information, see Fans in the Attic: Do They Help or Do They Hurt?

  2. Reid Baldwin | | #2

    One suggestion for building a greener house is to rely less on ROI calculations. For a candidate design change, estimate the energy savings (including embodied energy), or the CO2 savings. Balance that against the cost (initial cost minus present value of operating cost savings). Excessive reliance on ROI indicates that you don't value greenness directly, but only value the associated cost savings.

  3. Expert Member
    Dana Dorsett | | #3

    The 4" of XPS under the slab will drop from it's labeled R20 will drop to R16.8 over a few decades. The 20 year or lifetime warranties may indicate that it drops to only R18, but they are pretty much counting on the fact that nobody is going to be disassembling the house and having samples tested in certified labs to collect on those warranties. From a design point of view it's more appropriate to use it's fully depleted performance (about R4.2 per inch), which is after it's blowing agents have fully dissipated.

    If you want R20 performance over the lifecycle of a house it needs to bumped up to 5", or you can use 5" of Type-II EPS instead. Given the drastic difference in environmental impact between the HFC blowing agents used for XPS and the pentane used for blowing EPS, the latter is hands-down the greener choice. In the unlikely case that the water table is right at the bottom of the foam layer, it may have to be 6" (labeled R25) to account for some performance hit from the interstitial spaced being filled with water, but with a code-legal drainage bed of gravel under the slab 5" is really all it takes. It's cheaper than 4" of XPS too.

    Lose the R19s in the analysis they're junk, barely more than an air filter, performs at only R18 when compressed to 5.5" in a 2x6 cavity, are insufficiently air-retardent to prevent convection loops within the cavities, and do next to nothing for slowing air infiltration from any leaks. An R19 batt is what you get when you fluff an R13 batt up to 6.25" of loft.

    R23 rock wool has value beyond the mere energy cost savings, since it provides a significantly better resilience value in a fire situation than fiberglass insulation.

    Similarly, exterior foam of R11.25 or higher offers a moisture resilience factor, beyond mere energy savings. To get there with lower cost lower impact low density Type-I EPS it would take 3", but 3" of Type-I EPS is usually substantially cheaper than 2.5" of XPS. You can also get there with only 2.5" of Type-II EPS since the labeled R-value at 40F would be R11.25, and during the months that matter from a moisture accumulation point of view it would be at a lower mean temp and higher performance point than R11.25 You could also get there with 2.5" of polyiso as well, but that would be more expensive. Despite the 75F mean-temp labeled R value you can get there with just 2" despite the labeled R-value, since polyiso needs to be derated to about R5/inch when on the exterior in your climate.

    Given the quantity of slab-foam and the potential wall foam the quantity is high enough that you can probably get there at an extreme discount by going with reclaimed roofing foam from building materials recyclers. In my area it's possible to get reclaimed Type-II EPS or fiber-faced polyiso at 60-75% discount below distributor pricing on virgin stock goods from multiple vendors. One of those vendors ( Nationwide Foam: ) has depots within affordable-trucking distance of most of the lower 48 states. When using reclaimed foam, order 10- 15% more than needed to cover for any damaged goods. Under the slab you can use either EPS or XPS (but not polyiso). Again, it's 5" of sub-slab foam minimum whether XPS or EPS to have the lifecycle performance you're looking for, and 2.5" of wall-foam, minimum (any type) to provide sufficient moisture resilience to skip interior side vapor retarders.

    Reclaimers only rarely carry Type-I EPS, since it's a bit fragile due to it's low density, and doesn't come off the roofs in one piece, but if you specify Type-II (1.5lbs nominal density) or denser to a reclaimer they'll usually know what you mean, and it may have some scuffs and dents, but usually won't have gaping holes and large chunks taken off the corners. Since it's often installed in layers on large commercial buildings, it often looks brand new, but the nominal dimensions will sometimes be a bit smaller (eg. 3" foam might only measure 2-3/4" on one end, and 2-15/16 on the other), but unless you're stacking it 3 layers deep it's rarely an issue (completely NOT an issue for the slab foam).

    If the intent is to staple the PEX to the foam rather than wiring it to the reinforcing mesh, making the top inch XPS provides better staple retention than with Type-II EPS.

  4. Andrew_C | | #4

    Make it greener?

    Martin addressed your specific questions. I’ll take a stab at your general question:
    “Any ideas to help me make this a greener house?”

    My $0.02: you are asking good questions and they indicate that you have an attitude that will help you achieve your goals. Keep asking yourself questions.

    More specifically,
    1. I agree with Reid; straight ROI calculations are based on assumptions about the future and rarely capture all the benefits. So it’s worth penciling some things out, but view results with a shaker full of salt. Build a good, healthy, comfortable, durable house that people (that’d be you) will enjoy.
    2. If you are in the process of planning a house, get a GBA membership. I guarantee that that’s the best ROI you’ll have on this project, by an order of magnitude.
    3. Enter “How to Do Everything” into the Search box and look at the collection of articles there.
    4. In-floor radiant heat discussions tend to…generate some heat. It’s a personal decision. Do your reading. If you read a lot of articles and discussions here, I think you’ll find that the general consensus is that hot water radiant floors are not effective in well built houses (i.e., adequately air sealed and insulated). If the floors are hot enough to feel comfortable, the house will overheat. You’ll end up using mini-splits for both heating and your eventual cooling. Again, that’s just my read, I’m pretty sure there’s at least one person who will say that’s a load of wet hay.
    5. If you figure out that you don’t need/want a whole house fan, try to eliminate interior access to the attic completely, and put an exterior access door in a gable end. And while you’re specifying energy heel trusses, ask if they can add supports for a catwalk that would be suspended above your R60 blown cellulose.
    6. If you haven’t read about a Pretty Good House (PGH, see the “How to Do Everything” index of articles), that’s worth your time (IMO), and will indirectly address a lot of your ROI questions.
    7. Every dollar saved in planning is multiplied by a large factor after the building phase is started…or completed. E.g., plan with your builder now for ventilation system installation, especially since you won’t be able to put your utility room in the basement.

    I will be interested to see other people’s response to how to put certain things like air-sealing into a contract/drawing set so that expectations are clear to all parties prior to breaking ground.

    Have fun,

  5. user-2310254 | | #5

    Steve Wolfe. If you are working with a traditional builder, you need to include lots of details in your plan and design specifications. If possible, pick strategies and materials your builder and his/her local subs already know. Where that is not possible, provide enough information to help them meet your expectations with incurring too much of a cost or quality penalty.

    It will be difficult to learn enough about green construction to ensure a problem-free build. To keep the sleepless nights and budget surprises to a minimum, you may want to hire a "green" consultant (perhaps a RESNET consultant) to conduct inspections at key points in the process. Whatever you do, don't pay for work that is not consistent with your design specifications and project details until you are satisfied all errors and omissions have been addressed. Stay focused on the budget and make sure the builder is staying current with all costs.

    Last piece of advice: Be wary of guys (it's usually guys) who say they did so and so because that's the way they've always done so and so. Sometimes a time-honored approach is fine. But sometimes it is a red flag that you should investigate carefully before moving on to the next thing that needs your attention.

  6. user-6258531 | | #6

    Reply to 1. Martin, "good way to seal the fan opening"

    I agree. I like the quiet cool fans with ECM motors. I am considering buying this accessory The skeptic in me requires that I investigate that R 40 claim some more.

    I was wondering if cellulose would have to have some sort of net to prevent it from blowing around with that air flow?

  7. STEPHEN SHEEHY | | #7

    Steve- I'm with Andrew-skip radiant heat and spend the money on a better envelope. Use minisplits and skip the big fan. We used the A/C on several days this summer. It's not essential, but can be nice to have. The house is insulated to about R 45 in the walls and R 70 in the ceiling. The house stayed warm, even though we turned off the heat for good in early April, weeks before our last frost.

    Reclaimed foam will, as Dana said, save a bundle. We ordered some extra but the foam was perfect, just a little dirty. I stuck the excess under one end of the garage slab where my workshop is.

    We built a Pretty Good House. My contractor is a smart guy, but hadn't done anything nearly as energy efficient. It isn't rocket science. Make sure your air barrier is continuous from sill to ceiling. It sounds like you've got the basics figured out. Just make sure to tape all seams on sheathing and wrb. Use a gasket under the mud sill. If you opt for exterior insulation, (and you should unless doing a double stud wall) tape that too. Tape is cheap and some redundancy can't hurt. We ended up at .59ach50.

    Use the money you save on skipping the radiant heat to buy better than U.27 (R 3.7) windows. Better windows means more comfort, as well as energy savings.

    PV is a great idea. Our house is about the size of yours. (Zone 6 Maine). We started keeping good track of energy use and production Oct. 1, 2015. With a 6.6 kw PV array, our all-electric house will use about 9500 kwh over the first year and produce about 8200 kwh. Total energy cost for the year will be about $325 and half of that is the monthly minimum charge from the electric company.

  8. user-6258531 | | #8

    Reply to 2. Reid "Excessive reliance on ROI indicates that you don't value greenness directly, but only value the associated cost savings"

    I will plead partially guilty.

  9. user-6258531 | | #9

    Reply to 3. Dana

    Thanks for the tip on recycled foam board. I'll investigate further. Same with 5" of foam under slab.

    When evaluating R 23 Rock Wool, I assume I would have to use a lower effective R value due to less than perfect installation of batts? I'll add this to the mix. Think I read somewhere it reduces sound transmission better as well.

  10. Expert Member
    Dana Dorsett | | #10

    Seriously, using reclaimed foam saves a lot of green cash up front, and lower energy costs over time. The material cost can be cheaper than batts in R per square foot, but the installation is more labor intensive than batts.

    Any 2x6 16" o.c. studwall will come in at roughly R15 whole-wall, give or take R2, depending on the species of studs, the type of siding. If you stuff it with R19s it'll be close to R13, and even if you filled it with R30-R33 of closed cell polyurethane it won't be more than about R17. Assuming western hemlock framing (about R1.2/inch) and a 25% framing fraction (typical for 16" o.c. framing), half-inch CDX, half-inch wallboard and vinyl siding your looking whole wall performance of about R13.6 if R19s (really R18), whichis about U0.069, whereas with R23 rock wool it would be R16.1 / U0.062. No batt installations are perfect, but with the framing caulked to the sheathing inside every stud bay and some amount of inspection diligence to ensure very few voids, thermal bypasses or compression, real-world performance isn't far off from those numbers. The rough rule of thumb, call it R15.

    So think of the batt wall as R15 (assuming R20 mid-density batts or better), and a 3" polyiso overskin as the second R15, for roughly R30 whole-wall. The R15 skin provides huge moisture resilience to the structural wood by keeping it warm enough to not accumulate wintertime moisture.

    But an R30 wall can buy you a lot more:

    At R30 whole-wall with an R60 attic you may be able to hit Net Zero Energy with heat pumps and a PV array that still fits on the roof if you bump the window performance to U0.24 or so. You might be able to get there with U0.27s though, given that you don't have any west facing glass driving the cooling loads up. Some amount of building simulation using BeOpt would tell you whether that would be desirable or necessary.

    Take a peek at Table 2, p10 of this document:

    Those are all "whole assembly R" numbers, with all thermal bridging factored in.

    Bear in mind that it was when PV efficiency was under 15% efficiency, whereas now 20% isn't a big mark-up, and cold climate ductless heat pump efficiency ratings were HSPF 10-ish rather than this year's HSPF12+. What made reasonable sense for a zone 5 climate way back then (2010) would reasonably apply to a zone 6B climate using current generation heat pumps & PV.

    Using that as a guide U0.24 windows, R60-R65 in the attic, and 3-4" of reclaimed roofing polyiso on the exterior of a batt insulated wall, and your sub-slab R20 would pretty much get you there if paying attention to all the other air sealing and slab edge insulation details, etc.

    I don't know what a reasonable hydronic floor heating design costs fully installed in your area, but in my area it would be north of $20K. In my area 2.5-3 tons of name-brand cold climate ductless comes in under $15K if competitively bid. Eyeballing your floor plan, if you build to the zone 5 recommendations in the above linked documents it's likely that your heat load at Coeur D' Alene's -1F design temperature would be under 20,000 BTU/hr, and comfortably within the output range of 2 tons of ductless/ mini-duct To have sufficient capacity when it hits negative double-digits it's not insane go with 2.5-3 tons, depending on where the load numbers actually fall.

    Shrinking the north facing bedroom/office windows to something like the legal minimum for codes regarding egress would lower the load numbers too, and might be desirable unless you're micro-zoning it with a heat emitter in every room. If you went strictly ductless you'd need about 6 ductless heads to cover every major space and doored off room, which takes about 4 tons of multi-split, which will be a bit oversized for the loads to run super-efficiently, but it's not bad. Last year about this time I was involved with a project on a bigger house at code-min or less R values that eventually went with a pair of 3 zone 2 ton Fujitsu multi-splits (for a design load of about 30,000 BTU/hr) that was overkill, but they insisted on the room-by-room zone control. A few weeks ago I ran a spreadsheet of their power use against heating degree-days, with estimated subtractions for other uses, and it seems to be performing better than I had anticipated, despite excessive cycling rather than modulating during the shoulder seasons. The installed cost on that system was about $15K.

  11. user-6258531 | | #11

    Reply to 4. Andrew

    I have my GBA membership.

    Yes, I knew I was stepping into by mentioning in floor hydronic heat. I've read a lot here and other sites. This might be better for a separate post.

    Great ideas about about catwalk supports and alternative attic access. These are good examples of things that might not cost much if planned for, but almost can't be done after the house if built.

    I break ground in April 2017. I will plan obsessively until next February when a contract to build will lock in the design. Right now it is extremely valuable to get potential ideas to evaluate. Thanks for your ideas and the others who have responded so far.

  12. exeric | | #12

    Everyone has their own orientations and preferences. One has to modify those desires to the climate you live in. It sounds like you do not like to have breezes blowing about from mini-split units. As you've assessed, a hydronic system is less intrusive in that way and opens up more architectural options that may be high on your aesthetic list. However, it is much tougher to design such a hydronic system. It probably isn't a job for a DIYer, even for someone who enjoys doing it. Richard McGrath, who comments a lot here, is someone who knows a lot about such systems and can set you on the right path. If you're willing to go to the extra complication and expense of designing and installing such a system it will work for you. You have your preferences. We all do.

    If you decide to go for a heating only system like that then I like your idea of a whole house fan in your climate. I think many people from the East Coast dismiss them out of hand because they really do not work in humid climates. I think it would work in your climate. The go-to WHF at this forum may not be the best one for your preference. The ones usually recommended have the fan installed at ceiling level so they are kind of loud. If you really don't want to be exposed to that then you should investigate the Quiet Cool fans. They are installed at the end of an insulated duct and are a far remove from ceiling and don't transmit vibrations to the physical structure. A lot of people do not like them as well as the ceiling mounted one because those have a mounted insulated 6" thick damper. However the Quiet Cool ones have a recessed metal can that the insulated duct is attached to. It essentially allows you to install an insulated foam square about 18" x 18" by 4" thick in that recessed can above the ceiling grill. You would install and then remove it one time a year. Not a big deal for the additional silence of this type of WHF.

    I agree that you should concentrate on getting the home air tight and well insulated before you make any decision on how you want to heat or cool the house. The easiest way to seal and insulate your home is by using the ZIP system of insulated wall sheathing, though I don't know the particulars of your climate and how it would work there.

  13. Expert Member
    Dana Dorsett | | #13

    I have nothing against hydronic floor heat (I have some in my own not-so-high-R house) but air source heat pumps may be both cheaper to install, and cheaper to operate.

    If you go the hyrdronic route, at your likely heat loads a condensing tank type hot water heater set up as a combi-system is probably going to work out better than a modulating condensing boiler, and that would also allow you to micro-zone it (if desired) without short cycling the burners. But even a hot water heater based system probably won't come in cheaper than ductless heat pump solutions, unless you use this project as your Hydronic Engineering thesis project, discounting your design and plumbing time.

    Whole house fans are fine in that region, but it doesn't take a lot of fan to manage that in and 1800' high-R house that has the thermal mass of a 4" slab keeping the temperature peaks bounded. The lack of east & west facing windows on this house means that the summertime solar gains will be limited, and can be optimized by the roof overhang design on the south side. The low summertime dew points in the Pacific Northwest (where I have spent many summers- winters too- I'm a WA native :-) ) make night ventilation an effective cooling strategy even in not so high-R houses, with even less thermal mass on the interior to work with. Nearly everbody in eastern WA & the ID panhandle has used night time ventilation cooling, and central air conditioning isn't nearly as common there as it is in some other parts of the country.

    Then again, it doesn't take a lot of mini-split to keep up with the loads during the day, when the PV array is delivering the goods. Eyeballing the floor plan I'd hazard the peak cooling load at the local mid-80s F 1% outside design temp is about 1-ton maybe less. The latent loads are in fact negative (with rare exceptional days)- it's all sensible load. If the whole house fan isn't under thermostat control and is a crummy AC motor drive it wouldn't always be using less overall power than a high SEER mini-split that is allowed to just modulate with the load. If you end up going with a heat pump solution for heating there may not be an energy-use rationale for a whole house fan, but it makes total sense if the heating is gas-fired hydronic.

  14. user-6258531 | | #14

    Reply to 7. Stephen
    Thanks for your thoughts, very impressive energy use on your home. And now that I discovered your blog I know what I'll be doing tonight. I lived in Bangor for the Ice Storm of 1998 so I know why you have back up power.

  15. user-6258531 | | #15

    Reply to 12. Eric
    Thanks for helping to communicate the difference between zone 6 Northeast and zone 6 Inland Northwest. I agree on the Quiet Cool fans, there has to be a way to get a reasonable R Value cover for the vent opening and if I go that route I'll use the high efficiency ECM motor.
    Looked at the Zip site. Wouldn't I still have to put 3" in of these panels just like I would with other rigid foam products to avoid moisture problems?

  16. user-6258531 | | #16

    Reply to 10 and 13 Dana

    Thanks for your thoughtful posts. You obviously know your stuff.

    I'm a bit confused by the effective R values you had in post 10 for various walls, but I understand that if I want to get beyond R 20 I need to use foam.

    Any comments on the idea of 1' Polyiso on the interior of blown fiberglass or cellulose? I understand it doesn't likely get me to R 30 but I'm not obsessed with that goal.

    The whole house fan will be a brushless ECM style motor. Unfortunately the manufacturers don't offer advanced control systems. However it looks like one could use smart home tech like Samsung Smartthings to use indoor and outdoor temperature sensors to develop a control strategy for a whole house fan on the cheap.

    I'm going to reply separately to the hydronic versus heat pump question.

  17. exeric | | #17

    Reply to 15 Steve

    I just went to the ZIP site. I didn't want to commit myself to any advice there. I had heard a news item that Huber was developing a structural sheathing that used thicker insulation than R6. But when I went to their web site just now it only shows the R6. So yeah, that would be a problem in zone 6 and wouldn't work for moisture migration control. If anyone knows more about a coming availability of those higher insulation structural panels from Huber then they should let Steve know. If it's vaporware only then it's probably best to forget the ZIP approach for where you live.

  18. user-6258531 | | #18

    Here are my thoughts on the hydronic heat versus mini split decision.

    My goals are:

    Having a comfortable house is numero uno. I attached what I think are heat zones. These are not negotiable in designing a heating system. I want to a have a warm master bathroom. The bedrooms don't ever have to get above 65. Beth wants the kitchen to be cooler than my office. We are going to have a heated garage, probably keep that at 50 degrees. That is six zones.

    Desire to have low heating costs taking into consideration the expenditure to get there.

    We'd like to have domestic hot water too. This is tied into the heating system decision.

    We want to be comfortable in the summer also. Northern Idaho is on the edge of needing air conditioning but if we don't do mini split/AC then a whole house fan is required.

    Note that is is not a goal to have my little tootsies feel warm when I stand on the floor. I own slippers.

    Design considerations

    Whether I go with R 30 or R 18 walls and only Energy Star windows or better, the rest of the house is going to be to PGH standards. So the heating system load is going to be fairly low. Based on Dana's post and my calculations, it is going to be between 20,000 and 30,000 BTU/hr max.

    Looking at my heating zone diagram, with a mini split system I'll need an 5 or 6 indoor units. I'll also need to put a natural gas fired heater in the garage or a sixth indoor unit. Not sure if you can do that with one outdoor unit or if you need two. All of those units will need to have some type of condensate drain system. With this option I'd add a tankless high efficiency gas fired hot water heater.

    Likewise with a hydronic heating system, I'll need six zones. Lot of variation on how to implement, either using a hot water heater to supply heat or a boiler. I'm really concerned that I can find a system that works well at the low heating loads I anticipate.

    The incremental cost of heat with present Avista utility pricing supplied by either system is

    Heat Pump assuming overall COP of 2.5 the cost of one MMBTU of heat is $12.55

    Hydronic heat assuming 95% efficiency the cost of one MMBTU of heat is $8.12

    I'll assume the cost of indoor unit blowers equals hydronic system pumps to distribute heat.

    What am I not considering?

    I'll make my decision by evaluating the installed cost of these two systems (modified by your comments) and the ongoing cost of operation.

  19. GBA Editor
    Martin Holladay | | #19

    Q. "I had heard a news item that Huber was developing a structural sheathing that used thicker insulation than R6. But when I went to their web site just now it only shows the R6."

    A. Thicker versions are available. Here are two links to documents on the Huber web site that include information on thicker versions of Zip R sheathing.

    Zip System R Sheathing

    Zip System R Sheathing Submittal Form

    And here is a link to a GBA article on the topic: Nailbase Panels for Walls.

  20. Dana1 | | #20

    Based on NEEA field surveys in occupied homes, even the older Mitsubishi FE12s averaged a COP of 2.96 for a monitored fleet of 12 units in Idaho Falls. That unit was rated about HSPF 10 (COP= 2.93) for heating zone 4 (not to be confused with DOE climate zone 4), in HSPF testing by the manufacturer but seemed do that well or better real world conditions, even in cooler locations. Over an even broader number of models and locations, average in-situ performance in Idaho was over 2.8. See Table 9, p30:

    Newer cold climate mini-splits have 15-20% higher HSPF numbers, so you probably won't do worse than 3.0, even with multi-splits rated HSPF 10-11.

    That brings the heating cost estimate down to $10.46/MMBTU.

    Gas is currently trading near all time low pricing with nowhere to go but up, since much of the new gas production is linked to fracking for oil, which is very sensitive to world oil pricing. Drilling rates are down from a few years ago when oil was averaging ~ $100/bbl and fracked wells have an average productive life of about 3 years. In order to be able to pay the financing on the already sunk costs they are pumping them even faster. Bottom line, barring major technology innovations making fracked oil wells more cost effective, the price of natural gas really has nowhere to go but up.

    By contrast, as more zero-marginal cost renewables go on to the grid, the wholesale price of electricity is falling, falling even faster now than the 50 year trend, which has been fairly consistently price deflationary in inflation-adjusted pricing. Wholesale electricity is somewhat sensitive to natural gas pricing, which has been a part of the recent steep declines, but in markets like Texas and parts of the upper midwest wind power has been eating their lunch too, severely blunting the price of peak power (which had been a lifeline for thermal coal and nuclear power.) Wind carried the lion's share of new generation capacity in 2015, followed by natural gas (= upward price pressure on gas) and solar. EIA projections for new generation for 2016 and 2017 are almost entirely zero marginal cost renewables.

    Note: EIA projections on renewables have historically chronically lowballed (often pretty badly) and the numbers prior to 2016 do not include behind the meter solar, only larger scale commercial & utility scale arrays, are counted, ignoring roughly 1/3 of the total solar power additions, which still affects markets.

    If Watts Bar 2 manages to fix their startup issues before the end of the year, nuclear will dominate the non-renewables additions for 2016, after nearly a decade of rapid growth in combined cycle natural gas, which is currently on pause, but which is likely to continue to grow as coal generators retire.

    The levelized cost of wind power already beats combined cycle gas even at fairly low gas pricing, and utility scale solar will too. The net effect on the market over the lifecycle of heating equipment is strongly deflationary- electricity is likely to fall in real price faster in the next decade than the 50 year trends. There will of course be local markets that vary, but electricity pricing can't rise by much without inducing massive load defection by now cheaper site-sourced power from renewables.

  21. user-6258531 | | #21

    Reply to 20. Dana

    My COP estimate was based on a Canadian report, see attached. But that is a 2004 report so perhaps the COP of new pumps is higher at lower temps. This looks a lot like page 16 chart in the report you cited. I'll accept that 3.0 might be the real COP, but note that the report you cite does show the Inland Empire COP at 2.4. But lets not quibble over that.

    I'll be meeting with my builder next week and should be able to get a rough cost estimate for 6 zone installed hydronic heat system. I'm not sure how to estimate a cost for a mini split system that meets my comfort goal. Certainly the 6 zone system you mentioned above and a tankless gas water heater would meet my goals so I'll use that as a starting point.

    I'm totally clueless about how a PGH house is for comfort. I've read the reports of people who only have two mini split indoor units in houses my size. Are all the rooms comfortable? Do they put up with a cold bathroom warmed by the knowledge that they have low utility bills? I don't want to dismiss going the mini split route by using a two compressor six head design that will likely cost as much as hydronic heat if that isn't what it takes to be comfortable.

    I think you are overlooking a big factor in your predictions of lower electricity and higher natural gas prices. That is the power grid. When the wind doesn't blow and the sun doesn't shine, people are still using power. I think the utilities will eventually prevail in lobbying to make subsidized renewable generation "pay their share". How that translates to legislation is beyond me, but it could mean less generous net metering laws and/or reduction of subsidies for renewables.

    My investments in a wood stove and solar panels are my means to have some buffer no matter what energy source pricing does.

  22. user-6258531 | | #22

    Reply to 19. Martin

    Thanks for posting this. Am I correct in thinking because the sheathing is on the outside of the Zip System R sheathing panel that the minimum insulation thickness table for putting rigid foam on the exterior of OSB sheathing does not apply? It would seem in this case the OSB sheathing exterior of the panels would be subject to moisture gain just like a standard 2x6 wall with batt or a double stud wall. But because it is one the outside, it would also have the ability to dry out in warmer weather. Is this correct? I'm in zone 6.

  23. Dana1 | | #23

    The state of the art of air source heat pumps have improved by leaps & bounds since 2004, and the Canadian report was based on modeling of single speed ducted air source heat pumps with HSPF ratings of 6.7-10. Most cold climate single zone ductless units have an HSPF of 12-14 these days, but when optimally sized can beat that in climates like yours.

    A six zone all ductless system runs about $15K in my neighborhood. If you're using primarily mini-duct cassettes it could add another $5K. (I've seen quotes for all ductless systems that size north of $20K, but they didn't get the business.)

    The wind is always blowing (somewhere) and the sun is always shining (somewhere.). The net effect of distributed power sources (any type) is to lower the amount of grid infrastructure required to get the power to the load, and to drastically lower the peak capacity requirements of the grid. Having widely distributed smaller scale generators also reduces the spinnning reserves required too. A 2 megawatt wind turbine can crap out suddenly, but it doesn't bring down the rest of the wind farm, and the biggest point-source failures of PV are the size of an individual inverter, which is pretty small.

    Modeling of weather data the PJM region (mid-Atlantic to Ohio & Indiana) has demonstrated that it takes less storage and other backup to operate that grid with 99.9% intermittent renewables than if it were "only" 80% renewables, and that's without additional transmission grid cost.. Large central power plant model imparts additional cost if it's something slow ramping like nukes & thermal coal even at 25% renewables, since at low grid load the power has to be curtailed, imposing the cost of something else to cover the ramps. In Texas it was cost effective to build large transmission lines from the wind zones in the west to the markets in the east when wind capacity factors were only 25% in the lighter wind east, but in the past 10 years capacity factors for newer technology would be north of 35% , even in eastern Texas (and pushing north of 45% on the windswept plains.) Even with the cost of the transmission infracture that they actually built, the retail cost of power has fallen, largely due to what wind has done to peak and average wholesale pricing, putting a lot of thermal coal out of business. But now that solar has crossed to even lower price point, the ERCOT grid operator is anticipating that SOLAR will be replacing most of the retiring coal fired generation in Texas:

    The tools for managing the change won't be in the form of increased grid capacity upgrades, and is more likely to be market reform that encourages behind-the-meter storage for large commercial customers, and better utilization of the remaining gas fired generation, either of which would be cheaper for the ratepayers than massive grid infrastructure upgrades.

  24. GBA Editor
    Martin Holladay | | #24

    Q. "Am I correct in thinking because the sheathing is on the outside of the Zip System R sheathing panel that the minimum insulation thickness table for putting rigid foam on the exterior of OSB sheathing does not apply?"

    A. Not in my opinion. With Zip R sheathing, the interior surface of the polyiso layer becomes the first condensing surface. You certainly don't want moisture to condense there, because it will run down the face of the polyiso and puddle on the bottom plate, which can lead to mold or rot.

  25. exeric | | #25

    Steve, in your zone 6 the insulation requirement for a PGH (which I'm assuming you want) amount to either a double stud wall or foam panels on the outside of the framing walls. Either way it's kind of complicated in my view. Bear in mind I live in zone 3 so maybe to builders in zone 6 either one isn't complicated. To me it is.

    The ZIP system is much simpler. Probably the biggest simplification is that it doesn't require extensive planning for door or window bucks. Also, if you follow Huber's procedures for flashing it appears to be almost fool (fuel?) proof and provides a very tight wall structure. Admittedly it will require outie windows. If you end up deciding to go that route for the walls you might be breaking new ground. I do not know of anyone else here that has used the R-12 version, which is what zone 6 would require. That's something to be aware of as sometimes there are teething problems for any new product, sometimes involving just acquiring that new product.

  26. exeric | | #26

    I should add that siding attachment with a ZIP panel uses the outer OSB as the attachment point. Cumulatively all those advantages really add up. But you WILL be paying more for the ZIP panels which will presumably be recouped in reduced time and labor costs. Use that as a bargaining point for any prospective builder. Don't let them con you into just adding the increased cost of the ZIP panels without the concomitant reduction in other labor and material costs. In other words, it might be good to get a total cost estimate for standard construction techniques before you suggesting ZIP panels. Then if they try to raise the total cost you then have a bargaining point by making them informed on all the other reductions in cost they will have using that method. It's always best to expect that if a procedure is out of a builders comfort zone and involves a more costly component that they will try to ding you for it even though the builder is really getting a super deal out it. Don't be the rube to a builder who's trying to take advantage of you for their own ignorance. Happens all the time.

  27. user-6258531 | | #27

    Reply to 25 and 27


    I would say my goal is to approach a PGH but I may not get there in the walls. From what little I know, that seems to be the piece that gets more complicated when you go for PGH. My initial post with guestimated cost for adding 2.5" of XPS must have been close or I suspect I'd have gotten some push back. It seems like achieving PGH in under slab insulation, ceiling insulation, and windows are primarily material cost decisions with little impact on building labor costs. Reducing air infiltration is likely more of an increase in labor, but I am committed to having a tightly sealed house. My use of ROI is that I suspect I may have to choose between better walls or some level of better windows. Since I don't have unlimited money, I don't know any other way to make the decisions.

    My builder does not have experience with adding rigid foam to the outside of the house, but he appears to be open to the idea. I'll know more after we have a design meeting next week.

    I would think most builders in zone 6 who plan to be in business for another 10+ years realize that they eventually are going to learn how to go beyond 2x6 with fiberglass batt. I like your suggestion of starting with discussing cost of OSB/rigid foam/window boxes/furring first before getting into possible ways to reduce total cost such as Zip panels.

    I'm pretty sure somewhere on this site I've seen some disagreement with Martin's opinion regarding using R 12 Zip or other panels that have the OSB on the exterior in Zone 6. But I'll have to be convinced it would be OK before considering them.

  28. user-2890856 | | #28

    Steve ,

    Nice plan and house . The only way to zone the way you want and insure those various temps is with a water based solution . Does not have to be so expensive either as long as you don't go through the regular channels that have been used in the past . I just got reports from a homeowner in Michigan whose average gas bill for year one is 56.00 per month with a slab on grade PGH (ICF) with radiant .

    Others have stated that you should discard the 2004 findings about heat pumps and I agree . However , there is a more recent report on their heating performance that is also not so flattering . I'll try to find it amongst the documents I have stored ( cluttered machine) and post it .

  29. user-6184358 | | #29

    ZIP Sheathing Structural Issues - Hi,
    The ZIP insulated sheathing has certain penalties when used as a structural sheathing to brace the builiding under seismic loads. Looking at the ICC report it lists the shear nailing schedule and allowable loading. In Section 4.5 &4.6 of the ICC report it indicates the design criteria. It lists the Response Modification Factor (R) of R=2.0 - not the insulation value. Shear panels usually can use an (R) of 6.5. This means the building will need to be designed for a higher force, due to the weaker shear panels. From exapmle in Sand Point ID Seismic zone C it would take the seismic lateral force the building needs to resist from about 5% of the building weight to about 17% of the building weight , so more shear walls. Very similar to installing shear panels over drywall to get a fire rating, it has a lower shear vaule. The nails thru the foam into the studs makes for a weaker connection than if the shear panel was directly against the studs. I think this would then add significant cost to a building and is not really a direct comparison to plywood with exterior foam due to the different structural properties of the ZIP insulated Sheathing VS ply & exterior foam.

  30. exeric | | #30

    Reply to Tim.
    Good point. I hadn't thought of that. But wouldn't it just mean that one has to determine the predicted seismic loads and expected wind loads in the area one Is building? For instance, I'm pretty sure their R-6 (insulation) panels and lower meet the requirements for typical loads in most areas. It seems like it may just end up being a process of pre-qualifying the high insulation panels for the loads expected in the area one is building.

    It certainly seems like it would be deceptive advertising when using the R-9 and R-12 panels if ALL locations required additional seismic beefing up (other than a different nailing schedule) to be able to use them as intended. It would kind of negate most of the logic of using them. Stranger things have happened though.

  31. Reid Baldwin | | #31


    Have you decided what type of cladding you will use - brick, vinyl siding, hardie board, stucco, etc.? That influences whether having the sheathing on the outside is really an advantage or not. For some types of cladding, the rainscreen formed by furring over exterior foam is an advantage.

    My builder was in a similar position to your builder. He had used exterior foam only once before and it was an awful experience. They hadn't worked out many of the details sufficiently in advance. They ended up standing around the job site, while paying a crew of idle workers, trying to figure things out on the fly. For my house, we agreed on those details in advance. It went smoothly and added less cost than the builder expected. The only complaint I heard from the crew was that installing the foam and taping seems was tedious and boring relative to putting up the walls, but it was not difficult for them.

  32. JC72 | | #32

    +1 for ZIP-R. Exterior cladding attachment is much easier for a typical builder using ZIP-R. I admit that I'm a fanboy for the product and had it spec'd for a build that never happened.

    The big con for ZIP-R is price and the additional bracing needed for your required foam thickness. Sure you'll recoup some of that cost via reduced labor but IMO the biggest benefits are #1 piece of mind knowing that it's not something that's entirely foreign to the builder and his crew, #2 It's a clean look (no house wrap flapping in the wind or getting torn, no worries about whether the house wrap was flashed correctly, or whether the builder installed the windows prior to installing the house wrap, less waste).

    I live in climate zone 3 and over the past 9 months or so I've seen ZIP sheathing go up on apartment buildings as well as single family homes. I haven't seen production builders use it yet, but their business model relies on cheap labor provided by subs for framing.

  33. user-6258531 | | #33

    Reply to Chris, Reid, Tim, Eric,

    I am pretty early in planning, just meeting with builder and draftsman Thursday to look at preliminary elevation drawings.

    I think we will likely use the Hardiplank panels and battens to get that board and batten look. I was wondering how vertical furring would work with that and if I would still need furring even with Zip panels? It is on my list to discuss with my builder.

    My thought is that I have the winter to constantly bring up the details of adding exterior foam if we decide to go that route. With all the good info on this site I think I can educate him over the winter on the details.

  34. Expert Member
    Dana Dorsett | | #34

    It's true that ZIP-R has a negligible learning curve to it compared to 2.5- 3" exterior foam, and R12 ZIP-R would still have adequate dew point control at the foam/fiber insulation boundary for this climate, even after derating of the polyiso for temperature. (That is due to the additional ~R0.5 of the exterior side OSB.) From a labeled-R point of view it has plenty of margin. Derated for climate & temperature it has less, but still some.

    ZIP-R can't dry toward the exterior due the low permance facers and the wall stackup has to be set up to dry toward the interior. And while the dew point margin is adequate with R12 ZIP R, it isn't huge. The eternally anxious could install a 2-mil nylon (eg Certainteed MemBrain) variable permeance vapor retarder on the interior, which may be necessary to appease inspectors in locations where 4-6-mil polyethylene is the norm. Thin nylon is fairly vapor tight when the proximate air inside the cavity has a relative humidity less than ~35% (which it will be all winter unless you are actively humdifying the house to some ridiculously high level), it performs in the Class-II vapor retardency range, but it becomes more vapor open than interior latex paint if the moisture in the cavity ever reaches mold-growth potential, which allows it to dry toware the interior. Certainteed MemBrain is fairly widely available now, and cheaper than the imported "smart" vapor retarders even when sourced at retail through the big box store chains. At box store pricing and small rolls it's a 15 cent per square foot cost adder, but substantially cheaper through distributors.

  35. user-6184358 | | #35

    If you want the ZIP insulated sheathing, the best way to go may be to install 1/2" shear panel on the shear walls then over lay with the ZIP insulated in various thicknesses to make everything flush. They have the requirements clearly in the ICC Report, every thing has details that need to be accounted for. New system new details.
    They also specify that all panel edges must have blocking behind them. They don't seem to do shear wall blocking from what I have seen on This Old House.
    New cool stuff has new requirements.
    Idaho is pretty dry I am not sure you need a rain screen. Also if you need to build for wildland fire resistance a rain screen may not be allowed.

  36. exeric | | #36

    Here is the applicable report submitted by Huber and approved by the ICC:

    I don't understand all the jargon tossed about so it is definitely confusing to me. But I gather all R-panels can be used in seismic zones A,B, and C in residential construction. It's not clear to me what zone northern Idaho is. There does not seems to be any discrimination between any of the R-panels in regard to seismic regions. Seems kind of odd. Maybe someone with more background can fill us in on how to apply the information in that document. And go easy on the jargon. Use of excessive jargon to individuals who are trying to learn is not needed here.

  37. exeric | | #37

    Here's something I just located.

    It's a slightly dated map of the seismic design criteria for the USA. From my admittedly amateur status it "looks" like northern Idaho is squarely in either zone B or C. If I'm understanding what I'm looking at, no guarantees, then it looks like according to the ESR-3373 no modifications are necessary with the use of ANY Huber R-panel in northern Idaho. Just as long as you are not building a condo in zone C. I'm open to being corrected as I'm learning on the fly, just like most people.

  38. SwitchgrassFarmer | | #38

    Re: "Hardiplank panels and battens to get that board and batten look. I was wondering how vertical furring would work with that..."

    We have Hardie panel and battens on our house. It was a surprising amount of work by the time you seal all the edges, use appropriate trim boards and flashing to keep the Hardie away from ground, roof, and deck areas that may remain wet, and use the right expansion trim between upper and lower panel sections.

    With regard to the question on furring, we ended up making a SketchUp model for all the faces of the house in order to get that placed so that the battens covered all the nail holes, and so the battens still lined up right with windows and doors. That way we were able to place our Cor-A-Vent strips spot on.

    As to the need for rain screen or not, Hardie's residential side doesn't seem to mandate such use, but they strongly imply it's what is necessary: "For single-family construction, James Hardie recommends installing a 90% efficient drainage plane or a 3/8 inch air gap (i.e. rainscreen) between flat-to-wall siding and the water-resistive barrier as a best practice."

  39. exeric | | #39

    Steve, after thinking about all the pros and cons individuals have thrown out about wall insulation the only negatives that have stuck about using ZIP R-12 is that it is more expensive initially but probably not in the total cost of the build when including time, labor, and bill of materials. That and the fact that it is new.

    It meets seismic code for where you're building with no other seismic modification unless you have wind speed limitations I don't know about. That would seem far fetched. Basically they've engineered it so that the increased nailing schedule for R-12 meet the same shear requirements of the lower R panels. Basically your builder (and you also) have no idea just how much time and effort will be reduced in having a nailable and air sealable surface on the outside will provide.

    Given the two wall designs and one builder of average conscientiousness the ZIP R12 wall will beat the foam only exterior with window and door bucks hands down. There is just simply a lot more things to go wrong in the conventional type foam wall. If you have a builder who isn't comfortable with green building it is more important to go to the ZIP system. Your builder just might not be aware of what he is up against in the difference between the two types of build if he is a first timer for both. If he was already comfortable with one type that would be another issue altogether and there might not be an advantage of one type of build over the other.

  40. user-6258531 | | #40

    Reply to 34 to 39

    Thanks for all the good additional information. I feel a lot more informed for my builder meeting on Thursday.

    Andrew, your post is very helpful in regards to Hardi board and batten, although it also gives me more to worry about. But better now than after it is built.

    Dana, thanks for the confirmation on the adequacy of Zip R 12 in my zone.

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