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I am building a new home in nw Indiana that will be spray foamed through out.

lowell63 | Posted in Energy Efficiency and Durability on

1800sq ft ranch-2 inches eps under slab in basement. 2 inches closed cell on basement walls 3 inches in rim joists 2 by 6 walls filled with open cell on above grade. 3 inches of open cell covered with 10 inches of cellulouse in attic. We have a catheidral ceiling in the great room that will be 2 by 8 filled with open cell. Vinyl siding on the whole house with anderson 400 windowes. This is our proposed home Wonderihg about moisture and heating system.

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  1. user-2890856 | | #1

    What were you thinking of ? What type of fuel is your preference ?

  2. lowell63 | | #2

    I am retired and am trying to control utility costs for the future. We are in an area that has no natural gas so we are going to have to use propane or electricity. Have no experience with pv so have not given it much thought but was thinking of putting radiant heat in the basement which is a walk out, untill I read Martin Holidays post. Just trying to build a comfortable home.

  3. iLikeDirt | | #3

    I see a couple of problems. First of all, your cathedral ceiling is nowhere near code minimum (R-49). 8" of OC foam between 2x8s is barely R-30 when you take into account thermal bridging of the 2x8s. You could improve this assembly by adding enough rigid foam over the roof decking to reach R-49, which will also keep the roof deck warmer and drier.

    Spray foam between your stud cavities is a waste of money because of the studs' thermal bridging. Filling those cavities with dense-packed cellulose instead will be much cheaper and offer similar performance. And then you can apply exterior insulation outboard of the sheathing to protect it from condensation. You could even "downgrade" to 2x4 construction and use the savings to buy more exterior insulation, which will result in less heat loss and lower ongoing costs.

    If you're planning to use closed cell spray foam insulation on the interior of your basement walls, you'll need to cover it with drywall or another ignition barrier. All of that sounds very expensive. You can save money and time by using Dow Thermax polyiso rigid foam boards, which does not need an ignition barrier. Or you could use poured or pre-cast concrete sandwich panels for your basement walls that have rigid insulation in the middle of the wall instead. Might be the same cost as wall + CC foam + drywall.

  4. iLikeDirt | | #4

    As for heating and cooling, it's hard to beat a mini-split heat pump or two for a well-insulated house like the one you're going to be building. You'll have to price out solar PV to see if it makes sense given your finances and expected residency period. But I'd avoid propane. Its price is high and volatile. Not at all what you want on a fixed income.

    Also, Anderson windows should be fine, but I think they're a bit pricey for what you get. You might be able to get a better deal if you shop around a bit.

  5. lowell63 | | #5

    Thank you Nathaniel I have thought of using closed cell in the cathedral ceiling to get more r value and stop the moisture. the basement is going to be framed out so the only addition will be my dry walling it. will the walls be thick enough that diffusion will not be a problem on the main floor?What about moisture getting behind foam panels in the basement?

  6. user-2890856 | | #6

    Martin's post , the one I believe you are referring to specifically deals with radiant floors and furthermore slabs . Without offending our host I will say that much of the theory is flawed and the conclusions reached were because the people who designed and / or installed these systems were not well trained in the science of how radiant works , especially in the types of houses being discussed here at GBA . That being said , floors are not always the best place for radiant and embedded can be more difficult to control even for the best designers .
    Depending on budget , there are many ways to heat and cool this home , not all of them involve air . If radiant was indeed dead , manufacturers would not be developing and offering equipment with the newest control which senses MRT at the walls and windows . there is an awful lot of R&D going on right now in an attempt to mimic what radiant systems have done for years . You can use a heat pump for radiant heating and cooling and configure your DOAS to handle latent , you will need that anyway .
    R value has much less impact on load than does ACH , air sealing is your most important detail . I would also shop other manufacturers as Nathaniel suggests . There are better windows than Andersen at similar price points .

  7. Dana1 | | #7

    A few comments:

    Open cell foam in the 2x6 walls is about the same R-value as blown cellulose, but is less protective than cellulose since it doesn't politely share the moisture burden. The cost could fall either way, depending on how hungry the insulation contractors are in your neighborhood. If cellulose, specify "borate only, sulfate-free" material only.

    Without at least R7.5 of continuous insulation over the exterior of the sheathing the assembly would need an interior side vapor retarder of 1 perm or less. Polylethylene sheeting can work, but it's extremely low vapor permeance (~0.05 perms) makes it unforgiving, since it blocks all drying toward the interior.

    A 2x6 wall with either cellulose or open cell foam is a code-minimum assembly, not a high performance assembly, but if you make it super air-tight (don't forget to caulk under the bottom plate of the studs, and between the top plates) performance isn't terrible. After factoring in the thermal bridging and the R value of the wallboard/sheathing/siding the "whole assembly-R" will be about R13.5 at a 25% framing fraction ( typical for 16" o.c. construction), R14+ for 24" o.c. stud spacing, and R15 if you use advanced framing techniques and limit the number of corners (which have higher thermal bridging.)

    A better wall at the same wall thickness would be 2x4 16" o.c. with cellulose or o.c. foam, with an inch of polyiso exterior to the sheathing, with another inch of EPS to the exterior of that (stagger the seams by a foot, and tape the seams of both layers for better air tightness). The dual foam type is necessary in zone 5 due to the derating factors of polyiso if it gets too cold. The EPS increases in performance at lower temp, and the 1" + 1" dual foam stackup performs at R10 or better over wide temperature range. Adding in the insulated studwall, and the R value of the siding/sheathing/gypsum the whole-assembly performance is R20, on the order of ~30% higher performance than a code min assembly. This assembly has huge dew point margin at the sheathing, and the interior can/should be left relatively vapor open- nothing more vapor tight than interior latex paint (3-5 perms.) The exterior foam (especially foil faced polyiso) is fairly vapor retardent, but the wall will be pretty resilient to moisture as long as it can dry toward the interior.

    Using the high R/inch closed cell foam between rafters or studs is a waste of good foam, due to the R1.2 per inch of the framing fraction. If you did the 2x6 wall with cc foam it would only raise the whole-wall performance by about R2, not more. Save the the high-R/inch foam budget for the exterior, where it thermally breaks the framing fraction as well, and put the cheap stuff between the studs.

    Furthermore, the HFC245fa blowing agent has a global warming potential of about 1000x CO2 (compared to 7x CO2 for the pentane used in EPS and polyiso.) Hitting R49 with cc foam at the roof would be both expensive (~$8 per square foot!), and it would be too vapor tight for the roof deck to dry at reasonable rates toward the interior.

    In the basement you can get a higher performance wall than 2" of cc foam with 1" of EPS trapped to the concrete wall with a 24" o.c. 2x4 studwall insulated with R13-R15 UNFACED batts. Since the studwall is not structural it only needs a single top plate, which minimizes thermal bridging. With R15 rock wool that assembly comes in at about R15, which is R3 better than 2" of cc foam. At the band joist & foundation sill it's fine to shoot an inch or two of cc foam as a vapor retarder and non-wicking condensing surface, that also air-seals the foundation sill & band joist to the concrete (and your interior side EPS), then put R15 rock wool on the interior side of the foam. That also ends up in the R20 or better range or better at the band joist after thermal bridging.

    Moisture getting between the concrete & foam is not a problem- both the concrete & foam are highly moisture tolerant. Moisture getting into the STUDWALL would be a problem, which is why you go with unfaced batts, with no vapor retarders, so that it dries readily toward the interior. With only 1" of Type-II EPS (1.5.lbs per cubic foot nominal density) the vapor permeance of the foam is no more than 3 perms. But the above grade section would still have minor condensation events at the foam/fiber interface during cold weather, but since neither the foam nor the rock wool store moisture, and the rest of the entrained air in the cavity is below grade, it doesn't accumulate significant moisture during the winters. But if you have the budget for 2" of EPS (about 75 cents per square foot- which is cheaper than 1" of closed cell foam), even those non-accumulating condensation events drop to near-zero, and the vapor redardency drops to 1.5 perms or less, (almost a class-II vapor retarder.)

    For the cathedralized ceilings, use only 2" of closed cell foam (R12) with R23 rock wool on the interior side of the foam. The 2" of CLOSED cell comes in at about 0.5-0.7 perms, whcih is a class-II vapor retarder, and highly protective of interior side moisture drives, and is sufficient for dew-point control at the foam/fiber boundary with R23 rock wool. The center cavity R is only R35-ish with that stackup, well below code min. But if you put 1" of polyiso + 1" of EPS above the roof deck held in place with a non-structural nailer deck of 1/2" OSB or plywood through screwed to the rafters 16" o.c. you'll be pretty close to R49 center-cavity, but it would slightly outperform an R49 code-min between joists due to the R10 thermal break over the rafters.

    For open attic spaces with insulation at the attic floor it's much cheaper to just blow low-density cellulose to about 16" initial depth, which will run about R50 after it settles an inch or two over time. There's little point to using open cell foam on an attic floor- there are cheaper ways to air seal using much less foam. But at least open cell foam is blown with water, not HFC245fa, and it's only about 1/3 the total amount of polymer as closed cell foam per unit-R. But it's about 4x the cost of open-blown cellulose per unit R.

    Until you run a room-by-room heat load calculation on the place it's impossible to know what will work for a heating system. Mini-splits are highly efficient, but not exactly a great fit for a code-min house (or even an R20 whole-wall type of house) in a zone 5 climate unless it's a small house with a very open floor plan. If you build to R35+ whole-wall and go with windows that are U0.2 or less it can be a great solution, but it doesn't sound like that's what you're building.

    To decrease the heat load without increasing the R-values or lowering the U-factors of the windows keep the number of corners of the house to no more than six (an L-topology), and avoid bump-outs & dormers like the plague. Limit the size of the windows, particularly to those of less-used rooms to the min-legal level or whatever it needs for daylighting. On the south side it's OK to go a bit bigger, provided you have sufficient roof ovehang to shade them from midsummer mid-day sun. To avoid high peak cooling loads reduce the west facing windows to ZERO square feet, since it's impossible to adequately shade west facing windows with overhangs, and the solar gains come at the end of the day when the outdoor air & roof temps are still pretty high.

    With any new construction in 2015 it's prudent to think about orienting the roof lines to maximize the sunshine available for photovoltaic solar. Solar used to be expensive, but it's already well below the cost of retail grid power in most of the northeast on a lifecycle basis, and will be cheaper than residential retail power everywhere in the lower 48 of the US by 2025 (maybe even by 2020). The long term 30-40 year "learning curve" of PV solar is that it's price drops about 25% every time the accumulated installed base doubles. In the past 5-6 years the learning rate has been more like 35%, and the doubling rate is less than 2 years. It'll be the cheapest power of any type by 2030.

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