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Pretty good house North Carolina

Trevinmm | Posted in Energy Efficiency and Durability on

hello green building community! Dedicated reader here for a few years now never  posted before. I am building a new construction house in North Carolina climate zone 4. I am looking to build to pretty good house level or at least better than code. This will not be a forever house so I am looking to keep the upgrades to ones that have decent ability to recuperate their cost in a 10 year period. Or have significant health benefits. It is a 36×36 square with conditioned living space above. I am currently planing on slab on grade 2×4 construction (that is standard around here) with 2” exterior insulation on walls and roof. I will try to attach a picture of my floor plan, the back of the house faces south. I am planing on using a ERV with probably a ducted mini split in the conditioned attic. the garage will be separated by a breezeway. Any advice on cost effective upgrades would be greatly appreciated or any design flaws y’all notice. Things I have not decided on are interior insulation. Although I like blown insulation i might go with bats for cost and ease of construction. I do not know on windows yet I do not plan on buying the nicest ones at there appears to be almost no payback on a significant cost. Probably just go fixed where I can and mid grade casement windows where needed.  I plan on zip for walls and roof with overhangs added with the exterior foam 
Any advise would be great!

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Replies

  1. Expert Member
    AKOS TOTH | | #1

    Your wall works out to around R21 whole assembly. That is definitely a decent wall for your milder climate. Just make sure you have a builder that can work with it. Until it become mandatory here, it was silly expensive to get exterior foam installed.

    A 2x6 24OC wall with mineral wool/high density FG batts will get you pretty close to that R value (R18) and would be much closer to "standard" construction. If you want even more, bumping it up to 2x8 would give you an R24 wall.

    I would check your roof exterior/interior ratio with the values shown here:
    https://www.buildingscience.com/documents/building-science-insights/bsi-100-hybrid-assemblies
    The 2" you are proposing seems insufficient.

    The ducted mini split is definitely a good way to go. I would go with one of the mid-static units since you have long runs. Check that you have a local installer that can work with you, sometimes ducted mini splits costs here are many many times material cost. It might be cheaper to go with a standard high efficiency heat pump/furnace as a Greenspeed.

    For windows, getting right coating and SHGC on the windows based on the orientation is worth it.

    Make sure you have a solid continuous air barrier in your building. Getting that right is the most important detail for energy efficiency.

    1. Trevinmm | | #2

      Thank you! I plan on doing an owner build and doing the exterior foam myself. I run a Comercial masonry crew that us used to working with Rigid insulation. So that’s actually one if the reasons i am planing on going that route. The air barrier will be zip sheathing walls and roof so I will have total control of it before insulating And not be relying on all the other trades to create airtight drywall. This approach will probably cost more but simplify it. Hopefully i can find some recycled rigid foam and not come out that much higher than blown cellulose in a vented Attic. Thank you for the link i may need to bump that up to 4 inches on the roof

      1. Expert Member
        AKOS TOTH | | #5

        One area you can save a bit on roof insulation is by complying with code on U factor basis instead of center of cavity. I think in your area this would mean an R38 whole roof assembly. There is very little energy saved by going up to R49 and with exterior rigid insulation and you add a fair bit of extra cost to get there.

        This could reduce your roof insulation to around 2.5" of exterior polyiso with R24 batts on the inside.

  2. walta100 | | #3

    If the plan is to be in a home less than 15 years all the stuff we talk about on this site make no financial sense. Nothing you cannot see adds any resale value. 99% of people could not care less about insulation, air sealing, window coating and EVR. In fact if you select an odd HVAC system like a mini split you will scare away some buyers.

    Windows are a huge budget item when building but most buyers never even think to open a window before they have bought the house.

    Take a look at a few of the subdivision builders their focus is 100% on resale value VS cost.

    In my opinion the amount of stress you put yourselves under making the thousands of choices in building a custom house is not worth living thru unless you are staying forever.

    Walta

    1. Expert Member
      Michael Maines | | #4

      Most Pretty Good House improvements pay for themselves within 5-10 years. That's kind of the whole point--keep making improvements until they stop making financial sense. Some things are hard to quantify, such as comfort and environmental responsibility. Most people don't understand enough about these things to care. Once they understand, they often care. Sometimes they don't.

      I'm not sure where you are but in New England, ductless mini splits are anything but odd--they are very common.

      1. walta100 | | #7

        “Most Pretty Good House improvements pay for themselves within 5-10 years.”

        Michael I think you would have a hard time finding numbers to support a 10 year pay back above today’s model code.

        If we assume attic insulation is the most likely option to have a pay back. Let’s look at this set of numbers everyone’s numbers will be different.

        Given
        1 Code required R38 cost $/sqf = .47 (National average cost from BEopt)
        2 R 60 cost $/sqf = 1.07 (National average cost from BEopt)
        3 House size 2500 sqf (wild guess)
        4 Heat Natural gas at 1.5 per therm 96% furnace. (Not uncommon)
        5 HDD =3000 (about right for NC)

        Equals a 10 year savings of $433.00 at a cost of $825.00 a negative ROI of 50%

        Please do not get me wrong , I love this stuff but we all need to admit today’s model codes are quite good and going beyond them is likely to have a very long payback time. Yes I understand not every place is enforcing today’s model code.

        If you decide to do this as practice building your dream house in a few years it could be money well spent as you will learn a lot.

        I will say it again building a house was the most stress full time in my long marriage and I would not but myself thru it unless I planned to stay in the house for a very long time.

        Walt

        1. user-723121 | | #8

          What about homes not on the natural gas grid? If you are heating with oil, propane or electricity the ROI is much different. Cheap natural gas over the years has gone a long way in holding back energy efficient new construction. Money spent on extra air sealing measures regardless of the fuel type will likely show a positive ROI, especially in a cold climate.

          What is the long term value of unburned fossil fuels? As I am fond of saying, "when the oil runs out we will all be the same".

  3. Trevinmm | | #6

    Yes I know the ROI on efficiency upgrades is not great. I am fortunate enough to be able to budget an extra 10k into a 200,000 house for upgrades I got a quote on 1.75 inch insulation enough to do the walls with one layer and the roof in 2 layers for 2900 and would need 1,400 in plywood/2x4/ screws to apply it. I am budgeting 4K for an erv but have not gotten quotes on that yet and it should eliminate 3 bath fans so there is some recouped cost there. I am not counting the zip as an upgrade as it is not much more than plywood with a house wrap. Track home builders have started using it around here. So There is not much left for windows. I do want to build a house that I would be comfortable raising a family in for the rest of my life but not one that I felt stuck in because I had so much money in it I could not sell it. I am not counting labor cost on anything I install either this is fun to me and probably still cheaper than golf

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