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Insulation recommendations for Clime Zone 3, Spartanburg, SC

Eggschillin | Posted in General Questions on

Hello.  Building a basement+ first floor+second floor new home.  Using Superior walls for basement.  These already have insulation in them and the space will be conditioned (shop space).  Foot print is 32′ wide x 75′ long… floors stacked on top of one another.  Roof pitch is steep 14/12. Metal roof.  

No HVAC systems will be in attic. Mechanical closet on second floor will handle HVAC]

 A linear vent free fireplace on 1st floor will heat home into in winters. 

What would be a cost effective solution for insulating this home?

Thinking blown attic and spray first and second floor walls with a closed cell foam.  Is this overkill in my area?  

Thanks for your advice.


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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Michael.

    For the attic floor, the International Residential Code calls for R-38 in your area I believe. Blown in cellulose is a great option for cost-effective and environmentally-friendly attic insulation. That's approximately 12 inches to allow for settling. Most of an open attic will allow for that depth, but if the roof framing or trusses are not designed right, it can be impossible to get that depth over the top plates. If it's not too late, look into raised-heel or energy-heel trusses (same thing, different names).

    As far as the walls go, in Climate Zones 3, the minimum requirement for cavity insulation is R-20, or you can satisfy the requirement by installing R-13 cavity insulation plus R-5 continuous insulation. I like the latter option because it creates durable assembly and you can get there with a combination of cellulose and rigid foam or mineral wool exterior insulation.

    Closed cell spray foam is neither cost-effective for cavity insulation or environmentally friendly. If you choose to use exterior continuous insulation, avoid XPS. EPS, mineral wool, or reclaimed polyiso are much more climate-friendly choices.

    You can always exceed these code minimums and keep in mind that more important than insulation is air seal. You should plan for a continuous air barrier and test the air barrier before it is too late to find and seal leaks.

    You may find these articles helpful:
    Walls that Work
    How to Insulate an Attic Floor
    Blower Door Testing
    Blower-Door-Directed Air Sealing

  2. Steve Knapp CZ 3A Georgia | | #2

    Hi Michael,

    Brian has given you a good insulation strategy, but I am wondering about that fireplace. Vent-free fireplaces are a bad idea, especially in a relatively tight home. Combustion of any sort reduces indoor air quality and really should be avoided. (See for why.)

    As part of your build process, you will want to have an independent engineer determine your HVAC requirements and spec equipment requirements. (See for more information.) It's also important to think ahead about how you will ensure sufficient fresh air changes. (See for more on this ongoing argument.)

    New construction tends to be a lot less tolerant of missteps in the construction process. Fixing mistakes down the road can be extremely expensive.

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