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IRC Energy Requirements Applicability to Accessory Structures

Patrick_OSullivan | Posted in General Questions on

I’m in the early stages of designing a modest shed/shop/sometimes garage space. The main purpose of the space would be to store tools, equipment (e.g. snowblower), bikes, and seasonal outdoor items. The space would never be furnished, never used as an ADU or in any other way “habitable” (local zoning does not allow it). However, I do plan on conditioning it modestly to keep tools in good shape and make it comfortable for any shop activities.

Because the building will be conditioned, I’m considering a frost protected shallow foundation as the requirements in climate zone 4a (NJ) are very modest: 12″ footing depth and only need a relatively small amount of vertical insulation on the footing to keep everything happy.

What I’m trying to “figure out” (and will ultimately ask the local code official about) is what is the letter of the law is with regards to IRC energy requirements and such structures. My initial reading makes me think that because such a building would be conditioned, it falls under the full gamut of the energy requirements, which now in CZ 4a would require exterior wall insulation, and an R-60 ceiling. I’m all for these requirements in a dwelling (maybe not the R-60 ceiling…), but I think they’re a bit ridiculous for an outbuilding.

The irony is if this was built as an unconditioned garage, I could avoid insulation altogether and then come back later and put in a mini-split anyway. However, being unconditioned would not allow for as simple of a FPSF.

Ideally, I would build this simple 24′ x 24′ building with something like fluffy insulated 2 x 6 walls and R-38ish ceiling as there is no way I’ll ever get payback for the increased costs of exterior insulation and R-60 ceiling insulation for a minimally conditioned space.

Any thoughts or experiences on similar buildings?

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  1. Optimal | | #1

    This is not advice, since I am not a registered building inspector, but just a possible consideration for you to implement. This would be a possible hybrid partial solution. You may consider creating a portion of the 24x24 foot area and creating another "room" that may be smaller and has a workbench and other things where you spend most of your time. Likely your ceiling of the 24x24 building has high ceilings at the mid point and you could use minimal power to heat, cool, and add extra insulation to for efficiency. This new extra room could just be 6.5 to 7 foot tall (check code), and built with a ceiling rated for loads required for storage. You end up with a highly insulated workspace that can have reversible blower fans to help heat or cool the rest of the 24x24 building. I would pull permits for electrical for safety considerations, but if it's just a garage, no need for the rest like plumbing, heating, insulating, etc imho, but just check with your local building inspector and let him know you want it to be safe and meet the codes to pass. Seems like a bit of solar panels, solar converter, batteries, inverter, mini-split would be very nice as well and you could make it a smaller, less expensive system that adds heating, AC cooling, and some AC power. Just some thoughts for consideration, but do ask your building inspectors what they advise, and it's pretty easy to know the NEC codes.

    1. Patrick_OSullivan | | #3

      Thanks. I want the whole space actually conditioned. Power is not an issue.

      The crux of it is: the insulation requirements in the IRC do not make sense for a small outbuilding, at least in climate zone 4A.

      1. Optimal | | #4

        Yes, I agree. Too many stupid laws, but I do agree with the NEC and HVAC codes and many others. It sucks that I can not collect any water runoff from my roof (illegal) and at the same time am charged for that water runoff from my roof. I'm in Colorado, so it's nuts hear, very liberal lol. You may consider asking a contractor to review your build plan before consulting the building inspectors. Some codes are ignored under certain situations. Best of luck to ya!

  2. Optimal | | #2

    Oops, my apologies as I thought this was a pre-existing external building, however, what I said I think still works, but you will need more permits and possibly investigate a 220V 30A line from your house if needed, but they you may need a larger breaker box on your house to source that.

  3. Expert Member


    Here it would be entirely dependent on the intended use. The insulation and other requirements would not kick in unless it was being occupied as a dwelling, and certainly not for a workshop, whether it was conditioned or not.

    Where things get confusing are the grey area uses, like home offices, or bunkhouses where people can sleep, but that don't have cooking facilities. These typically aren't aren't subject to the energy requirements, but have to follow safely ones around access to exits, smoke detectors, etc.

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