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Community and Q&A

How do I cost effectively insulate the ceilings of my detached garage?

MattMcDIowa | Posted in Energy Efficiency and Durability on

I have a 22×22 detached garage with a 15×15 addition on the back (both gable roofs) that I’m turning into a shop. I live in Iowa and have run a gas line to it and have purchased a gas heater capable of heating. I would like to heat the garage at low heat and will crank it for shop time. Each space has 2×4 rafters, but no insulation, no ridge vent or other roof venting and only one of the two spaces allows free flowing air to enter the building through the rafters running beyond the building envelope as the 22x space has wood blocking. I would like the spaces to remain vaulted if possible and once insulated, would like to cover the ceiling in OSB if possible.
I can provide pics if needed.

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  1. GBA Editor
    Martin Holladay | | #1

    I think you forgot to ask a question.

  2. StudioGuy | | #2

    OK, well I have a question. I have a very similar space (detached 15 x 15 workshop behind my garage) and I'm trying to figure out the best heating and cooling solution. I've been looking at ductless mini-split systems, but am not convinced the heat pumps are sufficient for a not well insulated space. I would prefer the ductless solution because it is quiet (this workshop is a recording studio). Any suggestions?

  3. StudioGuy | | #3

    Oh, I forgot to mention that I have a gas line running into the room, and that I live in the northeast so the winters are pretty cold! Thanks in advance for any advice.

  4. kevin_in_denver | | #4

    You have scissor trusses?

  5. GBA Editor
    Martin Holladay | | #5

    It sounds like to want an unvented cathedral roof assembly. This type of roof requires either spray foam insulation on the underside of the roof sheathing or rigid foam insulation above the roof sheathing. If you install rigid foam insulation above the roof sheathing, you will need to replace the roofing.

    For more information on unvented cathedral ceilings, see How to Build an Insulated Cathedral Ceiling.

  6. GBA Editor
    Martin Holladay | | #6

    You wrote, "I've been looking at ductless mini-split systems, but am not convinced the heat pumps are sufficient for a not well insulated space."

    The first step of any heating system design is to perform a heat-loss calculation. A building that is not well insulated will require a heating system with a higher capacity than a building that is not well insulated. This is true no matter what type of heating system that you plan to install -- a furnace, a wood stove, or a minisplit.

    It usually makes more sense to tighten up a building and add adequate insulation rather than just installing a really big heating system.

    You write that you live in "the northeast." That's not very specific. But plenty of people in Vermont and Maine are heating buildings with ductless minisplits. If you anticipate a long spell of weather when the temperature never rises above -20 degrees F, you might want to consider installing some electric resistance baseboard heaters for backup heat.

    And if you are using this room as a recording studio, it obviously makes sense (a) to insulate the building well, since insulation cuts down on noise transmission, and (b) to turn off the ductless minisplit when you are recording, so that the sound of the fan doesn't interfere with the recording. If the building is well insulated, it will be comfortable for several hours, even when the minisplit is off.

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