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Community and Q&A

How to insulate a workshop?

Kendo64 | Posted in General Questions on

Planning on having a 60’ (L) x 30’ (W) x 12’ (H) post and frame (pole building), built in climate zone 5B. The building will be bisected by a 2×6 interior wall so that 36’ x 30’ will be used as an un-insulated garage and the remaining 24’ x 30’ will serve as an insulated and conditioned workshop. The floor will be 4” concrete slab on grade poured after the building is erected. Exterior walls are metal panels mounted to wall girts and the roof is also metal on engineered trusses.
How best to insulate just the work shop area? I have some ideas, but I also need some direction as well. Note: While I know this is a website about constructing really good homes, this is a workshop, so my budget is limited.

Ceiling: As the workshop area only needs a 10’ ceiling, I was considering using raised heel trusses for that area which would lower the ceiling from the 12’ garage height and allow me to use blown in cellulose above the sheet rocked finished ceiling. The trusses above the garage space and the workshop would be open to the garage space. Any problems with this setup?

Walls: Exterior walls are metal. I would add interior commercial wall girts (horizontal 2×4’s, 2’ spacing) to mount sheet rock. Wall thickness would be the same as a 2×6 stud wall. I was thinking BIB for the wall insulation. Do I need house wrap for the exterior walls? The interior wall will be sheet rocked on both sides how should this be insulated/house wrapped?

Floor: I do want to add 3” of foam sheet insulation under the workshop slab area, but at the same time I don’t need to insulate under the garage. What is the best way to create a thermal break in the concrete slab between the two areas? Install a pressure treated 2×6 in the concrete where the wall will be located?

Special floor question: In pole buildings the 2×6 or 2×8 splash board at the bottom of the wall typically serves as a form when pouring the concrete slab. Can I add solid foam insulation to the splash board or is there a better method to insulate this area?

Thanks in advance, Ken

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  1. GBA Editor
    Martin Holladay | | #1

    Post frame buildings (or pole barns) face special challenges.

    This type of building can be inexpensive, and (as long as you don't try to heat it or cool it) will work well to keep rain off of equipment, animals, or hay.

    A pole barn doesn't work well if you intend to try to insulate the walls and roof. Here are links to previous Q&A threads on the topic:

    Here are some quotes from some of the answers I posted to these previous questions. (Forgive the repetition):

    "The main problem with insulating a pole barn is creating a good air barrier. There are many opportunities for air leakage: between the insulated sections of the wall and the vertical posts; at the base of the wall (which either meets gravel or a concrete slab); and at the intersection of the wall and the insulated ceiling. You should strive for airtightness when you create this assembly. It won't be easy -- but do your best."

    "It's tough to insulate a pole barn. ... If you have a slab, we'll need to know your climate zone or location, so we can recommend whether you need a horizontal layer of rigid foam under the slab. Next, you still have issues of how to support the insulation. In most pole barns, you don't have studs. You have posts and horizontal nailers between the posts. This makes air sealing difficult, and using conventional insulation difficult. The best way to proceed is to work on the exterior side of your structural frame. Again, either SIPs or nailbase is one approach -- and if you use SIPs, you could skip the pole barn structure, and just build a SIP building. Another approach is to install a stud wall on the outside of your pole barn to hold the insulation -- but again, this raises the question, why not just build an ordinary building with stud-framed walls if you need it for insulation?"

    "I'm afraid that 'energy efficient pole building' is an oxymoron. If you want to make a pole building energy-efficient, you pretty much have to build an entirely new building -- either inside the pole building or outside the pole building -- to create an air barrier and provide somewhere to install the insulation. That's why people who are interested in energy efficiency don't choose dirt floors or pole construction. However, if you decide to let go of the idea of energy efficiency, you can certainly build a dirt-floored tiny house with a pole frame."

    "A much better plan would be to put most of your wall's R-value -- perhaps R-20 to R-40 -- on the exterior side of your posts, installed as a continuous layer of rigid foam. This would require you to frame up between your posts, of course, and to install exterior sheathing before you insulate -- negating any cost advantages to your framing choice. In short, post frame buildings are hard to air seal and insulate."

  2. GBA Editor
    Martin Holladay | | #2

    To answer some of your questions:

    Raised-heel trusses make sense. Insulating your attic floor with cellulose makes sense.

    Q. "Do I need housewrap for the exterior walls?"

    A. Yes, every wall needs a water-resistive barrier (WRB) behind the siding. Ideally, this WRB (for example, housewrap) is attached to a layer of wall sheathing (usually plywood or OSB) that has been installed with attention to airtightness. Your wall needs an exterior air barrier.

    Q. "The interior wall will be sheetrocked on both sides. How should this be insulated/house wrapped?"

    A. What do you mean, "sheetrocked on both sides"? Are you planning to install drywall on the exterior side of your insulated walls?

    Q. "What is the best way to create a thermal break in the concrete slab between the two areas? Install a pressure treated 2x6 in the concrete where the wall will be located?"

    A. I would separate the two slabs with vertical rigid foam (EPS or XPS). The vertical rigid foam should be at least 2 inches thick -- 4 inches is better. Of course, the entire exterior perimeter of your slab needs vertical rigid foam.

    Q. "Can I add solid foam insulation to the splash board or is there a better method to insulate this area?"

    A. Adding rigid foam to the interior side of your slab form is one way to proceed. If you don't want to do that, you would need to install insulation on the exterior side of this splash board (assuming that the splash board stays in place permanently).

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