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Insulating a Quonset hut - (Can we make a sandwich?)

Imagine an arched metal Quonset hut, such as an older aircraft hanger. The skin of the building is structural; there is no structure under. The buildings are a set of panels which are bolted together, weatherstripped to form an arch. Each arch is bolted to the next to form the building.

Many of these structures are used a workshops or garages, we would like to use one as a studio. Typically these are insulated using either spray foam or fiberglass that is pinned to the shell, which looks somewhat like a quilt.

In our case, we are thinking of building a smaller second shell to go inside, so envison a shell over a shell. The idea would be to build the outer shell, frame the end walls and then spray closed cell foam, 4-6" (or more) to create a a "weather tight" area.

The second shell would be 1 feet (or more) from the outer shell, so there would be a gap. The idea that we are considering is as each arch is built, set it in place and then use blown in dense packed cellulose to fill the area between the inner shell and the foamed outer shell. Erect arch, place arch, insulate arch then repeat until the inner shell is compete. Last arch would be tricky, but considering access on the end wall to fill in the space or build each panel of the arch one at a time and then insulate with the final panel with access ports to blow in insulation...

Assume a heat recovery ventilator and a mitsubishi heat pump for the space.

This is a running idea, but when crafting an insulated sandwich like this what other items should be taken into consideration?

The goal is to have metal arched interior that is insulated.

Thanks,

Doug

Asked by Doug Reid
Posted Fri, 05/04/2012 - 07:01
Edited Fri, 05/04/2012 - 07:40

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4 Answers

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1.
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Doug,
1. You don't want to have the spray foam truck arrive 8 different times to spray 8 different arches. You want to get all of your Quonset hut segments installed, and then invite your spray foam truck to come for a single visit.

2. It sounds like you are proposing a "flash and fill" application with a layer of spray foam against the steel and an inner layer of cellulose. That will work, as long as you follow the usual caveat: your spray foam needs to be thick enough to keep the interior surface of the foam above the dew point in winter. For more information on these calculations, see How to Build an Insulated Cathedral Ceiling.

As you probably know, only closed-cell spray foam (not open-cell spray foam) can be used with this type of flash-and-fill job.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 05/04/2012 - 07:38

2.
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@Martin. Thanks. The idea is that the foam-guy only shows up once to foam the outer shell and then the end walls. The gap between the inner and outer foamed arched would be filled with dense packed cellulose and I was thinking that we rent the machine from Home Depot or build all the arches ahead of time, stage them and then work with the contractor to be onsite over a day or so to fill the arches as they are erected. With good planning and hands we might be able to erect the inner shell in a day or two.

Answered by Doug Reid
Posted Fri, 05/04/2012 - 07:44

3.
Helpful? 0

@Doug, I have been thinking about a similar double-shelled quonset method as well. The step-by-step construction approach I had envisioned is the same as you described; build an inner shell, insulate, then add the outer shell with at least a one-foot cavity. However, I was thinking the you could use typical batt/roll insulation in the cavity. I wonder what you and Martin think of this approach?

Answered by KEN CHOAT
Posted Thu, 10/11/2012 - 12:13

4.
Helpful? 0

@Doug, I have been thinking about a similar double-shelled quonset method as well. The step-by-step construction approach I had envisioned is the same as you described; build an inner shell, insulate, then add the outer shell with at least a one-foot cavity. However, I was thinking the you could use typical batt/roll insulation in the cavity. I wonder what you and Martin think of this approach?

Answered by KEN CHOAT
Posted Thu, 10/11/2012 - 12:13

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