Insulating a Post-and-Frame Building
Hello community! I’m excited to get your ideas and opinions on my new post frame building design. Shout out to Martin Holladay for his article “Insulating a Pole Barn” in which he points to the house built by Ben Freed as an example of a well insulated post framed building. In this Q&A I’d like to incrementally advance the discussion on this site with regards to building a good post framed envelope to be heated in a cold climate. This post is about new construction so it won’t try to directly answer the questions of people trying to turn old pole barns into something else.
The plan I’m developing is for a 40’x60’x24’H carriage home (home above garage space) to be built on rural land I’m purchasing near my current home. I’m the owner/builder of my current home as well as the new one that I’m planning. The area is climate zone 6 in the Canadian rocky mountains. We don’t having zoning or permitting in my area so I am able to build without restrictions but I intend to honour the building codes unless I have a good reason to vary from their wisdom. My goal with this building is to erect the outer shell efficiently and get it insulated to use as a warehouse and workshop during the rest of the land development and remainder of the home build. In the coming years I plan to develop both a small apartment inside the building as well as a full upper mezzanine home. Cost efficiency is a primary objective for this project along with durability.
Building dimensions are 40’x60’x24’H. The height allows for a 13’H garage below the upper home. A thickened edge slab on grade, frost protected shallow foundation forms the base. Attic-style roof trusses above for utility access; unvented attic. Walls built with 6″x8″ laminated posts on 4′ centres, joined with 2×6 girts. No wall sheathing is necessary for the sake of shear strength as other details provide for that. Siding and roofing are ribbed or standing seam metal. I have been considering how best to insulate this building in a way that is time efficient, cost efficient and maximally durable. I want good air control but I don’t want to bird-dog every member of a large crew taping seams during the initial erection of the building. To this end I have developed an idea to insulate this whole envelope with 5″ closed cell spray foam directly applied to the interior side of the factory-painted metal siding and roofing, as soon as the building is closed in.
I like this method for the following advantages:
*exceptional air control
*no detailing of exterior or interior membranes
*eliminating sheathing and membrane $$ offsets spray foam $$$
*added strength of a fully “glued” structure
*industry bodies recognise this method of applying foam insulation directly to painted metal (see SPFA-134)
I see the following weaknesses, which I am comfortable accepting:
*cost of spray foam is higher than blanket insulation and blown-in cellulose
*re-roofing requires strapping over top of old roofing to add second roof
*requires thoughtful details around siding penetrations
I have the following concerns:
*spray foam off-gassing HFO and other gasses into building
*how to allow drying of wood around windows etc
*differential expansion of metal and wood components
*cracking and gapping of foam over time
*method is not yet widely used in residential construction
*what may I have missed?
So my thoughtful friends, what do you think about these methods? I appreciate that this idea is a significant break from the methods popular on this forum which tend to focus on great sheathing and membrane details. Can anyone offer advice or insight from experience with a similar build to mine, perhaps in the commercial space?
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