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Think About Barndominium Insulation BEFORE Building

Think About Barndominium Insulation BEFORE Building

Regular readers are probably beginning to wonder why I have so many requests for information on how to insulate buildings AFTER they have been erected.

Me, too.

Insulation is crucial to your barndominium’s long term thermal performance. Doing it wrong can be expensive, both up front, as well as over lifetime of heating and/or cooling.

Reader JAMES in MILTON writes:

“Hello, I could really use your advice. I’m having a 48′ x 48′ wood barn built in Georgia with a 1,200 square foot apartment/ loft on the second floor. The purlins on the barn will be 8″ thick with 24″ spacing (center to center). The barn’s ceiling will be attached to the bottom (interior) side of the purlins. Plywood, the roofing underlayment, and the metal roof will be installed to the top (outer) side of the purlins. I’m looking to put insulation in-between the purlins to achieve (as close to) an r-40 insulation rating. Originally, I was going to get 2″ r-10 foam board insulation and layer them in between the purlins (up to the 8″), but prices for form board insulation increased again in my area and is having me rethink my plan (went from $40 to $60 a sheet). Plus, I would have to cut each foam board to fit in between the purlins, which is time consuming. I’m considering other options, but really don’t have the construction background to know which direction to go. From what I’ve read online, my setup would be an unvented space, limiting my options to spray foam (closed cell), foam board insulation or structural insulated panels (which goes on top of and not in between the purlins). I’ve also read I could install a layer of closed cell spray foam inside the purlins cavity but against the underside of the plywood. Afterwards, fill the rest of the purlin cavity with an air permeable insulation, such as faced fiberglass batts insulation. But I’m not sure if this option still requires venting. What is the best option when installing insulation in between purlins? Would foam board insulation work well? If so, other than cutting to size, would I have to do anything else? Thank you in advance for your help.”

Mike the Pole Barn Guru says:

Welcome to challenges of trying to get adequate insulation when finishing the underside of roof purlins.

Fulton County is Climate Zone 3A. 2021 IEEC requires ceilings to have a minimum R-49 – going to be tough to get unless you were to closed cell spray foam on the entire cavity.

You could do 2″ of closed cell spray foam directly to the underside of your roof deck (R-14), then fill the balance of the cavity with unfaced rockwool batts (roughly R-17). You do not want a vapor barrier below batts as this would trap air between two vapor barriers. Kraft facing on fiberglass batts is a vapor barrier and fiberglass is negatively affected by any moisture (even 1.5% moisture content can reduce R value by 50%).

Foam board will be highly labor intensive, difficult to air seal, provides a lesser R value than the same thickness of closed cell spray foam and at $60 a sheet, is approaching price of spray foam.

Another option would be to fill the cavity with unfaced rockwool batts (roughly R-23) then add two layers of 2″ R-10 foam board below purlins before your interior finish. It might be difficult to source rockwool batts 7-1/4″ thick, so may require doubling 3-1/2″ batts.

This entry was posted in Pole Building How To Guides, Pole Barn Planning, Pole Barn Structure, Ventilation, Barndominium, Insulation, Pole Barn Questions and tagged rock wool batts, IEEC, Kraft facing on fiberglass batts, vapor barrier, foam board, closed cell spray foam, roof deck, unfaced rock wool batts on December 13, 2022 by admin.

Corner Trim, Metal Roof Install Issue, and Insulation Solutions

This Wednesday the Pole Barn Guru answers reader questions about what trim to use on building corners, an issue of installing metal to roof that is extremely out of square, and best options to insulate a building.

DEAR POLE BARN GURU: Good afternoon! Looking to see what trim to use on the corners? https://www.hansenpolebuildings.com/2015/10/horizon-steel-siding/ Sincerely, KYLEIGH

DEAR KYLEIGH: Order standard Corner Trims and place pre-formed foam Outside Closure strips between horizontal steel siding and trims.

DEAR POLE BARN GURU: How much more difficult would it be to put the metal roof on if you can’t square the roof trusses. Because the posts were not cemented in properly. We are 8′ out of square on a 24’x50′. Would it be possible to square being that far out? TOM in BLOOMSBURG

DEAR TOM: I want my roof planes to be square within 1/8th inch before attempting to run steel. At 8′ out of square, I would have pulled out all offending posts and started over again. What you have will be impossible to properly roof and would require cutting every sheet of steel at eaves to even get a straight overhang line.

DEAR POLE BARN GURU: Just finished 40x60x16 pole barn and am looking to insulate. Building wrap was installed on exterior walls and roof has double bubble. Wondering how to manage moisture inside the building. Slab is insulated under as well as a vapor barrier. Interior walls and ceiling will be finished with steel liner panel. I’d like to spray foam entire building with open cell spray foam walls and roof deck. Would I need to install a vapor barrier between foam and steel liner panels? Building has attic trusses and the room will also be conditioned separately from garage space. Thanks KYLE in COXSACKIE

DEAR KYLE: I would not spray foam to building wrap, as it causes more problems than it solves. https://www.hansenpolebuildings.com/2020/04/spray-foam-insulation-3/
For walls, I would use unfaced rock wool batts, with a well-sealed interior vapor barrier. You do not need a vapor barrier between ceiling liner panels and attic spray foam. Personally, I would blow in fiberglass above ceiling liner panels and ventilate the dead attic space.

It might be necessary to mechanically dehumidify your building.

This entry was posted in Ventilation, Building Interior, Insulation, Pole Barn Heating, Pole Barn Questions, Pole Barn Design, Roofing Materials, Constructing a Pole Building, Pole Building Siding and tagged Ventilation, square roof, corner trims, unfaced rock wool batts, metal trims, insulation, install roof steel, vapor barrier on November 16, 2022 by admin.

Insulating an Apartment in a Steel Truss Pole Barn

Reader JONATHAN in AUGUSTA writes:

“First of all, thank you for having a wonderful resource put together in one place for fellow DIYers such as myself. I am currently in the process of constructing a 30x60x11 pole barn. So far I have the roof put up; metal trusses with 2×6 wood purlins, synthetic underlayment and metal R panel. I will be building a 30×24 “apartment” inside, think box inside of a building with the remainder being used as a shop. 3 sides of the apartment will be the exterior walls of the pole barn with the 4th side splitting the barn almost in half. I will have mechanical ventilation in the form of an exhaust fan cut into the side of the building sized to the 30×36 portion with an appropriately sized louver that I intend on using when necessary when working in the shop. The apartment will have HVAC. I am looking for the best method to insulate the roof. Vented/unvented? Spray foam? Radiant barrier nailed to the bottom of the purlins? I plan to house wrap the walls and install Rockwool to insulate them but was unsure about the roof. There are so many conflicting methods out there I just want to get it right the first time. I am in a hot humid part of the south. I look forward to your thoughts on this and thank you in advance for any advice.”

Mike the Pole Barn Guru advises:

Thank you for your kind words. Obviously we are somewhat self-serving as many of our blog readers understand Hansen Pole Buildings caters to those who want to DIY and realize there is a good chance we can assist them in reaching their ultimate goals, without undue road bumps and pot holes.

You have some challenges happening here (aka pot holes), in part due to your choice of roof systems. Those trusses are not designed for a ceiling and 2×6 roof purlins at this span will deflect too far to allow for sheetrock to be applied to them, or to give an adequate depth insulation cavity.

If I was in your position, I would frame in 8 or 9 foot tall walls for apartment area, with ceiling joists above. I would then use unfaced rock wool batts between ceiling joists to R-30 (Climate Zones 0 and 1) or R-49 (Zones 2 and 3). Use 5/8″ Type X sheetrock for apartment ceiling and wall between apartment and shop (personally I like 5/8″ everywhere).

Ventilate balance of building otherwise you will most probably experience condensation challenges.