Retrofitting for an Interior Workshop
Loyal reader LAURI in NORTH BRANCH writes:
“Thank you ahead of time for your generous gift of answering these questions. I love your blog. I have a 40 x 60 pole barn and doing an interior workshop of 25 x 40. Exterior walls (only in workshop area) have no vapor retarder and have R15 in Owens Corning pink board topped with 3/4″ plywood. I put in a tin ceiling (in the workshop area only) with no vapor retarder. I have not insulated the attic area above the workshop yet. It is well ventilated with eave and ridge vents. I put in a 2 x 6 partition wall which will separate the workshop area from uninsulated storage area. I will infrequently be using some form of AC on the hottest MN days and only occasionally use some form of heat (forced air, Mr. Heater or torpedo heater) to heat the workshop. The floors are sealed but without a vapor retarder under the concrete. I’m torn on what to do with the partition wall insulation. Vapor retarder or no Vapor retarder on the shop side? The interior shop wall covering will be 3/4″ plywood and the storage side will be OSB I have on hand. I’m thinking a wool product for minimizing any potential for mold. What insulation should I use for the attic space at truss chord level? I think you lean towards a blown in but can I leave the underside of the roof uninsulated? Vapor barrier or no vapor barrier on interior partition wall? What questions am I not asking that I should be? Thanks again for your wisdom. Nice to feel that someone has our interests at heart. Wish I would have found you guys before I built. Maybe a second one will be in our future where we can pay back the kindness.”
Mike the Pole Barn Guru says:
Thank you for your kind words, they are greatly appreciated.
My goal is to always try to assist people from making crucial mistakes they will regret forever.
My concerns for your workshop area are going to be ones of moisture – although your slab on grade has been sealed, it has no vapor barrier underneath, so you are probably yet going to have moisture passing through. Heating with either propane or kerosene will be adding even more moisture into this area.
I would look at design solutions allowing moisture to pass out of your workshop, and not in. For those interior walls, unfaced Rockwool batts, with a housewrap on the cold storage side of studs. Ceiling, if you can find it, use blown granulated Rockwool, as it is unaffected by moisture. Otherwise use Rockwool batts, overlaying layers 90 degrees to each other.
If you have no thermal break between roof purlins and roof steel, you are likely to have some condensation challenges, even if well ventilated. Keep a close watch and if you see condensation beginning to form, have two inches of closed cell spray foam applied to the underside of roof steel, otherwise it will rain on you.
Looking for Advice on Insulating My Pole Barn Walls
MATTHEW in CENTRAL ILLINOIS writes:
“Hello! I am a member of the Facebook pole barns and buildings page and see your post with advice often. I honor your opinions. I am wondering if you can help me out. I have a 30×48 pole barn in central Illinois. Concrete floor. I don’t believe there to be a moisture barrier under the concrete. I am wanting some advice on how to finish the inside. I’m thinking about doing bookshelf girts instead of interior girts attached to the poles. Should I use 2×4’s or 2×6’s? My thought is 2×6’s, but should I put them up against the exterior girts, or away from them to allow a space for insulation? There is no house wrap or vapor barrier on the inside of the metal. I would like to heat it as needed during the winter, but only when I’m working on a project. I wouldn’t have continuous heat. What insulation would be safest to use to prevent moisture along with being somewhat affordable? I do have a place about a half mile away that sells factory seconds of various foam boards. I have also heard good things about rock wool. Spray foam seems to be the most popular, but also can be more expensive. What are your suggestions taking in consideration of no current vapor barriers, location, and intermittent usage? “
Thank you for reaching out to me. Please message me any time with questions.
If unsure of whether there is a vapor barrier under your concrete slab, start by sealing it.
Here is how: https://www.hansenpolebuildings.com/2019/02/how-to-properly-apply-post-frame-concrete-sealant/
This sealant came highly recommended: https://www.hansenpolebuildings.com/2018/11/siloxa-tek-8505-concrete-sealant/
2×4 #2 bookshelf girts should be stiff enough on your small span between columns to prevent undue deflection of interior finishes, as well as limiting thermal transfer. Hold them flush to the inside of existing wall columns.
I would look to fill your insulation cavity with Rockwool batts, with a well-sealed vapor barrier on the interior.
How to Insulate My Pole Barn Roof
Reader JEREMY in GREENBRIER writes:
“Looking at building a 50x60x15 pole barn 20 miles north of Nashville, TN. I’m needing recommendations for the best way to insulate. I’m using scissor trusses with no ceiling and I’m planning metal panels on the inside walls. I’m thinking 2×4 girts on the outside of the poles and 2×6 bookshelf girts. Tyvek wrapped and Rockwool between bookshelf girts. I’m not sure how to insulate the ceiling or roof. I will be conditioning the space and keeping it between 78-55 degrees year round. Thanks.”
Mike the Pole Barn Guru says:
Our oldest daughter lives just south of you!
While I realize you have this building pretty well planned out, I will throw out some ideas. Hopefully they will allow you to keep more of your hard earned dollars in your wallet.
With a 50′ span, you might want to consider increasing wall height, rather than using scissor trusses. Chances are good it will be less costly and will provide full height utilization from wall-to-wall.
Rather than using a combination wall girt, if you just do 2×8 bookshelf girts it will take less materials and time to install.
Robertson County is in Climate Zone 4A, where 2021 International Energy Conservation Code (IECC) requires R60 in roofs and R30 in walls. You can meet wall requirements with 7-1/4″ Rockwool (https://www.hansenpolebuildings.com/2013/03/roxul-insulation/) (batts . If you are trying to insulate the plane of your roof, you will be pretty much limited to spray foam insulation. You could do 2″ of closed cell insulation applied to the underside of roof steel plus 13″ of open cell or 3 & 11, etc. Any of these will become expensive design solutions. You also will end up conditioning a tremendous amount of area above truss bottom chords.
How I would do it….
Order 16″ raised heel trusses. Roof steel with an Integral Condensation Control (https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/) factory applied. Vent soffits and ridge in correct ratios (https://www.hansenpolebuildings.com/2018/03/adequate-eave-ridge-ventilation/). Install a ceiling, blow in R-60 of granulated Rockwool. This overall combination will be far less expensive than spray foam and certainly far less expensive to climate control.
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.
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.
Moisture Barrier for a North Idaho Hangar
Reader BILL in SANDPOINT writes:
“Hey guru! Question about insulation – moisture barrier. We are under construction on a 64×70 post frame aircraft hangar in North Idaho. The eave height is 19 feet, plus a two foot heel. There are no overhangs. Roof pitch is 3:12 and the ceiling is vaulted 1:12 there will be a 58 foot wide by 18 foot tall hanger door. Attic venting will be from gable end vents. The roof will be sheathed with 7/16 OSB and receive 30# felt under the 26 gauge PBR. The walls will be sheathed 7/16 OSB and house wrapped under the 29 gauge steel panels. The plan is to install metal liner panel on the ceiling and 5/8″ drywall on the walls. Insulation will be r49 blow in the attic, and r25 unfaced batts in the walls. The hanger door is yet to be determined, but it might also be unfaced batts under a metal liner. Two 125,000 BTU radiant tube heaters will be installed in the ceiling. They will be vented outside and will draw combustion air from outside. I am thinking that it makes sense to install a full vapor barrier for the walls and the ceiling, but would appreciate your thoughts on the matter.”
Mike the Pole Barn Guru writes:
Before we get to your question, I have some concerns….
First – you are putting a 58 foot wide door in a 64 foot endwall. This leaves only three feet of solid wall on each side of your door opening. These areas need to be shearwalls and maximum aspect ratio for a shearwall is 4:1 (four feet of height for every foot of width). With a three foot wide shearwall your maximum opening height would be 12 feet. You are likely to experience some tremendous racking problems (if not a failure) on your door endwall.
Second – trying to ventilate a 4480 square foot dead attic space with gable vents will require 1075.2 square inches of NFVA (Net Free Ventilating Area) in each endwall and this is providing half of NFVA is located in each upper and lower half of each endwall. You could accomplish this with say four 24″ x 36″ galvanized gable vents each end, however this might not be your most aesthetically pleasing design solution. Downside of gable vents is once you get past your first pair of trusses, airflow becomes negligible. I would be much happier with vents in your sidewalls (in area of truss heels) as an intake, combined with continuous ridge venting.
If it were me – I would use unfaced R-30 rockwool batts in sidewalls (they are not affected by moisture and R value does not degrade over time like fiberglass does) with a well-sealed interior vapor barrier before hanging drywall. This would allow your walls to dry to outside. Ceiling should not have a vapor barrier, as you want moist air to be able to escape into your well ventilated attic. I would blow in R-60 of rockwool.
Best of success with your build.
Saving a Poorly Designed a Crawl Space
Reader GEORGE in VIENNA writes:
“I am substantially replacing rotted parts of an existing building set on short 6×6 treated posts which are in good condition. above the posts it is conventional platform construction, and untreated. Unfortunately, the original builder set the building partially into the side of a hill in an attempt to use thermal mass and reduce energy use in its off-grid location. The uphill side was backfilled to a height of approximately 30″ above the interior floor, which is OSB over untreated 2×12 beams and untreated 2×6 joists. Skirting to keep out moisture was untreated plywood, poly sheet, and Styrofoam block insulation. In 6 years, there is substantial rot of the perimeter plywood, perimeter 2×12 rim joists, some 2×6 floor joists, some areas of the OSB flooring, the untreated sole plate and a few studs above. Otherwise the building walls, windows, doors, roof trusses, metal roof, insulation, etc., are well made and in good condition. We are temporarily supporting the building from below and removing the failed materials all the way around. We are removing the backfilled dirt on three sides to expose the posts and provide airflow underneath. All rim joists, beams, and floor joists will be replaced with treated materials. I am looking for advice in two areas (1) floor insulation, either under or over the OSB, and (2) treated skirting around the perimeter which would allow partial backfill and maintain ventilation.”
Mike the Pole Barn Guru says:
You really have two options:
You could condition your crawl space – this would require a 6mil or thicker, well-sealed vapor barrier to cover underlying soil and up perimeter walls to floor joists. There would be no vents with this method, however an air-circulating device must be provided. Perimeter walls should be insulated using either closed cell spray foam or rock wool batts.
From Building Code Section 308.3, Unventilated Crawl Spaces
|The air-circulating device must move at least 1 cubic foot of air per 50 square feet of crawl space area. The crawl space floor area must be completely sealed with a vapor-retarding material. The edges of the vapor retarder must be lapped up against the inner foundation walls.
Read more about encapsulated crawl spaces here: https://www.hansenpolebuildings.com/2020/11/11-reasons-why-barndominium-crawl-space-encapsulation-is-important/
Or – have an unconditioned crawl space, where your vapor barrier would cover the ground surface. Insulation would ideally be beneath OSB – between floor joists. Again, same choices for insulation – just between joists. With this choice foundation vents would need to be added to perimeter walls.
Most building codes require 1 square foot of open ventilation area for every 150 square feet of crawlspace. Generally, Automatic Foundation Vents have 50 inches of net free area per vent. Therefore, install one vent for every 50 square feet of crawlspace.
FDN (Foundation) rated pressure preservative treated plywood will probably be your best skirting material.