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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 Barndominium, Insulation, Pole Barn Questions, Pole Building How To Guides, Pole Barn Planning, Pole Barn Structure, Ventilation and tagged , , , , , , , on by .

Fun With a Cheap Steel Truss Pole Building

Most of our country is unfamiliar with low budget steel truss pole barns produced and sold primarily in Southeastern states. There is a reason these are prevalent where there is no snow – just in case you were wondering.

Disclaimer, I have no issues at all with prefabricated light gauge steel trusses, provided they have been manufactured to engineer sealed drawings, specific to loading conditions where they will be put into use. AND if they are fabricated by a certified welder (rarely occurs).

Reader KEVIN in COLUMBIA writes:

“Hi Guru,

 

I recently purchased a home and the property included a 32×84 Pole barn. The barn was never dried in and was barely completed by the previous owner. However, everything is solid, square and plum; with the exception of a few pieces of steel on the roof that were never installed, it is a solid structure. Immediately after purchasing the home I had a monolithic slab poured under half of the structure that will become the foundation for the home of my new shop. I am quite comfortable with carpentry, but not so much with insulation. How do I go about condensation proofing the roof? I really do not want to pull the existing roof panels off to lay a vapor barrier over the purlins. My intention is to have a well ventilated attic, insulate the walls, and blow in insulation over the ceiling. I have heard of some people installing foam board to the exposed steel. Spray foam is an option, but one that is out of my price range for the moment. I have attached some images for your inspection. The 3D CAD models should provide a better illustration of what is under the roof. I look forward to your response.”


Kevin is now experiencing joys associated with buildings sold ‘on the cheap’ – with barely enough materials to get a roof on with a minimal budget. It would have been so simple for this building to have been originally sold and erected with provisions to control roof condensation. Either a Reflective Radiant Barrier (RRB) or an Integral Condensation Control (ICC) would have easily avoided your current situation.

This style of building does not lend itself well to installation of a ceiling (there are no clips along truss bottom chords to accept ceiling joists). My educated guess is these trusses are not designed to support weight of a ceiling. With 2×6 purlins spanning 12 feet, they are sadly not stiff enough to keep drywall joints from cracking – so you are going to be faced with lots of limitations.

Foam board might be a solution, however you would need to have each panel 100% air sealed between purlins in order to do so. Chances of success range close to zero. You are left with two choices – remove roof steel, install a RRB and reinstall roofing or two inches of closed cell spray foam (roughly $5700). Hopefully you have poured your slab on grade over a well-sealed vapor barrier, if not – use a sealant on top of it (not as effective, but better than nothing).

 

This entry was posted in Trusses, Ventilation, Insulation, Budget, Pole Barn Questions, Pole Building Comparisons, Pole Building How To Guides and tagged , , , , , , , , , on by .

How to Insulate My Post Frame Garage

How to Insulate

I fear “how to insulate my post frame (fill in the blank)” is going to be my most answered topic for the next decade. Energy efficiency is the “hot” topic right now and sadly there are more folks trying to solve what they already have, than there were those who planned for it correctly in the beginning.

Reader ERIC in FENELTON writes:

“Hello, I am wondering what the best and most cost effective way to insulate my post frame garage would be. I recently erected a 32’x48’post frame garage with glulam posts on 8’ centers, girts and purlins on 2’ Center’s, trusses on 4’ centers with 1’ overhangs with center soffit and ridge vent. Walls and roof are steel with double bubble between purlins and roof steel and tyvek between hurts and the wall steel. I will be building a wall to separate one of the bays as a metal shop for welding and fabricating. This will be the only bay that is heated and is 32’x21’. I am on a budget but my biggest concern is moisture. I installed the tyvek and double bubble hoping to positively effect the problem but am still hesitant to put fiberglass in the
walls but spray foam is out of my price range. I have seen some people cut 1 1/2” foam board to fit between the wall girts and either stop there or then frame traditional walls between the posts and add R13-R19 faced insulation. Is this an adequate way to insulate and will the foamboard keep moisture from the fiberglass? I will definitely be framing between posts and then covering with painted OSB regardless of the insulation method I choose. Also, I was leaning toward using fiberglass batts in the ceiling and then using the white liner steel under the trusses. They are 2×6 top and bottom cord trusses and rated for a ceiling. Fiberglass in the ceiling gives me the same moisture
concerns however. So I guess my question is, now that you know about my building, what is the best abs most cost effective way to insulate the portion of the building and avoid moisture? Spray foam is out of the question due to costs. I have been doing a ton of research but get different answers everywhere I go. Any help will be greatly appreciated. Thank you.”

Mike the Pole Barn Guru
As long as the Tyvek is well sealed, you will not be gaining moisture from the outside on the walls. What you need to create is a dry wall cavity. Completely fill the wall with unfaced fiberglass (you might consider using BIBs https://www.hansenpolebuildings.com/2011/11/bibs/)
and cover the interior of the wall with a well sealed vapor barrier (clear visqueen will do nicely). Cutting foam board is an exercise in
futility unless you can figure out how to completely seal it, if you
stop at this point.

For your ceiling – there is a good chance you will experience
condensation on the underside of the steel ceiling liner panels. With
your vented eave and ridge, blown in fiberglass is probably the best
answer. If you do not have raised heel trusses, you should probably look
at spray foaming the first couple of feet of the ceiling area in order
to reduce heat loss from not being able to gain full thickness of the
fiberglass.

This entry was posted in Ventilation, Insulation, Pole Barn Questions, Roofing Materials, Pole Building How To Guides and tagged , , , , on by .

Rigid Foam Plastic Insulation

One of the joys of what I do is I get to learn new things every day. I’ve often thought to myself, the day I stop learning, is the day I am dead.

In today’s lesson….one of our clients has taken his engineer sealed plans to his Building Department to obtain a building permit. The building is designed with interior steel liner panels (not my personal favorite choice – but a topic for a future blog). The panels are to cover fiberglass insulation.

Sounds pretty straight forward so far, at least to me…..

Until our client told the Plans Examiner he is going to insulate the building using rigid foam plastic insulation.

What is rigid foam plastic insulation? An example would be Rmax’s R-Matte Plus-3, which is a rigid foam plastic thermal insulation board composed of environmentally sound, closed cell, polyisocyanurate foam bonded to a durable white-matte (non-glare) aluminum facer and a reflective reinforced aluminum facer. Basically – any polyisocyanurate sheathing.

The plans examiner came up with the following, “…foam plastic shall be separated from the interior of a building by an approved thermal barrier of 0.5-inch gypsum wallboard or equivalent thermal barrier material that will limit the average temperature rise of the unexposed surface to not more than 250 degrees F after 15 minutes of fire exposure, complying with the standard time-temperature curve of ASTM E 119…”

In layman’s terms, if your idea is to insulate your new pole building using polyisocyanurate insulation boards, plan upon having to place ½” drywall on the inside wall. This may result in costs which were not budgeted for, not just for the drywall, but to have the framing and weight capacity of the building designed to be able to support it.

My recommendation? Compare total costs between this and other options, such as fiberglass, before making a commitment to rigid foam plastic insulation.  It’s not that it is a bad choice – not at all.  It’s just that your building needs to be designed to support it.  And of course, your buildings need to meet the code for it so your plans examiner is in happy-land.

This entry was posted in Building Department, Pole Barn Planning, Pole Barn Structure and tagged , , on by .
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