Tag Archives: roof truss bottom chords

How to Insulate My Pole Barn Roof

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.

Spot Problems with This Pole Barn Photo

Spot Problems With This Pole Barn Photo

One of my Facebook friends had posted this as a timeline photo as it brought back to her fond memories of a childhood spent frolicking in hay lofts. It was so bad, I just had to save it.

So, what’s wrong with this photo anyhow?

Obviously bird excrement over everything does not pose a structural problem, but one which I would have been trying to minimize, if not avoid. One thing which was leading birds into building – excellent nesting material provided by what was once a vinyl faced fiberglass condensation control blanket (aka Metal Building Insulation).

Long ago I had espoused about joys (or lack thereof) involved in installation of Metal Building Insulation (https://www.hansenpolebuildings.com/2011/11/metal-building-insulation-in-pole-buildings-part-i/). For those of you readers who did not click upon link and read it in full, suffice it to say birds love fiberglass.

Once condensation control blanket was torn apart – there was nothing left to prevent condensation from occurring below roof steel.

Moving forward, just glancing upon structure supporting hay loft, I would suspect a high degree of under design with only chance keeping it from meeting its demise.

All sorts of things are seen hanging from trusses. Amongst these are a block and tackle, which I suspect has been used to lift bales of hay into loft. Fortunately, individual small hay bales are relatively light, as I am pretty sure trusses were not designed to support added point load weights.

While not most effective structurally, trusses can be designed to be placed upon each side of a column – provided they are done correctly. Blocking should be placed between truss bottom chords, in order to prevent weak axis bending. A bare minimum would be every ten feet.

I see no web bracing, making this highly suspect. Older barns tend to have had bracing needs neglected. Single trusses (when placed not nailed directly face-to-face into a pair, they are single) require a great deal of bracing.

Knee braces are what I see as biggest structural issue. Not only are knee braces ineffective (https://www.hansenpolebuildings.com/2012/01/post-frame-construction-knee-braces/), but when installed improperly (as in photo) they are potentially throwing a load into roof truss bottom chords trusses were not designed to withstand.

Feel free to chip in with your observations.