Insulating Pole Barn Ceiling

[TC65023]

I have a new 45'X42' metal skinned, pole barn structure with 12 foot eave height that I plan on using for a heated farm shop located in Central Missouri, Region 5. I live on a 80 acre farm in a rural area of a county where there is no enforced building codes, so I have a little more latitude design-wise than normal. That said, I still want to maintain good building construction standards and techniques.

The roof and walls have 2 inches of polyfaced fiberglass for condensation control.

The wood trusses are 9' on center and supported by 6X6 posts. The trusses are designed for 5 lb LL on the lower chord. I have installed used 2X6 wood decking as ceiling purlins at 2 foot centers between the trusses.

The roof ridge is vented and the gable ends have louvered vents, there is no ventilated soffiit construction. I anticipate passive venting of the attic but will consider power ventilation if needed for humidity and heat control.

I originally intended to use fiberglass batt or blown-in insulation and finish the interior with a white metal panel over a vapor barrier secured to the bottom of the purlins. Last week I found a very cheap source of used 1.25 inch polyiso insulation board with foil facing on both sides. I bought 160 4x8 sheets for a dollar a sheet. The material is in like new condition except for a few 1/8 inch holes where it was secured to the original substrate.

I am thinking of installing 9/16" OSB board with foil facing toward the finished room on top of the purlins. This would suffice as a vapor barrier and could provide some reflectance of light if left exposed. I considered using 5/8" drywall (FF one side) in lieu of the OSB board but it provides little in the way of support and I was concerned about the possible deterioation from roof leaks and other sources moisture, so I am leaning towards using the OSB board at this point.

I anticipate installing the polyiso insulation board in two or possibly three layers over the OSB surface in the attic. The board would be secured with 4 inch or longer screws thru the OSB into the top of the purlins, so there will be no exposed fasteners showing at the bottom side of the OSB FF. I also have a source for the required screws at a very reasonable price.

This method of insulating would allow me to have the ceiling construction with exposed wood purlins/FF OSB and install a metal panel ceiling at the bottom of purlins at a later date when more funds become available.

Does any one have any advice or concerns with what I am proposing to do? Any better ideas? Have I forgotten anything?

 

[KennyG]

There are about a million ways to do this, but I will give you my perspective. I'm in the process of renovating an older pole barn essentially the same size as yours. I'm layering up 5 inches of used polyiso in the walls. It's great stuff. I have the advantage of having trusses on 4 foot centers so I'm putting up a 4 mil vapor barrier on the ceiling, followed by metal liner panel directly attached to the trusses. I'm going to lay all my leftover polyiso panels and scraps on top of the vapor barrier, then blow in celulose over it to bring it up to 6" or more.

My first concern with your options is the OSB. Some people like OSB but I don't. It's pretty heavy to add to the truss system when you already have the 2x6 purlins. Also, don't count on foil backing to be a decent reflective surface for lighting. I've seen this arrangement and white liner panel doubles the effectiveness of the lighting.

I'm still thinking my approach makes sense. Vapor barrier, metal liner ceiling, lay in the polyiso and blow a little cellulose to fill in what's left.

 

[BeezFun]

Do you know the spec for dead load allowed on the bottom chord? The live load figure is for things that aren't permanent. If you don't have those specs I'd contact the truss manufacturer because you're adding quite a bit of weight if you go with OSB plus purlins and insulation. I understand why you don't want to go with drywall because of potential leaks. Have you considered ceiling tiles? They're lightweight, white color reflects the light well, easy to fix if you do get a leak, good acoustics in the barn just in case you want to sing. Ceiling tiles are spec'd to take roll insulation run perpendicular to the cross Ts, but I'm not aware of any that can take blown or poured insulation. You could research that.

Getting the vapor barrier right is tough, particularly since your region gets cold in winter and hot/humid in summer. But it's a barn so I wouldn't get too serious about it. If you really want the thing to be comfortable you should put up visqueen on the ceiling to prevent air infiltration. That would also be a very good vapor barrier. If you use roll insulation, the paper backing is sufficient. I think the ventilation you describe in the attic is sufficient to prevent problems, unless you have some large source of moisture coming up from below like from animals or some kind of manufacturing activity. If it's just you out there having fun, I wouldn't worry about it.

 

[TC65023]

Sorry, I meant to say the lower chord of the truss was designed with a 5 pound DL, not LL.

 

[TC65023]

KennyG: I agree with you, OSB in not one of my favorite building materials either, it's heavy and not dimensionally as stable as other sheathing materials. It just seemed to be the best economical solution available to provide some fire resistance material under the polyiso insulation. My insurance company is very insistent that foam insulation materials have a fire barrier like drywall or plywood installed on the conditioned side(if the issue is not addressed properly, they won't insure the structure). The material also would provide a surface I could walk over without falling thru from above and the OSB foil facing would reflect heat back to the interior and at the same time provide a integal vapor barrier.

Your comments about the light reflectiveness of the OSB FF are right on, I was only considering leaving it exposed temporarily until I could afford to purchase and install a white metal ceiling panel system.

I like your idea of installing the polyiso insulation and covering it with blown insulation.

I'm now thinking about installing metal ceiling panel over OSB FF at the bottom of the purlins. Then ripping all my insulation into 22.5" widths and layering it between the purlins and covering with blown insulation. This would utilize the 5.5 inch depth of the purlins, would provide a higher R value and would seal up the system tight. It would also eliminate the need to use long screws to secure the polyiso insulation, a definate plus.

I am interested in additional information regarding your layering of the polyiso in your exterior walls. I want to do something similar but I have to address the issue of the already installed fiberglass condensate blankets with some passive ventilation between the insulation types. I am thinking about vertical 2X4s at 2'-0 O.C.(3.5 inch side against the horzontal girts). Have you installed the materials directly to the horizontal girts on the wall or done something else? How do you plan on covering the insulation at the conditioned side? I have to provide a fire barrier material at the walls too, so I plan to install vertical metal panels over OSB FFl over the layered polyiso.

 

[Smallplot]

What about some of the spray type expanding foams. I hear they have some that when cured are safe to walk on. I also heard it is almost as economical as Fiberglas insulation. With the expanding insulations I think they are getting some pretty good fire retardant values also.

I know you were in MO and I live close to MO. Here is a local company for us that could answer any questions about their products if interested.

Best Systems Builders / Foam Insulators

 

[TC65023]

Concerns about the weight of the added 2X6 purlins and the OSB are valid. I did a quick calculation of both materials per SF, the purlins are 1 pound/SF and the OSB is 2.5 pounds/SF. By the time I add the insulation, metal liner panel, lights /conduit and duct work, I will be over the 5 pound DL allowable for the bottom chord of the truss.

Based on my insurance companies stipulation concerning barrier requirements for foam insulation, I think I need eliminate use of the material in the ceiling construction of my building. Looks like KennyGs recommended white metal panel over vapor barrier secured to the bottom of the 2X6 at 2 foot O.C is the right method in my situation. Un-faced roll insulation or blown-in in the attic between the purlins, seems to be my only DIY alternative.

 

[TC65023]

Smallplot: thanks for your comments about sprayed foam insulation systems. I personally have baggage when it comes to sprayed insulation systems.

I worked a number of years in a facilities management position for a state university in the 80s. My experiences during that time with sprayed insulation contractors was numerous and generally poor. The quality control of the product was horrible and most of the contractors were unreliable.

The crowning blow was when my first new car which had less than a thousand miles on the odometer got sprayed by one of these idiots. It was parked in a lot almost a half a block away from the job site. I had to sue the guy to get a remedy. It was a bad situation to say the least!

I'm sure times have changed but I'm a old guy and refuse to be screwed over again the second time around.

I'm really looking for a DIY solution to my insulation needs since I am retired and have the time to do it.

 

[Smallplot]

:drink: here is to being set in our ways. I understand. I really need glasses, I keep missing parts of posts. You are in the right place for top notch round table discussions. :thumbsup:

 

[Smallplot]

Another suggestion, depending on how your shed is laid out and if you need the entire space utilized. If the reason you are wanting the insulation is mainly for heating, could you build a room inside the shed, say half the shed for instance? You could add ceiling rafters level with the bottom of your existing rafters, and just heat that portion?

If all the space is needed, you could do this throughout the entire ceiling. May have to add a header, or two, underneath to support the added joists. Doing this would give you the load limit you need.