Dear Pole Barn Guru: Ventilation for an Old Pole Barn?

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to:

DEAR POLE BARN GURU: I am getting ready to insulate and heat an older pole barn so I have signed up here for some help and advice. So, I have an older pole barn that really has no eave/soffit vents or ridge vents. It’s pretty crude built. I want to insulate and add a ceiling. My concern is condensation in the attic after insulating. I plan on adding some sort of full ridge vent. Then I need some eave venting or add gable vents. The idea of adding gable vents makes me nervous because I don’t know how to seal them properly with the ribs in the metal siding. I will attach pics. Is there a way I can build in some eave vents? The metal roof just comes down the sides of the barn and there is an air gap between the rood and the siding that is covered by the white trim/flashing as seen in the pictures. Any ideas on what to do with this old barn before I start finishing it would be a big help. I also thought about attic fans in the ceiling. CB MAN

DEAR CB: You asked for advice, so here it is….your old building has some challenges when it comes to attempting to heat. The ventilation issue is just one of many. The building has no insulated vapor barrier under the roof steel to prevent condensation, which you have touched upon. Two other factors, either of which could be deal breakers – the building has horizontal sliding doors, which are impossible to properly insulate and seal, without them becoming permanently affixed, and the roof trusses are probably not designed to support the weight of a ceiling.

With all of this said, you have two really good solutions – the least expensive is to just put up another new pole building, designed properly to be climate controlled, using your existing building for cold storage. The other – knock this building to the ground and rebuild at the same location.

Assuming you may not be interested in either of these, and want to pour lots of money into a building you refer to as “crude built”; I will give you some solutions.

Toughest first – the trusses. As they are prefabricated wood roof trusses, there should be a manufacturers stamp on every truss. The design loadings might be stamped on the trusses (due to the age of your building the “might” is the operative word). With this information and the location of your building, I could probably give you an idea as to adequacy. If the truss manufacturer’s name can be found – see if they are still in business. If so, they can determine adequacy for you (for a small fee) and get an engineered repair if they are not adequate. If those fail, hire a registered engineer to do an evaluation for you.

Condensation under the roof steel…as the steel is nailed on, it cannot be removed and an insulated vapor barrier (something like A1V reflective insulation available from added. The best solution is probably going to be to spray foam insulate the underside of the roof steel.

Adding a ceiling – with the trusses verified for the ability to take the load (and correctively upgraded if needed), 2×4 ceiling joists can be placed between the bottom chords every two feet, with LU24 or similar joist hangers at each end.

Screw on 5/8” Type X gypsum board to the underside of the ceiling joists and trusses (it won’t span four feet, so don’t even attempt to). Leave an attic access hole somewhere close to the center, so insulators can blow in the desired thickness of insulation. Do NOT place a vapor barrier between the ceiling drywall and the framing above.

Ventilation – the new codes do not allow for gable vents to be mixed with eave and ridge vents. It is…use one or the other. Take the square footage of the footprint of your building, and divide by 300. This gives the net square inches of ventilating area which must be provided in each gable end of the attic. Hansen Pole Buildings has vinyl gable vents, in a myriad of colors, with snap rings. A hole is cut in the steel (using the snap ring as a template), the vent is pushed through from the inside, and the snap ring is then pushed on from the outside (this is a two person job). These vents are designed to accommodate ribs on steel panels.

Now the roof is taken care of, the walls are the next challenge. Remove the sliding doors and frame the openings down in size to fit insulated steel sectional overhead doors. You may be able to salvage the steel off the sliding doors, and if done carefully, use the pieces to fill in the gaps.

Again, the nailed on wall steel becomes a limiting factor….spray foam for the walls is probably the best solution. Keep in mind, you will need to put either drywall or a steel liner panel on the inside of the columns, as Code does not allow spray foam to be left exposed to heated areas.

Good luck – and let me know what choice you make and how it turns out.

DEAR POLE BARN GURU: We just made a phone call to Menard’s to order over a hundred bags of blown-in cellulose. While talking to the guy in the building department, he asked if this is for a pole barn, Told him yep. He then strongly emphasized to NOT use blown-in cellulose above the metal ceiling because the flame retardant material will rust and eat up the ceiling. This is the first I have heard of, so I did some quick research online and it looks like they have some kind of acid that act as a flame retardant.

Right now, our 30×48 gambrel pole barn with loft are being built. The shop will be finished with R-19 fiberglass in the walls and then T1-11 panelings will be installed. The ceiling is going to be a metal liner, obviously. The loft will be used for storage and man cave, so half of the loft would be finished in the future. There will be Low-E condensation barrier below the roofing, so the contractor told us there is no need for a vapor barrier in the shop ceiling where I would be blowing the cellulose.

Right now I am not sure what to think. Several months ago I did some research and have decided to plan on blown-in cellulose. Is this something I should be concerned about? What should I do to avoid the rusting issue the guy told me about? BTW, he told me to instead use blown in fiberglass which is something I am not thrilled about. Thanks. PERPLEXED

DEAR PERPLEXED: If the fiberglass and cellulose insulation people would spend more time promoting what each of them do as good, and less time shooting broadsides at each other, life would be so much better and they would probably each sell more product.

There have always been concerns about insulation causing corrosion when in direct contact with metal building components such as sweaty pipes, electrical wires or metal boxes, etc. Consequently, ASTM (American Society for Testing and Materials) standards for every insulation material contain testing which specifically addresses these concerns. In addition, in 1979, the CPSC (Consumer Product Safety Commission) promulgated a law, which regulated the fire and corrosive characteristics of cellulose insulation. A statement of compliance with these requirements is required on every bag of cellulose insulation. The types of metal tested with all insulation materials are copper, aluminum, steel, and additionally in Canada, galvanized steel. The test requires placing soaking-wet cellulose insulation with an imbedded .003-inch thick metal coupon inside a humidity chamber under conditions that are ideal for promoting corrosion. After 14 days, the metal coupons are removed, cleaned, and examined under a light to detect the smallest pinhole. In all, there are two coupons of each metal and all must be free of even one pinhole. This is a very strict test!

My recommendations are to make sure your attic area is adequately vented (no less than 1/300th of the attic footprint area in venting, provided at least ½ of the vent area is in the top ½ of the attic), make sure the insulation stays dry (no roof leaks), and do not have a vapor barrier between the ceiling and the insulation. Whether you choose fiberglass or cellulose, either should be fine.

2 thoughts on “Dear Pole Barn Guru: Ventilation for an Old Pole Barn?

  1. I getting condersable amount of condensation inside my pole building. The walls are insulated with 4×8 sheets of insulation board. The ceiling is insulated with fiberglass roll insulation. The attic has soffit vents all the way around. Do I need more ventalation in the attic or should i install a ventalation fan in the main area.

    1. admin Post author

      Start with looking to the source – which is most probably the concrete slab. If you lay a wrench on the slab one day, then return the next day, pickup the wrench and there is a dark spot where the wrench was, then your floor does not have an adequate vapor barrier underneath. If this is your case, the floor needs to be sealed.

      Next – if you do not have a vented ridge, you need one.

      Make sure the eave intake vents are not blocked by the fiberglass batts, you should have no less than an inch of clear area above the batts at all times.


Leave a Reply

Your email address will not be published. Required fields are marked *