Pole Barn Condensation

UP Oliver

Member
Thanks to everyone for their advice/help with regard to the questions I have about my upcoming pole building. I really appreciate all the responses.

I thought I should let everyone who is interested know what my plan is for condensation control outside of putting something on the inside of the metal roof.

I am taking all the topsoil off and plan to fill it in with sand. That will probably be around 12 to 15 inches of sand. Then finish it off with some gravel except where the 20 x 40 piece of concrete will be. I was planning to have vented soffits and a ridge vent to get as much air through as possible. I'm wondering if I need anything up against that metal at all after reading some of the posts. We get most of our wind from the northwest and there will be at least a quarter mile of open space in that direction. I would guess I will have great ventilation, which is said to be important, and I would hope the sand and gravel will keep the moisture to a minimum at the floor level. The ground will slope away on all sides when I am done. Any thoughts?

Thanks again.
 
Put a barrier between the sand and the stone. If none the sand will migrate to the surface and make trouble. I would choose #6 and larger lime stone or crushed granite for 10 inches then road base to top it off. Jim
 
Sounds like a plan. Not a bad idea to vapor barrier the floor. I know when we pour concrete down here we always put a 3mil plastic between the cushion sand and concrete to reduce the opportunity for sweating on humid weather changing days, especially for occupied dwellings.

Mark
 
If you are doing all that grading, roll out a plastic vapor barrier, so ground moisture doesn't wick it's way upward. It don't cost much!
 
Soffit venting!

The first barn I put on my place was a corrugated sheet metal structured pole barn. At the top of the poles I put 2 ea. 2x6's, one inside and one outside to put the 3/12 trusses on.

I ran the wall tin up to the top of the 2x6's leaving a gap between it and the underside of the roof the height of the trusses at that point which was about 5-6 inches. I thought that this would be a real neat vent and keep the barn cool and dry. Ha!

The roof sheet metal extended past the the side of the barn 12" (overhang).

Not long after I built it a thunderstorm rolled in with moderate winds and heavy rain. I was standing inside about 3' from the wall GETTING SOPPING WET!!!!! When it stopped, I boarded up the open spaces (vents) between the trusses.

Point here is that you have to do something with your roof water to keep the wind from blowing it into the barn. Gutters is a solution as would be to build the soffit like a brick house where you close it in and put your vents on the under side of the soffit.

Forgot about that in my earlier reply.

Mark
 
I don't think it would help that much to rework the ground. I have a building with a concrete floor that is fully insulated with the exception of some R-panel fiberglass skylight panels. There are many days condensation drips from the fiberglass panels. I know if the ceiling wasn't insulated the building would drip as bad as another building I have with a dirt floor.
 
When I had my barn built by a company from Michigan, they told me the price for 35 year shingles and trusses on 2 ft was the same as metal. For me, growing up on a dairy farm and seeing all the condensation formed on the inside of the metal roof, it was a no brainer, 35 year shingles.

The cows stayed in the pole barn, it was 3 sided, opened on the south. In the winter all the condensation, mostly produced by the cows, was frozen on the inside of the barn. When the sun came out, it rained.

Check it out and see what the price difference is. I have replace insurance. Get a good hail storm every 12-20 years, so my insurance company replaces my shingles before they go bad.
George
 
In answer to your question: Bare Metal. No insulation whatsoever. I would not do a thing differently. My soil conditions-sandy, well drained- are such that a moisture barrier under the floor is simply not needed. My floor is completely concreted (60x88). Black roof is highly recommended for roof warmth in your neck of the woods. With high sides the roof will be up where it will not be too hot at the ground level with the doors open. Soffit vents should be on the underside of the overhang (2' overhang recommended). Full length ridge vent. Make sure trusses are spaced properly for snowload. I get no condensation and bare metal parts of machinery (disc blades, coulters, etc.) stay shiney.
I also have 10 skylights. No need for any lights during daylight hours, even with the doors closed. And no, the skylights do not leak.
And, I have wainscoating at the bottom all the way around to avoid having to replace long sheets of metal but so far no one has driven into it and no ice has caved it in. With a black metal roof, once the snow starts to slide off, it really slides and lands out some distance from the building. Not so with a shingled roof. I wouldn't even consider a shingled roof. Put your entrance doors on the ends to avoid the snow blocking them. Also from hitting you on the head.
 
Reading your post, you may want to reconsider the use of sand under a slab on grade. While its well drained, it can be difficult or impossible to get optimum compaction because the fines or small aggregate is all the same size, you need a composite material such as gravel, which has an array of sieve size aggregate, along with optimum moisture to obtain suitable compaction. Ideally you want to excavate all topsoil, organics out, to undisturbed, suitable bearing soil, then build up the sub base in 12" lifts compacted 95% or better, so that it does not settle under the slab.

Even where there is no slab, you may not get the stability you need or expect, I'd just build it up with crusher run, run of bank gravel, or similar, it would likely perform as you need, instead of displacing. Under a roof, that sand will likely dry out and even if you had optimum moisture when placed, and it did compact, when it drys it could be like driving on sugar.
 
When we built the barn in Dallas, discovered condensation had run down the metal roof to the purlins, then dripped on the hay. Ruined about 14 small squares.

I bought a bunch of terry cloth (what towels are made from) and attached to the purlins where they touched the roof.

Condensation would run down the metal roofing to the purlins where it was absorbed by the terry cloth. That ended the dripping problem.

Attaching it wasn't hard since the area was full almost to the roof with hay and I could stand on the hay and easily reach the purlins.
 
Your decision for your project...but I will NEVER build another metal building without insulating the underside of the roof. That insulation might be the thin fiberglass batt covered by plastic or it might be OSB sheathing covered with tarpaper. But where I am, if you do nothing to insulate the metal roof from the interior, you will sometimes get condensation that RAINS inside the building. The moisture is in the air. It even rains sometimes in a fully open hay shed.

Maybe your conditions are different, but I would advise insulating beneath the roof metal. It doesn"t cost that much, and although it is a little bit of hassle to install, now is the time to do it. Then you will not wish you had insulated sometime later and be thinking about removing the tin to RETROFIT the insulation. Good luck!

And a question I have for one of the posters: where do you get black sheet metal? I have never seen any for sale or on any buildings around here. We usually pick white or galvanized for roofs to try to reflect some solar heat gain. I bet it would get very hot under a black roof.
 
Any major building manufacturer offers multiple colors for roofing, siding, wainscoating and trim and have a "color a building" feature in their website. Morton, Walters, also Cleary. Try them. And, no, black doesn't get too hot if the roof is high enough and you have the good sense to open the doors in the summer time. And it surely does work nice in the winter. And, oh yes, I don't give a rip whether you like it or not.
 

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