condensation and humidity in pole barn

[midwestman23]

Still trying to learn as much as I can before we sign our contract to build our pole barn/GYM. It is still clear as mud to me what final plans we should do in our build. Long story short IF we heat I think it will be situational heating to add to the comfort for a day. My thought is wouldnt the barn be like a can of soda. If you take it out of the fridge and it is in heat then it will sweat and bead up with water. Wont the barn do the same thing if I dont constantly heat it? Any help with this ?? Is that what the vapor barrier helps with? Just trying to figure if we should insulate and line the building even if we dont plan on heating it all that often as it will be too large of space for us to afford to heat often.

 

[stm317]

Condensation forms when warm, humid air contacts a cooler surface. You need humidity, and a fairly significant temperature difference or you won't have any condensation.
On a winter day, your exterior metal will be cold. Adding heat will increase humidity in the air inside the building (the type of heat will determine just how much humidity). If the warm air contacts the cool metal, you'll get condensation. We prevent this primarily by properly insulating and preventing the warm air from contacting the cooler surface. A moisture barrier, which is semi-permeable (such as Tyvek) under your exterior metal will keep the bulk of the moisture that's outside from getting into your building. A true vapor barrier, which is IMpermeable to moisture vapor should typically be placed on the inside of the insulation for a building that will be heated. Insulation fits in between the two barriers.
Typical insulation* cannot do anything about moisture movement, so the idea is to limit and control the moisture before it gets to the insulation, and allow whatever moisture does get there to dry to the outside.

So, the general idea is a 2 part approach. The vapor barrier should prevent all of the moisture that exists naturally in the heated inside air from making it's way into the wall cavity (where it would move freely to the exterior metal and condense). And the insulation reduces the temperature difference between the inside air and the exterior surface of the building, which makes condensation less likely.

*Closed cell spray foam, when applied a couple of inches thick, can be an impermeable vapor barrier. If you use closed cell spray foam, then no additional vapor barrier should be used.

 

[Lonnies Performance]

Moisture isn't introduced by heating unless the actual burning of fuel takes place in the building... such as a torpedo heater. A burner that takes air from outside & is vented outside will not add moisture. As long as the building is warmer than outside, the internal humidity should be lower. Keep in mind, that a frozen car thawing in the building or anything wet will contribute to the humidity problem.

You can also periodically heat with a torpedo heater as long as you open all doors to blow in the cold dry air displacing the warm moist air in the building every night instead of letting the closed building cool off & therefore condensing moisture.

I did this last winter as I was working without a permanent heat source. 1 gallon of kerosene adds about 1 gal of moisture to the area.

 

[Showkey]

Your correct to be concerned about humidity and condensation. It’s one of the reasons to consider stick build vs a metal building.

If your going to control humidity and condensation you must have complete control of the building’s climate and the building must be insulated.

 

[MagKarl]

Or...adequately ventilate the space and condensation will also be minimized. I have 24" overhangs with vented soffits and full ridge vent. No condensation troubles with the building itself, but I do still get some dew on heavy machines like my tractor that warm up much more slowly than the air does.

 

[matt_i]

My 0.002 is this. One of the classic issues with a post frame metal skin building is condensation occurring on the underside of the roof and raining down inside of the shop if conditions are just right. I would counter this by using plywood or osb instead of roof purlins, then sheet this with synthetic underlayment that's designed to go under metal (extra hot temps can result). But now you have a control for the moisture no matter what else you do.

To further the adventure, I would build a ceiling and hang some sort of a covering whether it be metal or drywall or osb/ply. Then insulate above it and vent the attic from sofft to ridge.

Insulate the walls, spray or batts and cover.

Now you have a space to trap heated air, which you will produce with a Vented heater. The more you keep it closed, the less humidity will affect you.

And last, get at least one ceiling fan, keep it on lowest speed 24 x 365. Moving air does not allow moisture to condense as easily. In my opinion its the best bang for the buck.

 

[midwestman23]

STM- With how your describing it even if insulated the metal liner on the inside of the building will still be cold im sure during the cold months since it wont be heated 24/7. When I do heat it on certain days then wont the liner of the building bead up with moisture then? Do I just run a dehumidifier or is it not that big of deal? Also my builder said tyvek is not needed but a 6mil vapor barrier is and will be installed?

 

[midwestman23]

Thanks for the info Lonnie....It would be a radiant heat I think from LP tank on the outside
Showkey- was just advised on pole building for the height I am doing with 18ft sidewalls?
MagKarl-Is your building insulated and if so how? just curious...

I currently have 1 ft overhangs on the entire building how much more beneficial would it be to make them 2 ft?

 

[midwestman23]

Matt-Thanks for your 2 cents. ALL of the advice and help is HUGE to us! We would have a ceiling with r30 I believe blown in insulation and a vapor barrier. We will have a metal liner on the ceiling as well. There will be soffit and ridge vents as well. I agree on the fan piece and appreciate that. Just trying to understand things before the build. We definitely wont heat the space daily as it will be too large of a structure but want to when we have a good reason to. Just was worried if its 25 degrees in there then we blast it with heat what the result will be??!

 

[Showkey]

If your going to run a dehumidifier...........the building must be insulated and sealed, have a low air exchange rate and have Climate that is controlled. Without the above the dehumidifier will not be effective and will not work in lower temps and very expensive to run in large space.

 

[midwestman23]

ok thanks! no de humidifier!

 

[stm317]

STM- With how your describing it even if insulated the metal liner on the inside of the building will still be cold im sure during the cold months since it wont be heated 24/7. When I do heat it on certain days then wont the liner of the building bead up with moisture then? Do I just run a dehumidifier or is it not that big of deal? Also my builder said tyvek is not needed but a 6mil vapor barrier is and will be installed?

It's possible for condensation to form on the inner wall material, but less likely. There's not a ton of moisture in cold air, so it's harder to condense to begin with. Keeping the air circulating with a fan will help too.

If you're going to be using fiberglass or cellulose insulation, I'd strongly suggest a moisture barrier Between the insulation and the siding. Insulation loses efficiency when it gets wet, even just humid. And it struggles to insulate well when air moves through it. Having a moisture barrier in place will reduce both moisture intrusion and wind coming through the metal, which lets your insulation focus on it's primary job. If your outermost insulation is foam, then moisture intrusion and air movement are less of an issue and you might be ok to skip the Tyvek.

 

[Lonnies Performance]

Thanks for the info Lonnie....It would be a radiant heat I think from LP tank on the outside
Showkey- was just advised on pole building for the height I am doing with 18ft sidewalls?
MagKarl-Is your building insulated and if so how? just curious...

I currently have 1 ft overhangs on the entire building how much more beneficial would it be to make them 2 ft?

My steel building is a shallow pitch roof with 15'walls & 18' in the center.
with 8" white faced insulation. No overhangs.

I would warm it with a torpedo & the next morning when it was very cold (single digits), you could see ice dots on the floor below all the roof screws in the center of the building as it cooled off. Typically a dehumidifier removed a lot of moisture, but did not work well until you got it over 50 deg.

The radiant heat should serve you well.

For summer I do not have any condensation, but in the dead of summer it was humid in the garage as it was much cooler inside than outside. After I saw how much energy a dehumidifier used, I realized it was better to air condition the place to remove the humidity. I'd rather be cool & dry than just dry. My dehumidifiers each drew 8A at 120V, so basically 960 watts times 3 for power. I had 3 of these running this spring & though they caught a lot of water, they quickly heated up the building also. Conversely, 2 split systems in the building, on a 80+ deg day, each drew 3.25A at 240V (1560W total) while maintaining a 72 deg temp.