Metal Roof Condensation Prevention Question

[brown40]

I don't know how tight or expansive your building is, but it may be using a power ventilator can get your inside and outside air temperatures close enough that you don't hit the dew point, as well as keep things moving around... just like the car windshield, moving air doesn't tend to condense as readily. It'd be a real easy solution (if it works) that you could transfer to the new garage when the time comes.
Insulating would hinder the heat transfer, but would be tough to re-use, and would be perforated in areas. There's a bunch of sites with formulas for determining building air exchange, as well as sizing ventilators and establishing the square inches of eave--> ridge/gable vent you need to exchange the building naturally in a given time. Where you've got an established problem, I'd err on the high side for CFM's and have a vent blocking plan for winter if you plan to heat the space. Just a thought...

 

[M E Cook]

I doubt it. Condensation forms when the outside temperature lowers the inside temperature to the point of 100 percent humidty on the surface of the metal. In humid climates, this happens almost every morning from Spring to Fall. You need enough of a barrier to prevent those temperature changes from happening.

Insulation is the easiest way to do this, and spray foam is probably the best. You want closed cell foam,which is about twice as much as open cell foam. Open cell foam absorbs and holds moisture, so over time, there will be a small amount of condensation that forms between the bottom of the metal and the top of the foam. This moisture will build up inside the open cell foam and eventually lead to mold and decay of the foam. It will also cause the metal to rust.

I have a 24x36 pole barn side are insulated with rigid foam and lined with osb I was thinking about puting holes with screens in the 2x6 between trusses at top of wall. I have ridge vent length of building and put gable end vents then blowing in insulation after putting in ceiling !! my question is do you think I will have condesation problem with this method? in tennessee humid in the summer thanks Mike

 

[EddieWalker]

I have a 24x36 pole barn side are insulated with rigid foam and lined with osb I was thinking about puting holes with screens in the 2x6 between trusses at top of wall. I have ridge vent length of building and put gable end vents then blowing in insulation after putting in ceiling !! my question is do you think I will have condesation problem with this method? in tennessee humid in the summer thanks Mike

My shop is very similar in size and the humidity is pretty extreme here. I have insulated walls and an open ridge vent. I get some surface moisture on my ceiling, but not enough to rain inside my shop. I air flow from my eaves to my peak keeps it to a minimum. The only way I know that there is any moisture at all is over time I've developed some staining on my purlins.

One of my goals is to install a metal ceiling to the bottom of my trusses and blow in about two feet of Attic Cat insulation. I feel that with the current air flow that I have, I'll be fine.

When I build my addition, I am going to have an open vaulted ceiling with massive exposed beams and a wood ceiling. Between the ceiling joists and the metal roof, I am planning on using closed cell insulation right up to the metal so there will be NO AIRFLOW. It will just be all one solid mass. I know this is going to be freakishly expensive to do, but feel that the cost is just part of creating the room that I've always wanted.

As to the original poster and his question about his roof. Since you don't have any venting, the closed cell insulation is probably your only solution. An inch is probably all you need. Two would be more then enough, but I would call a couple of insulation companies and have them bid on it. Do not let they talk you into open cell. It's cheaper and easier for them, but it's the wrong product for metal roofs.

Before doing that, running a fan, or several fans might do it to for a lot less money. That was a good idea, and worth trying.

 

[geteh]

Eddie hit the science spot on.

Cold metal, with warm humid air inside is what the cause is. The cold metal cools the air right near the metal below the dew point and the water drops out of the air. Same way a cold beverage sweats.

Only way to prevent is to:
1. Keep the metal warm. Which is not an easy thing.
2. Keep the air right next to the metal cool enough.

To achieve that, as others mentioned, vapor barrier works well. Another solution, which may be easier given the long term plans, is to go ahead and insulate. You can insulate the bottom chords of the trusses, and with proper ventilation, keeps the attic, and air near the metal, at the same temp as the ambient air Metal roofing suppliers. And if the metal and air surrounding it is at the same temp and outside ambient, the only way it will be wet is if it's raining

I’m planning on turning the garage into a workshop and have noticed this winter (we only moved in last year) that the corrugated metal roof seems to gather a lot of condensation. It drips down, not torrentially, but I’d want to sort it out before I get the electricity put in obviously. Having it a bit warmer would be a bonus too, so I was thinking of putting in some framing and insulation board beneath the metal.
Just looking for some advice on what thickness of board is minimum and what space I need to leave between the roof and the board. Then, do I need anything else? Does the whole thing need to be sealed with a vapour barrier? I also wonder whether I need to make sure that the cavity between roof and insulation needs to be totally sealed or if it needs ventilation?
Lots of questions here but I’m sure people have had similar issues so just looking for general advice. I’m trying to keep the job as cheap as I can - and it’s mainly about keeping it dry rather than toasty warm.

 

[bdhsfz6]

My 40' x 30' steel pole barn is used mostly for implement storage and dripping condensation, although annoying, really isn't a big problem.

I do have a workshop in one part of the building and to keep it dry, I screwed cheap corrugated PVC roof panels to the underside of the trusses over the shop area.

Palruf 26 in. x 8 ft. Corrugated PVC Roof Panel in Clear 100423 - The Home Depot

Give your outdoor space the affordable upgrade it needs - meet clear PALRUF corrugated panels. Lightweight and easy to install, these cost-effective, DIY PVC sheets can be used as patio covers, partitions,

www.homedepot.com

I used clear panels so as not to block the light coming through the skylights.

The condensation drips onto the PVC panels and usually just evaporates. On rare occasions, enough builds up and runs along the corrugations into a cheap plastic gutter I mounted on the panel ends.

Not an elegant solution but neither is the building. Problem solved for around $100.

 

[Tinhack]

Humid air is lighter that dry air (believe it or not). When humid air contacts cooler air or objects, it produces condensation. That's how we get rain. It's also the reason "ridge vents" work so well in keeping a barn or building dry. Lacking walls and ridge vent (carport) I think your best course of action is to install a ceiling fan or fans to move air through the carport and directed upward. This would move the cooler air to the ceiling and humid air away or down the walls, if you had any. Purely speculation, of course.

 

[EddieWalker]

I’m planning on turning the garage into a workshop and have noticed this winter (we only moved in last year) that the corrugated metal roof seems to gather a lot of condensation. It drips down, not torrentially, but I’d want to sort it out before I get the electricity put in obviously. Having it a bit warmer would be a bonus too, so I was thinking of putting in some framing and insulation board beneath the metal.
Just looking for some advice on what thickness of board is minimum and what space I need to leave between the roof and the board. Then, do I need anything else? Does the whole thing need to be sealed with a vapour barrier? I also wonder whether I need to make sure that the cavity between roof and insulation needs to be totally sealed or if it needs ventilation?
Lots of questions here but I’m sure people have had similar issues so just looking for general advice. I’m trying to keep the job as cheap as I can - and it’s mainly about keeping it dry rather than toasty warm.

I'm not sure what you mean by "insulation board"

The more air that you have under the metal, the more moisture you will have when the temperature outside reaches dew point in the morning.

If you have plywood touching the metal, and the only air is the space between the high parts of the metal, you will still have condensation, but it will a lot less then before. That moisture needs to have a path to escape. When building new, OSB or Plywood is used, then Roofing Paper, or a Synthetic is used to keep everything dry.

The only way to dry off the inside of the metal is air flow. You need a ridge vent that goes the full length of the building to dry off the moisture. As the air warms, heat rises, and that movement dries off the underside of your roof. Same thing happens with shingled roofs on houses.

Closed cell foam creates a solid seal against the underside of the metal, and that stops all of the moisture. It's expensive, but it's also very good and probably worth the money.

In my opinion, creating a ceiling and installing blown in insulation is the most cost effective way to stop this, and also allow you to heat and cool the space. Metal R Panels will span 4 feet and be strong enough to hold two feet of insulation. Depending on the spacing of your trusses, you might need to add to your framing to do this.

With good air flow, and an insulated ceiling, your moisture issues will go away.

 

[chim]

At work our weld shop had roof leaks even when it wasn't raining. It was difficult to tell whether the water was coming from actual leaks or condensation. The very gently sloped metal roof was about 30' high and around 20-ish years old. There was fiberglass batt insulation on the underside of the roof.

It was discovered that the vapor barrier was damaged / poorly sealed at quite a few locations. Air could get from the occupied space into the insulation. As long as it was cooler outside, there was condensation that would perk down through the insulation. Numerous rust perforations were found, with most being around the roofing fasteners.

The problem was resolved by having a coating of insulation sprayed on the outside of the roof. The insulation used was about 2-3" thick and very hard when cured. Walking on the flexing roof prior to the application felt risky, but following the application it felt much like walking on concrete.

The final step was removing all the batt insulation on the underside of the roof.

 

[CliffordK]

Commercial installed closed cell spray foam would also make an excellent barrier.

 

[chim]

In our case, 0ne benefit of having the coating on the outside of the roof rather than the inside was stopping further degradation of the metal roof. Having the roof covered with a monolithic seal put the metal roof on the warm and dry side of the insulation. This was particularly attractive because there were already rust perforations of the metal roof.

With spray insulation on the inside there was concern that even if the rust-throughs were patched, the patches could fail or other holes could appear. Then rain water would get between the metal and the insulation.