Metal roofs and condensation

[Howard E]

Thought I would share this for those contemplating building a coop or house, and it relates to moisture and condensation within a house.

We had rain and some wet snow yesterday, but towards dusk, all that blew out and it became a calm, clear night. Temps in upper 20's. Woke this morning to fog and a heavy frost.

When I went out to do chores this morning, this is what I found INSIDE my barn:



That was several lines of water that had dripped off the uninsulated metal roof. Found these water drops on an old wooden bench. That could just as well have been one of the birds if they were roosting under the drip line. BTW, there was nothing in the shed. With livestock in there, those drips turn to rain. Not good when things you have stored in there....things you want to keep dry......like hay, feed, etc. are getting wet INSIDE your building.



By comparison, I left home to go to my daughter's place and she has a nearly identical barn, except hers has insulation between the metal roof panels and and interior of the shed. Her barn had no water spots at all. Bone dry.



This was also addressed in one of the old poultry books I use for a reference:




Keep in mind, this was from 100 years ago. The concept of using a bare metal roof and the problems associated with it remain, but other solutions are possible, such as that layer of insulation between the metal roof and interior. Birds will peck at and eat insulation, so if they are able to reach it, probably best to cover it or use something other than metal roofs.

But bottom line is bare metal roofs over a chicken house (or just about any other shed) is going to cause trouble. The reason mine is not insulated is the guy who built it opted for size over quality, so built a large, inexpensive building. He saved on the cost of the insulation and I'm now paying the price.

 

[KettermanHillCoop]

Question: If your roof is plywood...then...covered with corrugated roof panels, will that prevent the "raining" inside the coop? Would the plywood act like the insulation?

 

[Howard E]

Probably. My Woods house has regular composite shingles over plywood and I get no condensation in there, but it is also a Woods house. Meaning wide open ventilation.If you go this route, you will also want to have wide open ventilation if at all possible.

Do much research and there are basically three things needed to prevent condensation in buildings.

1. Reduce the moisture level inside. (Good luck with that if you raise chickens and keep water inside, have a high population of birds inside and/or use deep litter over dirt floors. That is a high moisture environment).

2. Vent moisture to the outside. Wide open ventilation does that......moisture has an escape route to flow out, vs. having to condense out. Ventilation also tends to equalize both the moisture and temperature levels inside and out. In what seems like a contradiction, warm moist air...the culprit of condensation.....rises and flows out....as if it is on a conveyor..... if you have good ventilation that allows it.

3. Principle of insulation is to isolate any warm moist air inside from cold metal roof, siding or or other surfaces on the outside. Works like putting an insulation sock on a cold beer in summer. Insulation limits access of the warm moist air to the cold surface of the can, and water does not condense on the insulation. Concern here is if warm moist air on the inside of the building contacts cold surface, it may still condense, but then be trapped between the two as liquid. Rot, mold, etc. follows. You may not see it, but it is there just the same. So best practices would leave an air gap between the two to vent any air and condensate moisture out.

If you really want to use a metal roof, and I might if I was to do the Woods house again, I would opt for hard insulation board under it. The polyiso foil faced stuff. White inside, shiny aluminum side up facing roof. Rafters, with purlins running crosswise over those. That is how my daughters barn was done.

Instead of the hard foam, many commercial pole barn builders install a layer of bubble wrap over the purlins.......loosely to let it breath.....them metal roof over those. This type of bubble wrap is white on the inside and shiny reflective foil on the outside, facing the metal roof.

BTW, white or light colored metal roof is cooler than dark.

 

[KettermanHillCoop]

Probably. My Woods house has regular composite shingles over plywood and I get no condensation in there, but it is also a Woods house. Meaning wide open ventilation.If you go this route, you will also want to have wide open ventilation if at all possible.

Do much research and there are basically three things needed to prevent condensation in buildings.

1. Reduce the moisture level inside. (Good luck with that if you raise chickens and keep water inside, have a high population of birds inside and/or use deep litter over dirt floors. That is a high moisture environment).

2. Vent moisture to the outside. Wide open ventilation does that......moisture has an escape route to flow out, vs. having to condense out. Ventilation also tends to equalize both the moisture and temperature levels inside and out. In what seems like a contradiction, warm moist air...the culprit of condensation.....rises and flows out....as if it is on a conveyor..... if you have good ventilation that allows it.

3. Principle of insulation is to isolate any warm moist air inside from cold metal roof, siding or or other surfaces on the outside. Works like putting an insulation sock on a cold beer in summer. Insulation limits access of the warm moist air to the cold surface of the can, and water does not condense on the insulation. Concern here is if warm moist air on the inside of the building contacts cold surface, it may still condense, but then be trapped between the two as liquid. Rot, mold, etc. follows. You may not see it, but it is there just the same. So best practices would leave an air gap between the two to vent any air and condensate moisture out.

If you really want to use a metal roof, and I might if I was to do the Woods house again, I would opt for hard insulation board under it. The polyiso foil faced stuff. White inside, shiny aluminum side up facing roof. Rafters, with purlins running crosswise over those. That is how my daughters barn was done.

Instead of the hard foam, many commercial pole barn builders install a layer of bubble wrap over the purlins.......loosely to let it breath.....them metal roof over those. This type of bubble wrap is white on the inside and shiny reflective foil on the outside, facing the metal roof.

BTW, white or light colored metal roof is cooler than dark.

Yes, I'm planning a Wood's house. Not set on size yet.

House will sit where current coop is, adjacent to the existing 10'W x 10' L x 6'H (chain link dog kennel) run. The run has red corrugated roof panels.

Location of coop is set back about 20 ft into the south-facing tree line of the woods. Plenty of shade.

I'm definitely going with corrugated metal roofing as the other 8 buildings on the property have metal roofing.

What are your thoughts on coating the plywood with Blackjack 57 prior to attaching metal panels? Would that prevent rot? Being the metal panels are corrugated, wouldn't that allow air flow between the plywood and metal panel...to some degree?

I'm already going to be purchasing Blackjack 57 for the interior so another 5 gallons wouldn't be a big deal... Aside from the aesthetics of matching the other outbuildings, the shingles, tar paper and hardware will be quite the jump in my over-all cost factor.

 

[Brahma Chicken5000]

I’m planning to replace a shed roof with corrugated plastic panels and I don’t want it to leak, how can I insulate the roof? The shed is going to be converted into a henhouse.

 

[Howard E]

For a poly / plastic type roof, I wouldn't worry about insulation, nor condensation. I did that on the front part.....what is called the "scratch shed" of my Woods house and I get no condensation there. I used the opaque stuff, which lets in about 80% of the light. So not direct sunlight, but certainly light and bright. Part of the reason there is no condensation with the poly stuff is there is no latent lag time when it is colder than the surrounding air.

Conditions that often result in condensation in my shed.....the one in the first post.... are periods of extreme cold, followed by a sudden warmup. My folks have a metal machine shed that is worse. Heavy steel beams support a flat roof on top. Those beams get ice cold, then a sudden warmup follows.....in the early morning hours.....often 90%+ humidity levels in the air........and inside that shed, humidity starts to condense on those beams. So much so it forms droplets that eventually fall off. It rains inside.

Put birds in a building........their warm, moist breath.....moist droppings.......moisture working up from deep litter from below.......it gets humid in there and that will easily condense out on cool metal roof. Rather than being an isolated now and then type of thing as with my horse barn, or my folks shed, it happens often.

Having thought about this, I still think you would be ahead to use the hard polyiso board instead of plywood. Insulation plus vapor barrier. Cost is about the same, with no rot issues. Birds will peck at hard insulation boards, but birds should not have access to insulation under the roof.

And if you use insulation board, house will be cooler in summer. Doubly so if you use anything but a white/light colored roof.

BTW, if you live in USDA Zone 6 or colder......basically winter temps to -10F to -15F or colder, and you are using metal siding, I might consider insulating the sides too. That creates its on set of problems, but I'd do it just the same. Even with a wide open Woods Coop.

 

[Brahma Chicken5000]

So I don’t need to insulate corrugated roofing panels?

 

[KettermanHillCoop]

@Howard E

For a poly / plastic type roof, I wouldn't worry about insulation, nor condensation. I did that on the front part.....what is called the "scratch shed" of my Woods house and I get no condensation there. I used the opaque stuff, which lets in about 80% of the light. So not direct sunlight, but certainly light and bright. Part of the reason there is no condensation with the poly stuff is there is no latent lag time when it is colder than the surrounding air.

What are your thoughts on poly / plastic corrugated on the back part as well?

 

[Coopnrun]

I've built many deer stands using metal roofs. These are generally well ventilated, open windows, and with just a person setting in them you will get condensation dripping. My fix has been to attach 1 inch styrofoam under metal which has been pointed out, the chickens will peck. I'm presently building a coop and plan to place a 1/4 inch sheet of plywood over the enclosed area only. Then I have some left over bubble/foil insulation that I will staple to that, then the metal. My thinking the insulation will aid in keeping coop cool which is more the battle I'll have in the area I live in. The coragation in the metal should supply ventilation under roof but the bottom side of metal can get really hot.

 

[Coopnrun]

Keep in mind with the poly coragation roof, t hat a falling tree limb of any size is more likely going to puncture it. Had a small deck cover built out of it and many trees with rooting limbs falling.