So, if rafter is installed and you run stripping across rafters so metal will be exposed/open to the sight inside. Will you have moisture issues on inside of structure. There would be no paper or sheathing used just rafters cross stripping and metal installed.

Thanks

Yes, at least in my climate here in southeast PA. I've seen the inside of metal roofs in pole barns sweat to the point of dripping many times.

I say no, if it is not heated. I take it you are not heating a building with out something beside a metal roof.

X2.

You guys might be right given your northwestern US location. But here in the humid mid-Atlantic region I can guarantee you metal roofs condensate inside.

my 3 sided wood shed is exactly that tin over purlins

in WI weather it rains/drips in there several days a year , it is an air temp humidity thing

you really couldn't get more air movement 3 of the sides are actually fence panels and they stop a couple inches form the side on all but the back side

spring and fall humid air cold tin it condenses and drips all over , but it is a wood shed and it is dry 350 days a year so it does what it needs to for fire wood storage

In the right conditions it will definitely condensate and drip water inside . I know this from fact , my back shed is built exactly that way . M y shop is the same steel roofing with plywood and tar paper ,no problems .

I have built and sold countless cold storage sheds here in the upper Midwest and have never heard/seen an issue with condensation inside as long as cattle/livestock are not involved. That is the only times I’ve seen this and it is caused from their breath and body heat in cold weather. If you are really concerned though, many of the steel manufacturers here offer a fabric inside liner for ag buildings that comes from the factory applied to the underside. One of the names here is drip stop, and it does cost $. But as I said, even they only recommend in livestock applications. So there you go.

I haven't had that happen on the buildings I built for hay storage or the goats and pigs.

Great personal information, Thank You.
I suppose I could Tyvek then run tin just in case I would have an issue. Would that work as a back plan??

Roofing Felt, aka: Tar Paper is likely cheaper for what you want.

Yes. I didn't want the black look in there so I would think Tyek may work also.

Thank!

Poor ventilation would be the only way I'd see it could sweat being unheated

The roof over my deck creates condensation when the weather conditions are right but it isn't a problem.

If it is an enclosed building you are talking about I would go a long ways to try to avoid creating a "hot" roof.


Many places up here use 2x purlins over the rafters and screw the tin to those purlins. The goal is to create a roof that is strong but light. Adding plywood or osb just adds dead load to the roof. Once you have metal screwed to the pulins, it will be just as rigid as plywood would make it.

Also, in my experience, screws hold better in dimensional lumber than they do in plywood or osb

Put a vapor barrier on the Perlins then metal roofing, or you will be sorry, heated or not.

Some vou you guys just need to take us easterners word for it. It rains inside unheated buildings with exposed metal roofs under the right atmospheric conditions. it happens a lot.

Snowy, there's a product called Fan Fold, a foil-faced 1/4" thick expanded polystyrene, that some guys use between the perlins and steel panels to prevent condensation dripping inside the building.

My unheated pole barn sweats like crazy some days. I wish I had put Tyvek or something similar down prior to the tin.

I Think that is what I will do. It is possible some heat maybe installed someday in there on occasions. The barrier should help with that. Also if enough air flow and venting is available, when using heat should help with that problem.

Thanks 160.

Use Tryply (sp?) it is composed of two synthetic outer layers with a synthetic tar center. AKA engineered for the application, unlike tyvac or typar ......

If you have enough pitch,,,,plywood and composition shingle used to pencil out close to metal cost, if you are doing the labor yourself

They put a barrier up for pole barns here in ohio. Every time the weather changes there is moisture in my barn. Going from cold to hot. You would think it was only one time a year but every time it cold at night and hot in the day it can be a problem. The bubble wrap barrier helps keep the metal from dripping inside but all my tools and etc sweat too, not just the inside of the metal roof.

The barrier here is a big roll of foil bubble wrap. Silver foil on one side. Its like a bubble wrap house wrap. Venting the peak and eves really help though too.

https://rbwarehouse.com/bubble-insu...6TVCIrjtKz4oqW95Zw464lLTdAwaApQqEALw_wcB