Recommended plywood thickness with a metal roof?

[Rachela]

See my earlier post...



My biggest concern are the 2-3ft, crazy wet and heavy, March snow storms that we sometimes get. Therefore I built the rafters very solid (probably overkill) with hurricane ties and proper 16" spacing. Nothing is bringing that roof down!

I also used a cathedral style roofing techniques, using a ridge beam versus a ridge board, providing even more stability and putting ~75% of the weight dispersal into the beam and walls instead of the rafters.

So in the end, with only 25% of the weight being on the rafters, add to that I did the 16" spacing and have a ton of rafters solidly built and hung properly (right amount of nails, using the right ties, etc.), I could use thin sheathing because it only serves a couple of purposes:

1) moisture barrier
2) helps distribute weight across the rafters more evenly
3) provided a nice surface to attach the purlins

I used rafters, sheathing, purlins, felt, then metal. Primarily because when condensation occurs, and it will, I do not have to worry even a little bit about it. Not only is there air circulating under the metal (because of the purlins) to assist in drying but any drips are then caught by the felt. If by chance (because I reuse a lot of materials so things have holes in them) it drips, then the plywood catches that.

Nothing gets in from above!!

I detail this all out with pictures in my trailer thread, might take a bit of digging to find which page has the right pics but they are there. It's very easy, I have no carpentry skills and had never built anything before.

Good luck

Very detailed thank you for this help

 

[imnukensc]

Didn't use any plywood. Not necessary, IMO.

 

[ColoradoPip]

Didn't use any plywood. Not necessary, IMO.
View attachment 2112369

Easier to get away without this if it's (a) an outdoor run and/or (b) in a warm climate.

If you are using metal roof for the coop itself, and have cool (or cold) nights, then the exhaled air and warm poop from the chickens could cause condensation which could drip inside the coop. With a sloped roof, it should drip far away, but these are all just things to take into consideration.

I'm not 100% convinced there is a "right way" to installing the metal roof. The only consensus seemed to be...use purlins (like you have done also), and even that was still contested as not necessary, especially if you use plywood.

 

[Rachela]

Easier to get away without this if it's (a) an outdoor run and/or (b) in a warm climate.

If you are using metal roof for the coop itself, and have cool (or cold) nights, then the exhaled air from the chickens could cause condensation which could drip inside the coop. With a sloped roof, it should drip far away, but these are all just things to take into consideration.

I'm not 100% convinced there is a "right way" to installing the metal roof. The only consensus seemed to be...use purlins (like you have done also), and even that was still contested as not necessary, especially if you use plywood.

I’ve heard about just putting right on top of felt and plywood without the purlins.

 

[ColoradoPip]

I’ve heard about just putting right on top of felt and plywood without the purlins.

Yup. When I researched metal roofs, I saw pictures of every imaginable setup. Funny thing was each piece of the setup had people using it or not, and telling you why is was or was not necessary. Some said you don't need felt, some said no purlins, others no plywood, it seemed like the only thing people agreed on was metal and rafters, lol. Others said, do it all or you'll regret it later.

Eventually I decided that opinions are like TP, everyone has..oh wait...ok opinions are like opinions, we all have some , and just evaluated my variables and built it to what I thought would work the best for me. One thing for sure by using all of the recommended materials...I do not need to worry about it leaking or building condensation.

The morning after I put the roof on, it had condensation rolling off the outside of the roof because of the cold nights and intense sun here. Even after 6-8" of wet heavy snow melted, not a drip inside.

All I would recommend is evaluating the variables to make the best decision for yourself

 

[aart]

I would for sure go for some kind of sheathing under the metal.
Probably doesn't matter much how thick depending on your framing.
Got pics of your coop @Rachela

 

[easterbun]

Admittedly I live in the south, but our house roof is metal and it's just on top of purlins... there's no underlayment at all.

 

[Rachela]

I would for sure go for some kind of sheathing under the metal.
Probably doesn't matter much how thick depending on your framing.
Got pics of your coop @Rachela

Getting there slowly, we have had rain.

 

[aart]

Getting there slowly, we have had rain.

Can't see the roof!

 

[Rachela]

Getting there slowly, we have had rain.

Only 2 trusses up and it started to rain