Hope and dreams

[one more]

Hi all, I'm hoping to build a shack this summer and was wondering about metal roofing. Will it be raining inside? I plan to have a copula, so I know that will take care of most of the steam but should I sheath the roof then put the metal roof on or can I skip the sheathing? Budget is a factor, so I'm trying to figure out where I can trim it. Thanks for your thoughts.

[Cedar Eater]

Yes, it will be raining unless you prevent it. Sheathing the roof and then putting metal on it is not a good approach because the metal needs breathing space beneath it. Last year there was a thread here where a guy detailed a design that provided proper ventilation under the metal and a vapor barrier and wood ceiling. I can't remember his name or the thread title, but it was March and April of 2015.

[Super Sapper]

There is an insulation that pole builders use in cattle sheds that was reasonably priced when I did my addition to the garage. It has plastic on the underside and does not drip.

[lpakiz]

Wood sheathing on the rafters, felt paper on that and then steel. In my 5th season and havnt had a drip yet.

[pipewhiner]

I used 1"x24" foam board between my purlins and then the metal roof over that. It worked great.

[CampHamp]

My neighbor went without sheathing and it rained. Then he added a steam hood and it stopped and he boiled faster. Maybe put your sheathing money in a hood?

[Cedar Eater]

I've seen some pics here lately of steam hoods made of plastic sheeting that look pretty inexpensive. I would be very wary of putting painted steel directly on a flat surface. The manufactures recommend against it. All that I've seen specify ventilation under the metal to protect the paint from overheating when the sun shines on it and to allow the underside to dry sometimes.

[one more]

I figured it would rain! I was thinking of sheathing and then purlins on that to connect metal to but giving it breathing room as well?? Fabricating some sort of hood may be the way to go as far as cost savings! I appreciate all the input, so many things to consider it makes my head spin. Lol.

Matt

[Cedar Eater]

I figured it would rain! I was thinking of sheathing and then purlins on that to connect metal to but giving it breathing room as well??

The amount of ventilation that passes through the ribs of the metal probably isn't enough, so you would have dead air spaces between the purlins. If you put the sheathing on the underside of the rafters or stand the purlins off from the sheathing so that air can pass under them from soffet to peak, the heat buildup under the metal is much less.

[CTsap]

14042
If you decide to do sheathing, you can put a breathable membrane down and then strapping ontop. The strapping will give you something to screw the metal roof into. Also gives you something to stand on while installing.

[CTsap]

14041
If you decide to do sheathing, you can put a breathable membrane down and then strapping ontop. The strapping will give you something to screw the metal roof into. Also gives you something to stand on while installing.

[sap retreiver]

I put 1" pine boards down, tyvek, strapping vertically then another layer horizontally. On occasion I get a little bit of condensation but not very often

[TedA]

Not sure what "breathing" space a metal roof on an outbuilding needs. I'm in agreement with Ipakix. Put down wood sheathing (5/8 is good) on the rafters, cover it with felt and attached the metal roofing. Mine has been up a year and doesn't seem to "overheat". Cupolas are less efficient in removing steam (in my opinion) than steam hoods so when we moved our operation inside, I went with a steam hood. Very little, if any, steam makes it outside the hood so there is no significant moisture going up into the rafters. Some pictures are attached.1427614277

[Cedar Eater]

Not sure what "breathing" space a metal roof on an outbuilding needs. I'm in agreement with Ipakix. Put down wood sheathing (5/8 is good) on the rafters, cover it with felt and attached the metal roofing. Mine has been up a year and doesn't seem to "overheat". Cupolas are less efficient in removing steam (in my opinion) than steam hoods so when we moved our operation inside, I went with a steam hood. Very little, if any, steam makes it outside the hood so there is no significant moisture going up into the rafters. Some pictures are attached.1427614277

What did the manufacturer of the roofing recommend?

[maple flats]

I have steel roofing directly on purlins spaced 8" apart and the purlins are directly on the trusses. The first year it rained. Ever since then I've had a hood and I get no rain. My roof looks like new underneath but has faded very slightly on top. Looking at it the fading is not apparent, but when I look at pictures from the early years I can see it. My roof was put on the first weekend in Jan 2004.