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Gatorboy
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Condensation with Metal Roofs
09/25/02 07:05 PM
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Help! I am still in the final planning stages of my Pole Barn, and have been reading on metal roofs, and the condensation thing has really gotten me worried. I had planned to put a metal roof right on the purlins -- but to avoid the inside "rain", I think I should put up plywood first. Does anyone know if trusses 8' O.C. with 2x4 purlins on edge 24" O.C. have enough strength to handle plywood being installed on it? If so, I have started to think, gee, if I've got the plywood up, why not just put up shingles.
Cowboydoc over on TBN had talked about insulating a metal roof. Does that mean putting some corning fiberglass between the purlins? I am confused -- pictures on how this is done would be very helpful, if anyone has the answers for me.
My Pole Barn plan is getting so many daily revisions, I don't know when I'll be finalized so I can start setting my posts. 
:: D A V E
:: g a t o r b o y
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AndyF
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/25/02 08:40 PM
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Your materials supplier should be able to get you the ceiling insulation you'll need for the pole barn. The insulation is either 24" or 48" wide depending upon your truss spacing and has a vinyl face which faces inside. If you have an 84 Lumber store near you, take a look at their ceiling as this is what they usually use.
Your truss spacing is really too large to deck with plywood. If you really want a plywood deck build the roof like a house roof with the trusses on 24" centers and no purlins. Check with your neighbors to determine if condensation is really an issue in your area.
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SteveB
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/26/02 07:42 AM
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Generally with a metal roof you would use a type of faced insulation that goes over the purlins and under the metal sheets. I used 4X8 1/2" R-4 rigid sheets sheets (TUFF-R) for my roof insulation. Performance is excellent but screwing down the roof was interesting because the sheets had a tendency to compress. I would not recommend this method for that reason. I brought up this issue on TBN (there is a hole thread on it there) and CowboyDoc said there is special insulation for this purpose. It is plastic faces and comes in a roll. You just roll it out under the sheet you're puting down, staple it tight (I'm guessing), and slap your metal panel down on top of it. He said it compresses down to nothing between the purlin and metal sheet. This avoids the problem that I had.
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cowboydoc
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Re: Condensation with Metal Roofs
[re: SteveB]
09/26/02 08:31 AM
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Steve and Andy are right. It's too far apart for plywood. You need 24" on centers for plywood. The roll out insulation is very easy to do. It's also very easy to put your metal tin right on top. If you can't find it I will get the exact name of it for you.
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Gatorboy
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Re: Condensation with Metal Roofs
[re: cowboydoc]
09/26/02 08:55 AM
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Does this insulation get rolled out on top of the purlins?
Here is a picture on TBN of the felt paper in your barn.
I don't see any insulation up there. If you don't have it, then where would this insulation be placed -- between the metal roofing and the purlins?
:: D A V E
:: g a t o r b o y
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fenneran
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/26/02 11:17 AM
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Last year I finished the second floor of our Cape-Cod style house. It was built around 1925 and has a metal roof. The metal was right on the purlins. We found some thin foam panels at Lowe's made for this purpose. They are about 2 1/2 - 3 feet across and in the general shape of a flat "W"
Kind of like:
__
We stapled these under the purlins, then stapled the regular bat insulation under that. This way, if there is any condensation, it is channeled away from the insulation and down to the bottom of the roof-line. Although I have never seen so much as a drop come down, it may have during the middle of the winter.
Don't know if this applciation would help in the barn project, but thought I would share.
Frank
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egon
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/26/02 06:27 PM
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Dave:
The 2x4 purlins are probably too small to span 8 ft. It may be advisable to have the roof design checked and ensure it confirms to your areas codes.
Longer purlin spans require larger purlins which in turn requires a truss that will support more load. The sizing of one is dependent on the other.
The truss suppliers have all the information.
Egon
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Phred
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Gatorboy,
As mentioned above you need the roll insulation. I think it has an R value of about 13. In the attached picture you can see the white vapour barrier on the walls and celling that is the inside lining of his type of insulation. This is standard for metal buildings which all use the metal roofs. These buildings also use it for the walls. The bag in the right hand part of the photo contains a bunch of scrap pieces. Its basically a few inches of fiber glass with a platic vapour barrier.
Fred
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Phred
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Here is a shot of the raw material, pilled up out front, prior to the roof going up.
Fred
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cowboydoc
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/26/02 08:31 PM
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Gatorboy,
I've got several barns and that one doesn't have it. That's one way I know you want insulation because that one drips all over everything, esp. with animals in it. I will get you some pics tomorrow of what it looks like in the the other barns.
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farmhouse
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/26/02 09:38 PM
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I'm just having a 50X34X20(hgt) pole barn built. Should be finished next week. All metal and fully insulated. I watched the process of insulating. The insulation came in rolls with a plastic side which was placed down on the purlins. The unfinished side was placed toward the metal. They did not promise that it would deliver R factors sufficient to keep us toasty warm but was primarily to offset the traditional coldness of the metal building. I think the company, Apache Construction is great but unfortunately they are regional to East and Southeast Texas. By the way, they used purlins on 3 ft. centers on edge (2X6) and did not use decking. Engineered scissor-type trusses on 10 ft. centers.
Romans 8:28
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Gatorboy
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Re: Condensation with Metal Roofs
[re: cowboydoc]
09/27/02 05:08 AM
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Everyone,
Thank you for the excellent information. I am coming out of the haze, and it is now getting clear to me.
I will get some of this rolled insulation and put it over my purlins before laying on the metal roof.
Not sure about everyone else, but sometimes I have a hard time visualizing something that is just in writing -- like they say, a picture is worth a thousand words. 
:: D A V E
:: g a t o r b o y
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Bayrat
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/27/02 06:40 AM
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I wonder if that spray on insulation would do the trick for the ceiling? I had an estimate done for my shop walls and it is just too expensive for my taste, but for the open ceiling, it might be a good idea  .
Bayrat
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cowboydoc
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Re: Condensation with Metal Roofs
[re: Bayrat]
09/27/02 08:25 AM
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The spray on is extremely expensive. $1.25-$1.50 per square foot of sprayed space. Compare that to about .10 a square foot to do roll out insulation. About the only time I've seen this used is when insulation was needed later on. I had thought about doing it in that barn that gatorboy posted the pic of but for a 45x65 barn it was going to be over $4000. I only spent $8k to build it!!!
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Bayrat
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Re: Condensation with Metal Roofs
[re: cowboydoc]
09/27/02 02:28 PM
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I agree, that is why I did not use it for my shop area. I am going to use fiberglass for the walls, the ceiling is already done. If I ever decided to insulate the storage area, I would go with the spray-on for the inner side of the steel roofing. Is the material that is being suggested here insulation or is it more of a vapor barrier?
Bayrat
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cowboydoc
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Re: Condensation with Metal Roofs
[re: Bayrat]
09/27/02 02:38 PM
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It's used for both bayrat.
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chevdog
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/27/02 08:47 PM
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Providing adequate ventilation is a big part of controlling moisture. That's why they install soffit and ridge vents (or air turbines/exhaust fans) in the attic of your home. You can buy prefab ridge vents in 10' lengths with a 9" throat opening that will help to reduce the temperature differential at the roofpanels. I would still add the insulation, but with some additional ventilation you should be dry and happy.
Nick
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Argee
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/27/02 09:34 PM
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Here in the somewhat cooler regions of the country they use dow board on the trusses before the metal goes on. But I'm not sure it would work on 8' OC, which of course is unheard of in this part of the country.
Argee 
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MelonHead
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Re: Condensation with Metal Roofs
[re: Gatorboy]
09/30/03 04:28 PM
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Hi Dave-
I'm at the same point that you are RE planning for a new workshop. I want it insulated and I'd also like to have the inside walls covered with OSB or plywood instead of the fragile plastic covered insulation which I'd tear up.
I'm thinking of going with Structural Insulated Panels such as these
They can be placed on rafters 8' OC.
The nice thing is are girts/purlins, insulation and inside decking (OSB) all in one! And the insulation qualities are excellent.
I'm still looking at this. Anybody have any experience with SIPs?
Thanks.
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GaryM
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Re: Condensation with Metal Roofs
[re: MelonHead]
10/01/03 07:53 AM
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The exterior walls on my new house, not yet completed, are SIPS by Enercept http://www.enercept.com/
They were delivered precut per the plan and went up pretty quick. There were some issues with the wall panels because the GC didn't rip the PT sills to ensure that they were 5 1/2 inches wide.
My roof is not SIP, just the walls.
Gary
----------------------------------------------
Hey! Aren't you supposed to be working?
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Re: Condensation with Metal Roofs
[re: Gatorboy]
10/09/03 12:37 AM
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I built a 40x60x14 this summer with help from family and friend and your supplier will have the insulation you need. It is only about 1" thick in 4' rolls, tack it to the purlins plastic side down just before you apply your roof siding, the weight in minimal, your condensation problem is solved, and and it is alot quieter when it rains. I went with a kit, and stepped up to the upgraded kit which got me the insulated roof 1' eaves on all 4 sides and soffits for $900 more. So based on that I'd say that insulation is pretty cheap. My 2x6 trusses are 4' on center, the purlins are layed flat 2' on center. Now my farmer buddy down the road has a 40'x48x16 , pole barn/ garage with 2x6 trusses 8' on center with the purlins on edge (like your talking about) with the same type of insulation under the metal roof. He has had no problems at all, in SE Michigan, In fact he told me everytime he helped me build that I wasted my money going 4' on center with the trusses but, my kit barn went up really well. One thing I would recommend since you are in the planning stage is to raise that barn site alot. I know so many people (horses) with wet barns because they built and then then tried to fill or solve their water drainage problems. So the first thing I did was bring in enough fill to raise my barn site 2', good luck with your barn 
Edited by hockeyhead (10/09/03 12:53 AM)
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