# metal roof condensation



## johnnywalleye (Oct 12, 2009)

i own a camp that is 12x32 with a gable steel roof in upstate new york.the gable roof rafters are 2x6 with egg crate Styrofoam between the rafters and r19 pink faced insulation installed. the roof[top part of gable ,there is a ridge vent] . has condensation when we fire up the wood stove and there is snow on the roof.how am i suppose to stop this???should i install a plastic vapor barrrier over the craft faced insulation???please help, i attached 3 photos of what the roof and insulation looks like,and so long 4 now;john


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## johnnywalleye (Oct 12, 2009)

my bad roof rafters are 2x4


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## pyper (Jul 1, 2009)

The problem is that you're breathing.

Your breath is condensing on the cold metal surface.

Adding plastic would keep the moisture off the roof, but I wouldn't recommend it. 

Given the pictures, what you _should _do is put up drywall or some other approved finish surface. The insulation itself is no doubt marked that it must be covered, because it's a fire hazard. Hanging plastic would be an even greater hazard.

You mention that it's a (hunting?) camp building, so maybe it's not a big deal. I'd cover the insulation with something though, just to keep the fiberglass fibers from dropping into the brown pop.


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## johnnywalleye (Oct 12, 2009)

*i was hoping to*

not finish the cabin till spring,ill be snowmobiling out of there all winter long,if you believe its just water vapor from people breathing[there were 4 of us] what would happen if a crack a window for air circulation??


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## pyper (Jul 1, 2009)

You say there's already a ridge vent.

Opening a window won't hurt. If the condensation you're seeing doesn't "rain" down, then it won't hurt anything either.

Even if it does rain inside, there probably wouldn't be enough to do any real damage before spring.


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## johnnywalleye (Oct 12, 2009)

ok help me through this .you believe that come spring ,that i install ship lap pine boards on the roof trusses that should be enough of a barrier that will stop the rain from fallin in side the cabin???i dont want to go through the expense of the lumber to find out later that the wood didnt stop the condensation,it just made for an expensive umbrella


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## beaks (Jan 4, 2010)

I'm no expert but what I have read and been told leads me to think that you do need a vapour barrier. Along with that though you need a way to move the air and I'm not sure a passive ridge vent is enough. It looks like you have electricity in there; how about a bathroom-type fan, if it is a small enough space, or something similar upstairs to move the hot air outside?


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## Scuba_Dave (Jan 16, 2009)

Stuffing R19 insulation into a 2x4 rafter space gives you R13 effective insulation since you have now compressed the insulation - thus reducing its RValue
So sort of a waste of $$ to buy R19 for a 2x6 wall & push it into a 2x4 cavity

Warm moist air condenses against any cold surface
As the air heats up the moisture will condense against any cold surface
In this case the walls or ceiling that take longer to warm up
You can see the ridge vent from inside ?
You should not be able to see it :huh:

The paper on the insulation is Vapor _retarder_, you want the walls etc to breathe
Is their a moistuire barrier on the roo & outside walls - Tyvek/tar etc ?
Having an exterior barrier & an internal barrier (plastic) means any moisture that does find its way in between is trapped

Once the drywall is in place then the rafter space is sealed against more heat
Primer & a coat or two of paint does a pretty good seal
Plastic will not guarantee or stop moisture from condensing against a cold surface

Most likely you have moisture in the buiilding & new wood from construction
It will dry out
All IMO


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## johnnywalleye (Oct 12, 2009)

*condensation*

i really dont have much power there.a800w power inverter thats all.plus some 12vdc led lights,ill try to post some more pixs if you think it would help diagnose the issue.i will be puttin in no sheet rock.the ceiling will be shiplap pine 6in boards.will this be enough of a heat barrier to stop the heat from reaching the roof??i get the condensation only when there is snow on the roof and the cabin is very warm.


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## Gary in WA (Mar 11, 2009)

The tin has air channels already so you don't need the baffles. You need rigid foam boards, taped to stop air/moisture. You need a thermal break to the studs, to which the fasteners are holding the cold roof/walls: http://www.coloradoenergy.org/procorner/stuff/r-values.htm

You need to caulk/foam seal the joints carefully as a small leak will let moisture from the inside, through to condense on the metal. It has to be thick enough insulation to stop the heat from getting to the metal. For a vapor retarder: http://www.roofingcontractor.com/CD...icle/BNP_GUID_9-5-2006_A_10000000000000484938 The foam board should be touching the finish wood to not leave a gap that would be a convective loop for air movement. http://oikos.com/library/insulating_framed_walls/index.html


Easy as 1,2,3: http://docs.google.com/viewer?a=v&q...YOx1V4&sig=AHIEtbRO3lwafrsEmGYkoCq-P91xd-Qiaw

I’m still researching radiant barriers and bubble wraps, here is the general idea: http://www.ornl.gov/sci/roofs+walls/radiant/index.html


Be safe, Gary


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## johnnywalleye (Oct 12, 2009)

*thanxs*

for the info.it seems to me my easiest way out of this col drum is to install a radiant barrier.do you agree???


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## Gary in WA (Mar 11, 2009)

No, that won't be enough. I think foam is the way to stop condensation on the metal. The pine boards are loose fit (with gaps) all along their edges to let moisture through. You may need some plywood on top of the foam board that would act as a vapor retarder and a nailing surface for the pine boards that will move in size with the humidity changes.
http://www.apawood.org/pdfs/managed/J450.pdf?CFID=6331172&CFTOKEN=27731641

Using pine 1x6 boards, you have to realize they will shrink when the cabin is not in use and swell from 5/8-1” in 10’ when heated. http://www.woodfloorsonline.com/techtalk/woodwater1.html
It’s really a question of how far and how much do you want to spend?

Be safe, Gary


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## johnnywalleye (Oct 12, 2009)

*well then*

ill buy some blue Styrofoam sheets nail to the rafters and tape the joints,how thick of Styrofoam do you suggest??i can tell all ready this isnt goin to be fun.


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## Gary in WA (Mar 11, 2009)

http://www.buildings.com/ArticleDetails/tabid/3321/ArticleID/6061/Default.aspx

http://www.enersavesystems.com/pdf/Economic-Thickness-of-Thermal-Insulation.pdf

I'd cover it with a fire barrier especially with a wood stove and foam.....

Be safe, Gary


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## johnnywalleye (Oct 12, 2009)

*ok let me ask*

this????would i be better off then in buying the rools of bubble insulation that looks like foil??lowes carries the stuff and it seems to be heat resitance.its not cheap butits less time consuming than styro sheets and than an heat retarder.







thanxs for your help GARY and so long 4 now;john


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## Gary in WA (Mar 11, 2009)

That will only work for radiation, reflecting the heat from the stove back into the room. Or against the 1x4 strapping with air space next to the metal to reflect the sun warming the metal, defeating your warmth inside. Not convection or conduction: 

http://www.energyideas.org/documents/factsheets/PTR/HeatTransfer.pdf

More thoughts: http://forums.jlconline.com/forums/showthread.php?t=43900

Sunbelt States: http://www.fsec.ucf.edu/en/publications/html/FSEC-EN-15/index.htm

Be safe, Gary


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## johnnywalleye (Oct 12, 2009)

*now im more confused*

than ever????? according to the link you sent me my best bet is to add a 1inch spacer on every roof truss then nail 4x8 sheet of Styrofoam to that.which isnt a big deal.just more time and money.i still cant understand how the condensation is occuring.the per lings gave me 1 1/2 in of air space from the metal roof to the insuation.with the egg crates installed to make sure of that 1 1/2 air gap.is another air gap above the insulation going to make that much of difference????thanxs for all your help and so long 4 now;john


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