Jeff Eby
2/16/2016
I had a small apt added onto my existing pole building for my son last year it has engineered roof rafters of 2x3 top and bottom with osb I shaped rafter. this they sheeted with 7/16 osb then a synthetic underlayment and then they screwed the 3' wide painted metal roof on top of that. I then put bat insulation in between the rafters and not heated it while I have been wireing and plumbing the building this winter. I have purchased and poly finished the toung and groove notty pine to go up next. I have ice from condensation on the underside of the osb above the bat insulation so I have stopped and not gone any further till I can fix this problem. the roof has a ridge cap and no overhangs with metal on the wall same as the roof. I am in the process of removing the bat insulation now so I can thaw and dry out the osb before it starts rotting. this is a story and 1/2 building with a loft bedroom and will be cathedral ceilings. please help as the contractor is now out of business and the three others I have consulted with locally don't have any experience with this type construction and I want to fix it right.
Eric Novotny
An informed customer is the Best Customer!
2/16/2016
Nothing about the insulation is stopping the moisture migration and by putting up the insulation, you have thermally uncoupled the OSB from the room side heat. As that OSB gets much colder, dew point is reached. The room side needs a proper air tight barrier and some vapor control as well. This will limit the moisture transmission to the backside of the OSB and the condensation. T&G ceiling is not at all airtight and your vapor barrier detailing needs to be spot on in this case.
Guest User
2/17/2016
Yes I understand this principle now after much research but what I am looking for is some suggestions on the best way to fix the problem. I have been told by a local contractor to remove the steel and put 1x6 strips down and replace metal. another has said to do the same but put down 1" foam then strips under the metal and have the underside of the osb spray foamed. on another web page I read that I need to put plastic sheeting between the t & g and the insulation and tape all the seems. but this doesn't sound like a long term repair as I know that tape always deteriorates and the seams will not be air tight in a few year when the glue on the tape deteriorates. what I was thinking after all my research is to put 1 x 2 blocks in between the rafters and a 1" foam board to create a 1" air space with a ridge vent and eve vent. then plastic sheeting in a single sheet as building is only a 24x36. then putting the 1x6 stripping under the outside steel. but this is only my thoughts and I am not sure if this is the best way or totally wrong. or if their is a better, easier, or more cost efficient way or what?
Eric Novotny
An informed customer is the Best Customer!
2/17/2016
No need to tear off the roof. Is the plywood vented? i.e. is there venting between the top of if the insulation and the roof deck or is that solid?
Guest User
2/17/2016
no it is solid
Eric Novotny
An informed customer is the Best Customer!
2/18/2016
If the plywood is sealed, I would just treat it as a non-vented space. Spray foam will be the easiest here.
Guest User
2/18/2016
how much spray foam for instance just a sealing layer or several inches? and would I then need to run a dehumitifyer as I am using boiler driven baseboard heat in this building.
Eric Novotny
An informed customer is the Best Customer!
2/18/2016
Jeff, I would contact an installer and see what they recommend. Closed cell is preferred in roofs for the vapor diffusion control in this case. Eric

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