Guest User
7/1/2015
I recently purchased a pole barn structure to place my wood shop in and would like to add insulation to the building. The building is 42' X 72' and the bottom of the trusses (3":12" pitch) are at 13' (ceiling height) with the total wall height at 14'. The building is presently insulated with 1" foil faced Styrofoam sandwiched between the purlins and the exterior metal sheathing (the R value on the sheathing states R-7.2) at both the walls and roof. I have worked in wood frame construction for 38 years and thought I would apply the same principles of ventilation and condensation control to this structure as I had applied to homes in the past. I started yesterday by removing the foil faced Styrofoam between the eaves and the first roof purlin on two 8' sections to create a 1" air gap where the roof line meets the wall, to provide air flow from the eaves. I of course lost the metal roof support when I removed the Styrofoam so I supported the roof with 1" x 1-1/2" x 8" wood blocks (on top of the top wall purlin) alternating with 4" air gaps that I covered with screen to keep bird and insects out of the attic. This gave me exactly what I expected and desired, which was a 1" high x 4" wide air gap at 12" on center at the eaves line to provide air flow from the lower end of the roof. This morning when I went to start the next 8' section of the ventilation project, I noticed that the newly exposed metal roof panel (where I cut out the Styrofoam yesterday) was dripping wet with condensation. I'm sure if I did a good job of describing the situation that you probably already knew this, however I was surprised. I should mention that the remainder of the roof where the Styrofoam is in tact between the purlins and the metal roof the foil faced Styrofoam was not wet. I went to the internet to get information on ventilating with metal roofs and came across your site. I am hoping you can tell me where I may be going wrong since I know I don't want moisture and the resulting mold in my attic and walls. Here is a brief description of what I wish to accomplish. When I am finished with this project I would like to achieve these things. As much R-value as possible, a metal wall/ceiling liner on the interior (for reflective light and ease of cleaning) and to not have to deal with mold and moisture problems in the attic and walls. I would like your advise on how to proceed, so I will pass along what my entire plan was and you can advise me where I may be going wrong. This is a pole building so the posts, which are 8' on center will create a 7-1/4" deep wall cavity with 2" x 6" purlins, creating an overall wall depth of 8-3/4". I sourced out fiberglass blanket insulation 9" thick x 8' wide x 14'long to fill each wall cavity. The insulation comes with a vapor retarder on the interior side. The salesman for the insulation said that an additional visqueen vapor barrier would not be necessary. Also remember that the foil faced foam is between the purlins and exterior metal. My interior wall covering would be metal panels run horizontally over the posts. My intent for the ceiling would be to start by attaching a 4 or 6 mil. vapor barrier to the bottom side of the trusses and the same metal liner panels that I'm fastened over that, then blow in 12" of fiberglass insulation. This will create an attic space that I wish to ventilate by creating air flow from the wall/roof line as previously described, to a ridge vent or cupolas that I intend to install before insulating. Remember that I have the Styrofoam between the purlins and the metal roof as well. I only add that information in case it plays into any attic ventilation issues. I hope this gives you enough information to get us on the road to doing this job properly and I appreciate any advise you can give me. Thank you, Dale
Info @windowsonwashington.net
An informed customer is our best customer.
7/2/2015
Dale, I don't hear anything about exhaust (i.e. via ridge vent) here? If you haven't uncorked the top, nothing you do the bottom is going to help. Sounds to me like the foam was working? Why not just leave it intact and maybe add some additional insulation overtop?

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