Ed Throckmortin
12/16/2012
Hi- I'm in contract for a 120' x 46' (pole) barn house in Sonoma and during the inspections questions have been raised regarding ventilation of the roof. The house/roof area is large and long with purlins running the length of the building. We do not think the purlins are drilled or offset. There appears to be some small vents on each gabled end and there is reportedly a ridge vent. Based upon the pest inspection, it seemed that the ~10" "attic" space is quite hot and there is moisture present, leading us to believe the venting is insufficient. A local roofing person came out, who was not an expert in barn or metal roofing, and stated that he did not know of a way to vent such a structure with the purlins effectively sectioning off very long sections of roof such that gable and a ridge vent may only vent the peak of the roof. There was also some talk that soffit venting may no longer be allowed due to fire codes. In short, we are due to waive our inspection contingencies on this property later this week and I would like to understand this potential roof issue prior to doing so. It seems like, perhaps, there is no issue. On the other hand, it sounds like this is a potential major issue down the road that I would like to have taken care of. Thanks much in advance
Todd Miller
Classic Products, Inc.
12/16/2012
This is the type of construction I have seen issues with before. What can you tell me about insulation and a vapor barrier. Is either present?
Guest User
12/18/2012
Thanks for your reply. I'm told it has "solar guard" a radiant barrier. I do see some fill insulation stuffed in spots where the ceiling trusses enter the roof. There is only about 10" of space between the drywalled ceiling and roof. The drywall tape has failed on the ceiling ridgeline that made me think about moisture. I'm told there is a ridge vent and I do see a channel vent on each eave (short side), but they are 120' apart.
Todd Miller
Classic Products, Inc.
12/18/2012
A great source of venting information is available at www.airevent.com To avoid condensation you need at least two (and preferably three) of the following: 1) A good amount of insulation 2) Good ventilation 3) A vapor barrier I am very concerned that you have a situation that could result in condensation.
Guest User
12/18/2012
I was able to track down the builder and the roof is constructed as follows: Galvalume +/- Solar-guard radient barrier (to be confirmed) on top of paper on top of sheathing with R-38 insulation between the purlins. There are continuous gable end vents on each end of the building, 120 feet apart (building is 42' wide). Thus, "there is venting down the length of the building along the purlins." Can gable end vents adequately vent this span and volume? Thanks.
Todd Miller
Classic Products, Inc.
12/18/2012
I am glad to hear that you have decking beneath the roofing. I did not understand that previously. That is not the ideal way to ventilate it. Adding a power exhaust fan to one end may help.
Guest User
12/18/2012
Well, it's Christmas and I am making my contingency clearing list, what should I ask for in addition to a power vent on a gable end? I gather that if I do have Solar-guard it's a vapor barrier. What if I don't? Any other thoughts? Also, can this installation have a whole house fan to keep the main house cool? Heck, might that help move air out those gable end vents? Thanks.
Todd Miller
Classic Products, Inc.
12/19/2012
The solar barrier may be a vapor barrier ... but it may not be one. Ideally the vapor barrier would be right behind the drywall though. Basically we want to prevent moisture from inside the living space from migrating into the attic where it will find cool surfaces on which to condense. I would not do anything which might introduce air from inside the home to the attic. I think the power fan in one gable can create enough air exchanges to clear out moisture and end the issues.

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