I read many pole barn insulation articles and questions threads before asking this…
DuneWoods
| Posted in Energy Efficiency and Durability on
Hello, I’m planning to remodel a 30’x32′ post frame barn in zone 4A and will be adding solar panels to the roof on one side. The barn will be my weekend wood shop for now, so not always heated and cooled, but I’m hoping the initial insulation effort will reduce how much energy is needed to heat/cool when needed. Initially, I’ll have a window A/C and wood stove. When I retire, maybe it will be occupied more and HVAC will be added. I’ll probably target around R38-45 for roof and R19 on walls. I will be removing all metal and replacing some water damaged girts and doors/windows. I think I’ll add sheathing/tape/wrb to the roof and walls but am in a state of decision paralysis regarding the insulation approach as I get to the roof.
The barn has a full foundation, not just piers for the posts. The dirt floor will be dug out and insulation and vapor barrier applied before pouring a slab inside. The roof is 2×10 rafters, 24″ OC, that just run straight up to a central ridge beam, so no trusses but cathedral style with a second floor loft space. Rafters end flush with the exterior wall girts, so the only way I’d know to add roof ventilation is to add tails to the rafters so vented soffits could be added. There is conduit running up near the purlins, so getting an unobstructed roof vent pathway may require moving conduit.
I’m leaning toward an unvented roof with above sheathing insulation. I’ve found someone selling reclaimed 3″ xps from a commercial roof replacement that could be used under slab and above sheathing. I’d go with fiberglass batts on the interior, which would put me at a potential R40-45 roof if I assume reclaimed XPS may not have the full R15 potential.
Would I have issues if I totally sealed this building and did not maintain climate control full time? Would I need to keep a dehumidifier in there for the times it’s sitting unconditioned? Or would it be better to consider putting in the extra effort to get a ventilation channel below the sheathing and add the soffit and ridge vents? Or maybe a shuttered gable vent/fan setup? Every pole barn contractor I’ve spoken to around here just says to spray foam it and be done..
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Replies
DuneWoods,
I think your plan and the roof you propose will work fine. Typically the reason houses in climate zones above 3 have moisture issues are that a) occupants and their activities generate it, and b) the building is heated above the outdoor temperature so it can hold more moisture - moisture that can condense as it moves through walls or roofs towards the cooler outside surfaces.
When left unconditioned, your shop shouldn't experience those conditions. Most insulated unconditioned outbuildings do just fine. Some do get a bit damp at times and benefit from ventilating the interior, or infrequently may require dehumidification, but I'd be very surprised if that dampness affected the walls or roof itself.