Venting and finishing an attic of a timber frame home
I’m hoping some folks wiser than I can chime in with their thoughts on how to properly finish off the attic space of a former New England Barn.
In a nutshell here are the existing conditions:
-A 200+ year old Post and Beam building near the ocean. (good breezes)
-An unaccessible dirt floor crawl space with No vapor barrier
– Wall insulation : 1-2″ Encompassed Balsa wood insulation snaking between offsetting 2×3’s (airflow from the crawl space up thru the walls is good for air circulation and bad for R value.)
-2 finished floors of existing living space
-An unfinished attic space with fiberglass batt insulation covering the 2nd floor ceiling joists
-A new(ish) Architectural asphalt shingled roof
– wide wood planks as roof sheathing
– 4″x4″horizontal perlins spaced roughly 4′ apart vertically
– Ventilation is provided by windows in the attic which are opened in the spring and closed in the late fall.
My goal: To finish off the attic space as cost effectively as possible. My question pertains mainly to the ventilation issue for the roof assembly. I have read and spoke to a few people who say a cold roof system is the way to go. But in my situation the cost of furring and re-roofing a 50×40 roof is not palletable due to sheer cost.
My questions are: Would closed cell foam on the bottom of the roof assembly trap all the moisture coming up from the dirt floor crawlspace/living space? My thought is yes, and the potential stack effect would potentially compound the issue leading to a big risk of mold.
My alternative thoughts and I am hoping someone out there has experience with this:
I fur out the rafters and Insulate the roof deck with Rockwool. To ventilate I’ll cut in soffit vents down the eaves and use air baffles along the roof deck. At the perlins is my obvious problem- so my thought is to make some site built baffles (with some 1″ polyiso ridgid foam) to take the air from the air baffle on either side and tape off the connections with some HVAC tape. (yeah, that sounds crazy to me too!)
To vent to roof I was considering either cutting in a ridge vent about 6″ below the ridge or adding (2) 32″ x 32″ cupolas.
Just typing that makes me think I’ve lost my mind. So if you’re still reading and haven’t fallen off your chair laughing yet- my other thought is to not insulate the roof deck at all since this space is only going to be used in the summer months. I would keep the insulation in the 2nd floor joist bays. And perhaps utilize a whole house fan and a cupola to vent the hot air from the day out the cupola.
Is there a solution out there that I’m totally overlooking? I know I’ve lost my mind, but hopefully there is something that can be done to achieve the goal of creating useable living space for the summer months here in New England.
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