Air Sealing Roof Retrofit
We are in the beginning phase of repairing & renovating a 100 year old wood frame church in Somerville, MA.
We are considering our options to substantially improve the energy performance including upgrading the exterior envelope and overhauling and/or replacing mechanical systems. This will be a long process, maybe over 10 years. However, we need to replace the roofing immediately. We are going to remove the existing asphalt shingle roofing down to the sheathing and install new asphalt shingle roofing. The roofer has proposed Grace Tri-flex synthetic underlayment.
The majority of the roof is an unvented pitched roof cathedral ceiling (which makes sense it being a church!!) with a clear story on either side of the main axis. This roof is currently uninsulated. The roof structure is 1x plank sheathing on dimensional lumber (roughly 2x10). There has been some consideration of installing insulation (that would double as the air barrier) over the roof deck before new roofing but we are not ready to proceed with this and we need to replace roof NOW so defaulting to insulating the roof from the inside sometime over the next year or two. Anticipating that a closed cell spray foam that uses a blowing agent with a low GWP will be available by the middle of 2013... by which time we will likely be ready to remove old decaying plaster and wood lathe ceiling from interior, spray several inches of closed cell foam on underside of roof deck and fill cavities below with batt or cellulose.
Is there any point in exploring the potential to use the synthetic roof underlayment as an air barrier? If so how? tape? What about the permeance of the underlayment in this scenario? Does any of this make sense?
Posted Mon, 12/17/2012 - 12:01
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