Air Sealing from the outside
Looking for some input. We are starting a project soon in Cambridge, MA. The house is a large structure built in 1869. Air sealing the envelope is a part of the program. We are stripping the two (2) layers of existing siding to expose the sheathing. We are not removing the existing decorative trim (cornice, large corner boards, window trim, etc) so there is not an opportunity to add much rigid insulation. We are presently discussing the approach to air sealing the sheathing. The architect suggested fanfold insulation with tape. We are leaning more toward a spray on product such as EnviroDri though I am not sure as of yet if this product can be sprayed effectively on to what I assume will be 1x sheathing. Another alternative might be adding Zip wall sheathing system and leave it at that. I would like to do something more than wrap the structure in house wrap.
The walls section is (from the inside): lath and plaster, 2×4 balloon frame filled with cellulose (blown in some years ago), 1x sheathing board. I would like an effective air barrier with a high perm rate to allow the walls to dry seasonly. I am not sure yet how much we can add to the sheathing, but given that there are presently two layers of siding (clapboards covered with shingle) I would say there is at least 1-1/4” minimum. The new siding will be cement clapboard type siding.
Any input would from the gurus who frequent the site would be much appreciated. Thanks….
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