Project manager Mark Pollard points out where his crew has placed a Grace membrane capillary break between the old home’s existing block foundation and its existing sill beam in this photo from December, before severe weather struck New England. The crew is now tying this membrane into an air barrier membrane for the home’s walls as part of detailing the building’s new airtight and insulated exterior weather barrier.
Pollard explains the exterior air barrier and insulation assembly on a freezing cold day in February after a succession of blizzard snowstorms. Visible here are OSB bucks used to extend the window openings; Grace polyethylene and bitumen membrane applied as an air and vapor barrier to the existing board wall sheathing, and integrated into the Grace membrane inserted earlier as a capillary break at the joint between the foundation and the floor frame; a 1.5-inch layer of foil-faced polyiso insulation appied over the air barrier membrane, attached with cap nails (joints sealed with Dow Weathermate tape); and a top layer of 1.5-inch foil-faced polyiso attached with four-inch screws and washers (joints sealed with 3M 8067 flashing tape). Not yet installed here are beveled clapboards in the window sill openings to create sloped drainage, which will be topped with more membrane integrated into the drainage plane formed by the foil-faced foam. “We’re not doing that yet because we don’t want it to get beat up before we put the windows in,” said Pollard.
Another cutaway view of the air barrier, insulation, and window buck detail. 3M 8067 tape has been used to seal the building corner joint in the air barrier membrane, and to seal the air barrier to the window bucks. “The window bucks are part of the air barrier,” explains Pollard. Around the corner on the wall at left, window bucks have just been set and the foam installation has not yet started in this photo.
Using a 3-inch rip of 2x4 as a depth gauge, carpenter Ed Muennich nails an OSB extension window buck into the existing wall framing.
Muennich uses a 6-foot level to check the alignment of three side-by-side window bucks as the crew builds out the wall.
Carpenter Shane Fenton applies 3M 8067 flashing tape to the Grace membrane on a wall and wraps the tape around the corner to complete the seal. The 3M tape stays flexible and sticky at surprisingly cold temperatures, but the crew needs to work without gloves when applying tape, in spite of the bitter cold weather.
Creating the airtight barrier under the insulation on the house wall requires meticulous hand labor and attention to detail.
Shane Fenton rolls the 3M tape with a hand roller to help establish good adhesion. The tape grips tenaciously even in cold weather.
Carpenter Chris Mitchell cuts a notch in a sheet of foil-faced polyiso foam in order to fit the foam neatly around a roof rafter tail. Thompson Johnson has opted to fit the insulation and air seal around the existing rafter tails for this job, rather than cut the tails off and run the air barrier continuously up the walls onto the roof.
Mitchell trims the edge of the insulation sheet with a knife. Corners and eaves create challenging and laborious detail work on this project.