Platt Builders 

Groton, Mass. 
plattbuilders.com

Square Footage after: Added 350 sf | Project Cost: $497,891

This project started because of a bad attic foam job done after the client had lived there for 20 years. The foam had been sprayed off-ratio and never fully cured. After two years of testing and planning it was decided that the foam and roof sheathing needed to go and that the rafters needed to be wire brushed, vacuumed, and. It was during this planning process that the client asked if the team could add a room or two in their newly-insulated attic. They designed a continuation of the existing staircase to flow up to the new third floor, added a dormer and windows.

Since the clients would not have any foam back inside the house’s envelope, the team had to devise a vapor and thermal system to protect the house decided on new Zip-roof sheathing, sealed with Henry Blueskin, a layer of 4” of external foam, 2×4 sleepers for venting and then another layer of 5/8” zip roof with asphalt shingles. They were certain this would create a virtual dew point so the client would have no interior moisture condensation. They insulated the cleaned rafters with Rockwool and then installed an Intello air barrier over that. Apart from massive disruption and risk of water coming into the finished house during the renovation, they needed to detail the exterior trim in such a way as to disguise the 6″additional roof thickness without making the house look like Frankenstein. They made the soffits deeper and beefed up the frieze band – the new look is elegant and integrated. 

When they designed the office, they were constrained to only have windows on one side due to the original geometry of the roof and the importance of not affecting the front façade. To compensate for the single run of windows, we made the office, sitting area and entryway carefully oversized.

Products:

Insulation: Intello air barrier, Rockwool
Sheathing: Zip-roof sheathing
Sealant: Henry Blueskin, external foam