Spray Foam Exterior Insulation with Stand-Off Furring - New York

IBACOS and Green Homes America 1 (GHA) collaborated with the New York State Energy Research and Development Authority (NYSERDA) Advanced Buildings Program to research a variation of a commercial curtain wall assembly for residential construction as part of a comprehensive whole-house deep energy retrofit (DER) package. The advantages of this strategy include minimizing the physical connections to each individual existing wall stud, using closedcell spray foam to encapsulate existing siding materials including lead paint, and creating a vented rain screen assembly to promote drying. As Moore (2011) states, "Closed-cell foam acts as air-sealing, insulation, and secondary drainage plane..." Field installations on a limited number of houses indicate that the incremental cost when installed as part of a typical siding and window replacement job adds approximately $10/ft2 of wall area.

2 x 4 framing members were attached to the wall at band joists and top plates using "L" clips, and spray foam was used to insulate the wall after the framing was installed. Windows were installed as the framing was put up, including extension jambs.

Key lessons learned include the following:
(1) The installed cost of the spray foam system was comparable to the installed cost of the rigid foam and furring strips.
(2) Spray foam should be applied in such a way that it locks the framing members in place before the remaining foam is installed in the field of the wall. The spray foam has a tendency to move the new wall framing as it expands. Best practice is to "picture frame" the wall framing with spray foam and then apply the spray foam in the field of each bay.
(3) Variations in the existing siding conditions must be accounted for when attaching the ledger boards and wall framing. A best practice is to uniformly shim the ledger boards off the walls so the new framing is a uniform distance from the ledger boards and the inside surface of the interior framing. This is important primarily for window and door installation and the associated extension jambs and trim.
(4) From a sequencing perspective, it is advantageous to replace the windows at the same time as the exterior walls are being built. This requires a crew that can perform a number of different tasks (e.g., framing, flashing, window install, trim carpentry) and does not lend itself to subcontracting this approach piecemeal (e.g., framing subcontractor, window installer, drainage plane installer, trim carpenter).
(5) Application of the brackets and associated fastener screws was more time consuming than anticipated.
(6) It is important for the spray foam contractor to perform all preparatory work, which in this case included placing plastic over the windows and exposed foundation to minimize or eliminate the possibility of damage due to overspray.