This is becoming a popular hybrid method of insulating. It involves building a frame wall 25 to 50 mm (1 to 2 in.) away from the foundation and then having a professional spray-foam contractor install about 50 mm (2 in.) of medium or high density polyurethane foam against the wall. The spray foam fills and bonds directly to the framing members and the wall, offering high insulation value (about RSI 0.98 [R-5.6/in.]) while reducing thermal bridging and providing a moisture barrier. The frame wall is then filled with insulation.

The primary limitation of this approach is higher cost, although its use reduces the need for additional materials and labour (see Figure 6-17).

Preparation

Discuss with the spray foam contactor on site what should be done before starting the spraying. Major issues such as active structural cracks and frequent and major water leaks must be addressed first.

Install the wood frame wall at a distance from the foundation as directed by the contractor, including both sides of the corner studs. Follow the framing techniques discussed in Frame wall with single or double layer of batt insulation.

Adding additional insulation

Once the contractor has installed the foam, the frame wall can be roughed in for wiring and plumbing and insulated. Again, a polyethylene vapour barrier is not recommended.

For details on treating the joist area, see Joist header space. For finishing, see the previous frame wall method in Frame wall with single or double layer of batt insulation.