Wednesday, December 21, 2016

Spray Foam and Rigid Insulation

The New House Next Door to the Pond got an insulation and air sealing inspection today. Next up will be a blower door test, to get some hard data on how well it was installed and if there are any holes that need filling prior to finishing the construction. In addition, an infrared camera can capture images showing where there is heat loss- and if we did that today, we would see a big hole around the cellar access door that needs to be addressed. (Other very notorious holes in building envelope are fireplace chimneys and skylights, neither of which were included in this project by design)

Spray foam in cavities, box beam; Rigid XPS at headers

In this super-tight building envelope design, all walls and roof surfaces have continuous rigid foam insulation, and the wood-framed walls and roof also have cavity insulation. The continuous insulation (CI) material is Extruded Polystyrene (XPS) and has an R-value of about 5 per inch. There is R-5 on wood walls, R-10 on basement walls, and R-20 on all roofs. The cavity insulation, for the most part, is open-cell spray foam with an R-value of about 3.6/in and is located between all exterior 2x4 wood walls studs and between 2x roof rafters and wood roof trusses. Closed cell spray foam was used in one location (the main floor box beam) and that has an R-value of about 6.5/in.

Recessed lights placed in soffits, not in building envelope

This design exceeds minimum R-value requirements of the "Prescriptive Path" of the Energy Conservation Construction Code, but air sealing is probably more important than R-value, really, so it's the high-tech barriers with taped seams and that CI that really make this system excel in the most economical way. Without CI, that infrared camera would show heat transfer at each wall stud and roof rafter; this is "thermal bridging"- the wood is a bridge connecting inside and outside. That won't be the case with the 1"-2" of CI on the walls and 4" CI on the roof.

If only cavity insulation is used, there would be thermal bridges/no insulation at each wall stud

I am very pleased about this project and the team that is working to create a house "built as all houses should be built", as the independent energy inspector stated today. (speaking from an Energy Code Compliance standpoint)
Raised-Heel Scissor truss allows for lots of insulation