Amber Wood, PE

Deck the Walls with Insulation

Where do I start?! This is one of the most common questions for those aiming for a highly energy-efficient new or remodeled home. Builders and remodelers, especially those new to high-performance building techniques and practices, often want to know what the low-hanging fruit is as they start their journey toward energy efficiency. Usually, my first response to these questions involves air sealing and insulation. In order to improve comfort and reduce utility bills for a home, after all, the goal is to create an efficient building envelope, add ventilation for fresh air, and then right size the heating/cooling equipment for that space. To make this post more "fun-size" (like all the Halloween candy in the stores this time of year) I'll focus just on one part of this recipe for energy efficiency — best practices for insulating walls.

To provide a more detailed backdrop to my comments, I want to point you to an article Home Innovation Labs authored in Professional Builder magazine titled, “11 Tips for Mastering Building Envelope Design.” The article includes information on best practices for creating tight, efficient building envelope systems. The next step is to ensure that there is plenty of fresh air using ventilation. Then we come to the star of this show ... wall insulation.

There are a variety of wall insulation types and each has a different insulating value. Generally, these include:

• Structural wall materials with insulation: Structural Insulating Panels (SIPs), Insulated Concrete Forms (ICFs), etc.
• Rigid foam: EPS, XPS, polyisocyanurate, etc.
• Batt insulation: fiberglass, mineral wool, plastic/natural fibers, etc.
• Blown insulation: fiberglass, cellulose, mineral wool, etc.
• Spray foam: open or closed cell

One Step at a Time

There are basically three considerations for insulating house walls an selecting the right type of material for your particular project.

1. Structural Support and Wall Framing Type: Optimizing wall insulation begins with looking at the framing type. For wood-framed construction, you want to allow as much area for insulation as possible. A typical wood-framed house has about 25% of the wall surface area that is wood. The more efficient the framing is, the more room there is for insulation. However, the cardinal rule is that the house has to stand structurally first, and then allow for as much insulation as possible. One way to systematically reduce framing is through panelizing walls. Beyond wood framing, there are other structural materials that integrate the support of walls with insulation such as SIPs or ICFs.
2. Exterior Insulation: Once the structural support and wall framing type is decided, consider adding exterior insulation. This is a great way to insulate because it eliminates thermal bridging through the studs and increases the whole-wall R-value.
3. Insulation on the Interior or in the Wall Cavities: Finally, consider the interior insulation or insulation in wall cavities. There are a variety of ways to insulate in wall cavities with a range of R-values including combinations of insulation materials such as flash and batt (i.e., a small amount of spray foam “flash” used primarily for air sealing that has a bit of R-value with batt insulation used for the majority of R-value). Often, the wall insulation decision comes down to cost. Something worth considering, however, is the combined cost of the material and labor. While it is possible to get a high performing wall system from any of the insulations listed above, some have higher initial costs and others require more labor for the same installation and resulting performance.

Ultimately, the goal is to outperform the design ... and your competition. So how do you ensure that your design is optimal for your climate? The Home Innovation Research Labs is currently studying high-performance walls to address the integration of structural, thermal, and moisture performance. Stay tuned to this blog for those results in the coming months.

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