What Is Green Building? A Home Builder Explains (Structural Insulated Panels)

In my last post, we spent some time looking at the pros and cons of traditional stick framing. In this post, we’ll be looking at popular alternatives to stick framing – SIP (structural insulated panels). As a reminder, the main focus of these blogs is the fiscal impact to the project; at what cost are some of these more popular energy saving systems available, and what will the utility savings be over time? SIP construction involves using panels that are filled with expanded polystyrene (EPS) for the exterior walls and roof. Typically, wall panels are constructed of 2×6 material, and roof panels are generally either 10” or 12” thick. The structure of the SIP is a wood member, with OSB (oriented strand board, often referred to as “chipboard”) plywood on either side, and EPS filling the voids between framing members. The panels are adjoined together with a “spline,” which is simply a wood framing member. There are several advantages to SIPs:

• Very low air infiltration rate; EPS is very dense and has virtually no air flow.
• High insulation value in the panels – EPS is an excellent insulator. When you combine a high R-value with a low air infiltration rate, you get a very effective insulating system.
• The panels are typically installed by a traditional framing crew, giving the Builder or Homeowner a relatively large labor pool to work from, resulting in a relatively low installed cost.
• Virtually no waste as it relates to the exterior framing of the structure. A typical stick framed home will have between one half and one large dumpster of scraps left over at the end of the framing stage.
• For the most part, the Builder/ Homeowner gets to skip the call to the insulation contractor; the wall and ceiling panels are already fully insulated.

There are a few downsides to SIPs as well:

• Thermal bridging (please see my previous post if that term is unfamiliar to you) is still an issue, as the structure of the panels is conventional framing materials.
• SIP panels are relatively quick to install, but the staging of them is quite time-consuming. Depending on the size of the home, anywhere between one and four semi trucks loaded down with panels will arrive at the job site, virtually all of which need to be unloaded by forklift and staged according to their place in the structure. Note – the panels will be loaded on the truck based on their size and shape to maximize trucking efficiency, NOT their order of installation, so it’s not at all uncommon to have perhaps 100 panels scattered around the property, with the installation crew spending a few days sorting them all out.
• Changes to window and door sizes are problematic and expensive.
• The electrical contractor will charge a premium for working with SIPs. The panels have “raceways” within the panels to accommodate electrical, but it’s time-consuming. Additionally, any field changes to the electrical plan in the ceiling, much like changes to windows and exterior doorways, are problematic and expensive.

So how do SIPs stack up against conventional stick framing? In my opinion, not terribly well:

• SIPs delivered to a job site, even when factoring in the insulation that’s integral to the panel, cost significantly more than a stick framed home.
• The cost of labor to install is generally about the same for either system.
• The total insulation performance of SIPs in some cases is only fractionally better, if at all. While I’ve not yet addressed insulation systems as part of this series, some of the insulation systems that over the past decade or so have become commonly available for a stick frame home are excellent and very cost effective.
• Added costs for the electrical contractor are significant.
• The limitations on changes to doors, windows, and electrical are a significant downside.

Next time, we’ll look at ICF (insulated concrete forms), which is a very different system of building altogether. Thanks for reading!