Sunday, March 20, 2011

Building costs, stick framing vs. panel construction?

The most common form of residential construction in the US is stick framing. This is a tried and true technology that has been in use for over 100 years. It is so widely used because it is fairly efficient from the stand point of material usage, material cost and construction speed.

But, stick framing is not perfect. It may be an efficient way to build walls, but it suffers from a couple of deficiencies. Because a wall is constructed of many, many parts, it can have excessive air infiltration reducing energy efficiency. Another issue is thermal bridging. Because the studs span from the interior surface of the wall to the exterior surface, thermal energy is transmitted with less resistance through the studs than through adjacent insulation reducing energy efficiency. And lastly, because a standard wall is made from 2x4 dimensional lumber, there is simply not space to add enough insulation to attain high enough thermal resistance. All these factors added together produce a wall that is not particularly energy efficient.

In order to try and improve the energy efficiency of stick framed structures, we are now going to extreme measures. These include increasing the thickness of walls to 6”, 8” or more. Another option is to build two walls adjacent to one another with space between, increasing the space for insulation. We also add various types of foam sheathing to the exterior surface to increase the insulation value of the wall and reduce thermal bridging. Some people also add wood strapping to the interior surface to allow additional space for insulation. All of these measures do increase the energy efficiency of a stick-framed wall, but they also increase the cost by adding additional materials and increasing the labor required. Since labor is such a large part of the cost of a building, any additions that increase labor are particularly problematic.

There are other building materials that have energy efficiency advantages over stick framing. SIPs and ICFs are the two most common. Both of these materials are more energy efficient and both cost more than standard stick framing. The question is, where is the break point when modified stick framing costs as much as other, more energy efficient materials? ICFs are concrete filled foam forms. While ICFs are much stronger than other building materials, they are very different than traditional framing. SIPs on the other hand are a panelized wall system and are in some ways similar to traditional framing.

So for this discussion, I am specifically interested in a cost comparison between SIPs and stick framing of a structure with comparable whole wall R-values. At this point, I do not know of any non-biased studies to reference. But, I am going to research the question. I hope to be able to post some additional information regarding this subject in the near future.

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