We are trying out stick framing without thermal bridging and cellulose insulation to compare the costs, time to assemble and performance to SIPs. The SIPs have been very difficult to implement on our tight infill lots in Philly and we are not convinced they are the best method for us to build in the city. I think it would be a lot easier on non-rowhome houses without shared party walls.

We are no moving away from the Passiv Haus standards, simply the official certification. We are making educated guesses on insulation levels, windows and passive shading on the Skinny Project that will give us the most bang for the buck based on what we’ve learned. We will perform the Passiv Haus calculations during construction to see how far off we are, if at all. Based on what we learn, we will tweak our model going forward as needed.

The Passive Project was an educational project to learn how to build homes to the most stringent energy efficiency standard in the world. We have learned a lot from it, but have not determined as of yet if it is feasible or worthwhile to pursue the official certification on every home we build.

Why the move away from SIPs to stick frame construction with the skinny project? While blown cellulose may be good, SIPs are supposed to provide a tighter envelope – one of the most effective ways to reduce energy consumption.

We use blown cellulose on our commercial projects; I would recommend performing a thermal scan on the walls after the gyp board is up and the cellulose has settled (it’s not as expensive as it sounds). This will help identify/fix missed spots or ‘holes’ in the insulation, especially if you plan to use the dry application method.

Also, why the move away from the Passiv Haus standards? Too expensive, cost-benefit not making sense, foundation details too complicated? You commitment to building to those rigorous standards and selling the homes at that price point took balz.