Energy Considerations – Part Deux

Example of a 2x6 double wall construction from Taz Home Theater site.After a long verbal training session with Ryan Shanahan of Earth Advantage, it turns out that I should update my thinking concerning energy consumption. I’ve heard over and over again that contractors tend to overlook the efficiency that we are capable of building into our new high performance buildings, and Ryan assured me that I’m included in that group.

I was bragging that my floors with the electric NuHeat mats underneath the engineered wood flooring were going to be warm, keeping my feet happy. “Hold on bucko, you need to realize that if we do our job correctly, there’s not that much heat being called for in the building”. . . . hmmm. OK so maybe my floors aren’t going to be continuously warm after all.

Then I’m emphasizing the great looks of the Olympic Avalon wood burning stove, and its ability to hold a fire overnight. Wrong again, if this building performs as it should, the selected model will drive us out of the home with heat; nice problem to have. We’ve got to rethink to BTU requirements of this building aligned with the production of the stove.

Ryan now goes on to suggest I reconsider the NuHeat floor totally. He says that the ductless split heat pumps really are more efficient. The NuHeat mats are 100% efficient, BUT they’re still powered by electricity, whereas, the ductless split heat pumps, are grabbing the energy existing in the outside air. I like gaining that energy hanging around in the outside air already.

We’re going to probably go to an offset 2 X 6 double wall, rather than a single 2 X 6 hybrid insulated constructed wall, as shown in the picture by Taz Home Theater. If we can eliminate the thermal bridging of solid wood, as evidenced by the infrared images of buildings with a solid stud member, we’re ahead of the game. Plus the benefit of using less expensive insulation materials like fiberglass, rather than the cellular foams. My intension is to track closely how much more the double 2 X 6 wall runs, to get an accurate number for cost component on this alternative construction method.

I’ve never been a fan of the open air space method required for true rain screen exterior walls. We lose the cross sectional insulation additive advantage by introducing moving air flowing beneath the exterior siding, not to mention the potential of wavy siding applied to the spaced battens. Apparently, we get points for extended overhangs, and their protection of the wall, without having to add a layer of air flow, thus reducing the thermal advantage of the entire wall. At the same time, reducing the need for air conditioning, due to blocking summer solar gain.

So the true R values for this home should be R-40 walls, R-40 floors and R-60 lids, not to overlook the windows performing at .20 U-value or less, sounds like triple glazing to me. We will probably need a photovoltaic system at somewhere between 3 and 5 KW in parallel connection, with individual inverters at each panel. And a whole house heat recovery unit, ventilating this whole structure for fresh air.

I’m so thankful that I’m surrounded by the best in the business, not because they are just good at what they do, but because they make me think twice – thrice – about every idea I have, helping me to build the best home for the Pacific Northwest weather and temperatures.

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