I do agree with most of what has been said on this thread about superinsulation and its future. Even for those (mainly the women?) who may give priority to visible things like granite countertops over the invisible things, buried behind the walls, there is the appeal of a very, very comfortable house in a cold climate. I shudder to think of what some of those McMansions in a zone 6 climate must be like on a windy winter day.
Getting to superinsulation level in a new house isn't all that difficult, but it has to be well thought out at every stage of design and carried out well during construction. Most builders don't know how to get it right, but many are willing to work with the homeowner who has done his homework and learned what has to be done. It does help to be on site as much as possible during construction and to be on good terms with the crew.
Superinsulation involves insulation levels much higher than what code requires. As one builder puts it in his tagline, "Code is the minimum to pass. You build to code. Congratulations! Your grade is a D-." It also means air sealing well, to make for a very tight house. It's no surprise that the new air tightness standard for the Energy Star program calls for no more than 3 ACH (Air Changes per Hour) at a blower door depressurization to the standard 50 pascals. Actually, it's fairly easy to get significantly tighter than that. The heat it takes to warm up a given amount of cold air leaking in to replace warm air being pushed out is easy to calculate, and the result can be a surprisingly large fraction of a house's total heating bill.
Some builders still argue that you can't make a house too tight, that it "has to breathe." Well, the occupants have to breathe. The house has to avoid problems of excessive moisture getting into the exterior walls. Making a house tighter helps in that regard, but the inside air should not be allowed to get too humid. One of the first things learned from the first superinsulated houses is that the tightness that is part of the superinsulation design also leads to very high humidity inside, even in the dead of winter, unless fresh air is introduced in controlled fashion. As mentioned, this commonly is done in cold climates through the use of heat recovery ventilators, which are basically air to air heat exchangers.
The problem with trying to make a house "not too tight" is that there is no way to build it in a way such that adequate ventilation occurs all the time. All you know is that leakage is at its worst in bitter cold and windy weather, and then may be much too leaky for comfort and energy efficiency or still may be inadequate for human health and comfort. In mild and windless weather the leakage will be practically nothing. Worst, there isn't any control over ventilation rate in such a house, short of opening windows, which most folks won't do in winter. So it's not surprising that along with code changes requiring much tighter new construction, confirmed by blower door test, there also are requirements at least in some states for mechanical ventilation to provide ASHRAE section 62.2 minimum fresh air flow. I think Minnesota is one such state.
The cost of going to superinsulation level in new construction is not all that much. The number I see often is around 5% more. After all, it's only the outer shell that is changed. To be sure, sprayed foam is the most costly insulation, for a given amount of R value, although it does give a typically very tight outer shell. There are less expensive ways to get a tight house, though, and there are other websites out there that cover all such ways in considerable detail.
In our case, a 2010-2011 build (our retirement home in NH, climate zone 6), the shell is a double stud wall with a 12" insulation cavity filled with dense packed cellulose. That's an R40 wall. Loose cellulose in the attic, 18" deep, gives R60 there. The parts of the lower level walls that are concrete foundation are water proofed (not just "dampproofed") and have a 2" layer of rigid foam both inside and outside, from footing to sill. The above grade part of the exterior foam is protected with surface bonding cement troweled on. Inside the foam is protected by drywall, as required by code as thermal and ignition barrier. Below the slab is a double layer of 2" rigid foam and poly vapor barrier. So concrete walls and slab have R20 insulation on them. The windows are triple-pane, argon filled, low-E coated casements for the most part. Yes, those were expensive, a big part of the extra cost to go superinsulated. I think they are worth it. There is a noticeable difference at the inside of a triple pane window compared to a regular double pane window. The inside glass temperature is notably warmer.
The final blower door test, with range hood and woodstove ducting all connected, came in at about 0.8 ACH50, or about 0.04 ACH "natural" worst case air leakage. The energy start examiner said it was the second lowest air leakage he had measured, and number one was for a much smaller house.
One of the nice things about such a house is that selection of heating system almost doesn't matter, from an energy use point of view. The design load is so small that the system is going to be small, for whatever equipment is selected. In our case, since we were having a new well drilled anyway for water supply, we went with ground source heat pump (aka "geothermal"). The unit is a two-stage, two-ton model, the smallest that Climatemaster makes in its Tranquility 27 line. So far the unit has not gone to second stage operation and keeps the whole house comfortable without running full time.
We do have a small woodstove in the lower level, a Quadrafire Millenium 2100, with the outside air kit connected to a duct to the outside. This winter, our first in the house, we haven't used it too much, but I like to have a wood fire now and then. That little stove, with the glass door, looks so warming with the fire burning so hot and cleanly inside. We actually used that last winter to heat the whole house to mid-50s, running part time (mid afternoon to perhaps midnight), a temperature the crew found quite comfortable while they finished up the inside work. Quadrafire says that stove is good for heating 1,000 sqft.; this house is nearly four times that. The warmed air distributed nice and evenly throughout the house by itself. The up and down temperatures stayed within one degree of each other.
