Equitable sustainabilty on a planet with finite resources demands we greatly shrink our 'ecological footprint' - the amount of resources, including energy, consumed to provide for us. Domestic life accounts for a substantial part of this: our homes, how they are built, and how they operate. A recent (ca 1990) initiative in maximizing building energy efficiency produced a set of standards and building practices that came to be known as Passivhaus.
The reactive house will be Passiv, but not in the formal sense of meeting the requirements for Passivhaus certification. While there are various ways to meet the standard, it is primarily associated with using much greater levels of insulation than typical codes require (super-insulation), employing windows that also provide better insulation (often triple-glazed, etc), and ensuring a very tight air seal in the building envelope. Given such building airtightness, Passiv houses frequently need a mechanical ventilation system.
The reactive house embraces these techniques, because they are sensible means to realize energy-efficient living, as well as providing ancillary benefits of comfort (no drafts, cold surfaces, quiet, good indoor air quality, etc), and because there is an established market in products and building expertise that can be leveraged.
While the reactive house will draw on all these design and construction practices, it places little value on formal certification (with its added cost, inflexible interpretation), and primarily emphasizes the need for precise quantitative modeling and measurement of built artifacts.
Efficiency is only one factor in the total energy equation: another is scale/size. In fact, size has a multiplier effect, since increasing size mean that we first incur the initial embodied energy cost of the needed materials - the sheer amount of mined, harvested, manufactured, transported, etc (all energy-embodiments) stuff. But larger size also means a bigger operational energy budget for the life of the structure: more square footage to heat, cool, keep dry, etc. McMansions are the anti-pattern here - size matters. The reactive house will provide domestic comfort without wasteful resource use, and this means reexamining current norms.