Many of the principles enunciated so far concern energy: minimizing, locally sourcing, decarbonizing, etc, and wise energy use is doubtless a major pillar of sustainability. But it is not the only pillar. Our houses are homes for living beings, situated in a living environment. Current home building and living practices can be highly destructive to the environment, and harmful to inhabitants. The reactive house is salubrious in the broadest sense - it should promote the health not only of occupants but of the ecosystem in which the house resides.
The reactive house will seek to identify hazardous materials and wasteful practices and embrace alternatives; it will minimize earth harm in construction and use. Some examples: avoiding toxic building materials such as those enumerated in the Living Future Institute's Red List. Current building practices typically involve extensive disturbance of the site, removing trees, topsoil, etc. How much of this is necessary?
We live in a way increasingly removed from natural place and material: interacting primarily with manufactured, artificial, processed goods, foods, living spaces, etc. Whatever benefits these have realized, our knowledge of the risks and costs of such transformations has not kept pace with the changes. We are only recently realizing that well-intended (or convenient, or cheap) interventions have unacceptable outcomes: e.g. that the flame retardant chemicals we required for safety in our goods may be carcinogenic, neurotoxic, or endocrine-disruptive in the waste stream.
Our homes are where we spend the most time (so the effects of IEQ are greatest), and where we have - or should have - the most control. The reactive house leverages current scientific understanding to promote best quality environments, and where such understanding is lacking, relies on the 'precautionary principle' that prefers natural materials over those without a track record.
It is common to focus on air quality - which is of paramount importance, but the reactive house takes a much broader perspective on healthy indoor environments, and includes lighting (where the benefits of natural light are becoming more apparent), sound, odor, vibration, etc.
The reactive house expands the perimeter of concern beyond the walls of the house to encompass the entire living area, which includes outdoor spaces, passages, etc. The lawns our children play on can have as great an impact as the living room floor, and the outdoor environment has many more inhabitants than people whose welfare must be considered.
Finally, the reactive house will critically examine the notion of healthy living. For the vast majority of human history, comfort has been a reasonably good proxy/signal for well-being: if food tasted good, it was likely nutritious or beneficial; if our house was warm and dry, it meant we could worry less about rodent incursion and the like, since the building envelope was sound. But that equation has shifted in modern times.
Just as fast food can appeal to our taste yet lack significant nutritional value, so can we build homes for occupant comfort or ease that adversely affect well-being. One example: we directly attach garages to living spaces, and allow gasoline fumes, and other chemicals stored in the garage an easy path to the indoor airspaces - all in the understandable desire for convenience. Or maybe the upright toilets we use cause hemorrhoids or other conditions, and well-being would be better served by squat fixtures used elsewhere in the world.