The indoor air quality of the modern home is often discussed as if it is an improvement over the past — and in some important ways it is. The particulate and carbon monoxide burden of open-fire cooking and heating that characterized the indoor air of most human dwellings for most of history was a genuine and significant health hazard, responsible for respiratory disease, cancer, and shortened life expectancy that the ventilated, centrally heated, and mechanically filtered indoor environments of the developed world have substantially reduced. But the story of indoor air quality is not a story of linear improvement. It is a story of traded problems — the resolution of some hazards and the introduction of others — and understanding the full arc of that story is useful for designing the indoor environment with genuine clarity about what it needs and what it does not.
THE ANCIENT HOME: FIRE, SMOKE, AND BIOLOGICAL BURDEN
The first enclosed human dwellings — from prehistoric cave occupation through the earliest constructed shelters — shared a common indoor air quality feature: fire in an enclosed space with inadequate ventilation. The health consequences of chronic indoor biomass smoke inhalation are well-documented by the modern research on populations in the developing world where open-fire cooking remains standard. The particulate matter from biomass combustion is among the most harmful components of any indoor air environment, producing respiratory disease, cardiovascular disease, and lung cancer at rates proportional to cumulative exposure.
The biological burden of ancient indoor environments was also significant in ways that modern homes have largely resolved. Sharing living space with domestic animals — the standard arrangement in agrarian communities where cattle, pigs, and chickens were housed in proximity to or within the dwelling — introduced biological contaminants, dander, and the microbial load of animal occupation into the indoor air. Earthen and organic flooring harbored soil microbiome in ways that modern flooring does not, which may have had both beneficial (microbial diversity exposure) and detrimental (pathogen exposure) dimensions depending on the specific conditions.
THE TRANSITION TO COAL: A NEW KIND OF AIR PROBLEM
The transition from wood and biomass fuel to coal in the industrial era introduced a qualitatively different indoor air quality problem — the sulfur dioxide, nitrogen oxides, and heavy particulate from coal combustion, which replaced the wood smoke of previous centuries with combustion byproducts whose chemical complexity was greater and whose health effects were, in retrospect, severe. The coal-burning cities of the nineteenth and early twentieth centuries — and the coal-heated homes within them — produced indoor air quality that by modern standards would be unacceptable, with particulate and sulfur dioxide levels that drove the elevated rates of respiratory and cardiovascular disease documented in those populations.
The great fogs of London — the coal smog events that culminated in the Great Smog of December 1952, which killed an estimated 4,000 people directly and contributed to the deaths of an estimated 12,000 more in subsequent weeks — were the most visible manifestation of coal combustion indoor-outdoor air quality and were the proximate cause of the UK’s Clean Air Act of 1956, which began the long transition away from domestic coal combustion in the developed world.
THE MODERN TRANSITION: CLEANER COMBUSTION, NEW CHEMICAL COMPLEXITY
The replacement of coal with natural gas and oil, and subsequently with electric heating, eliminated the combustion byproduct burden from the indoor air of most modern homes while simultaneously enabling the construction practices that created a new category of indoor air quality concern: the sealed, highly insulated home.
The energy efficiency movement of the 1970s — driven by the oil shocks of 1973 and 1979 — accelerated the development of construction practices specifically designed to minimize air infiltration: vapor barriers, improved window sealing, insulation standards that dramatically reduced the exchange of indoor and outdoor air through the building envelope. These practices achieved their intended energy efficiency goals. Their indoor air quality consequence — which was not the focus of the energy efficiency optimization — was the concentration of whatever pollutants the indoor environment contained.
The materials that were being introduced into these increasingly sealed homes throughout the postwar period — composite wood, synthetic carpet and pad, vinyl flooring, synthetic textiles, plastic furnishings, and the cleaning and personal care products that populated them — were off-gassing into an indoor environment that had less and less ability to dilute their contribution through natural air exchange. The tighter the building, the higher the concentration of indoor-generated pollutants relative to any given generation rate.
THE PRESENT AND THE DESIGN RESPONSE
The modern home in the developed world breathes less than any previous human dwelling in history — by design, for valid energy efficiency reasons, with consequences for indoor air quality that are now well-characterized enough to design around. The design response is not to undo the energy efficiency gains of tight construction but to address both the source and the dilution problems simultaneously: reducing the indoor chemical sources through material selection, and restoring adequate fresh air exchange through mechanical ventilation systems that recover the thermal energy of the outgoing air while providing the fresh air intake that the sealed envelope prevents from occurring naturally.
The home that has been designed with both of these priorities — low-VOC materials and adequate mechanical fresh air exchange — delivers indoor air quality that no previous era of residential construction has been able to provide: genuinely clean air, in an energy-efficient envelope, with the biological comfort that adequate ventilation delivers. That is the current frontier of health-conscious residential design, and it is the environmental standard that House Remedy’s philosophy points toward.