In our culture we have a tendency to look for new technologies that can make it easier for us to do things the same. The topic of sustainability and mitigating our effect on the environment suffers from this more than most despite the fact that the real opportunities for sustainable progress will come not from gadgets and gizmos, but a behavioral shift. Technological advancement can help us gain a bit of ground and buy us some time, but no matter how hard some innovation strives to keep the status quo intact, the realm of unexpected repercussions can be unavoidable. Our reflex needs to shift from assuming we can operate without change to one of automatic reassessment.
Over the course of modern American history we have continuously improved our ability to separate our homes from the natural environment. The exterior envelopes of our buildings can now be tighter and more efficient than ever, bringing opportunities to reduce the amount of energy and resources needed to heat, cool and clean the places we live and work. This evolution is positive in many ways, but the culture of how we build space doesn’t necessarily evolve as fast as the walls around it. Having a super tight–even airtight–envelope can bring some drawbacks if our building practices don’t evolve to respond to a new set of functional realities.
Walls and Where We’ve Been
Not that long ago, we counted on the skins of our building to focus on the heavy lifting when it came to protection from the elements. If four walls and a roof could basically keep us warmer and drier on the inside than it was on the outside then things were working as well as we could hope. Turning up the heat meant putting another log on the fire and even then the ability for heat to radiate through open space was limited. All one could do was flood a space with heat and huddle close. Even with a roaring fire in the hearth we did not have great ways of keeping the warmth inside with the absence of insulation. Our greatest ally was a thicker wall. Adding some extra layers of clothing often made up the difference.
When it came to the finer points, a lot slipped through the cracks; a lot of air. The standard of double hung windows (wooden sashes in wooden tracks) were functional though far from efficient. Plates of single-paned glass served as a weak buffer for temperature differences on either side and air easily found its way between the components, especially after the house aged and seasons caused the windows to expand and contract with the weather. The seals (or lack thereof) around doors provided additional points of infiltration. Though homes kept the gusts out, drafts were a common occurrence. Even with the invention of steam radiators and eventually forced hot air, we had ways to focus heat on windows and doors in spite of–not in lieu of–their drafts.
But in hindsight, a drafty house wasn’t all bad. For all of the years that fireplaces provided heat for homes, they are still a rather inefficient way of heating space with most of the heat going up the chimney (they’re like old coal-fired power plants like that). This can put a room under negative air pressure with the heated updraft in the flue pulling air out of the home and the smoke up with it. Without drafts, fireplaces would have needed more direct sources of supplemental makeup air (as many have today).
Fast Forward to the Age of Modern Living
We have come a long way since then. Our windows and doors are now usually double, if not triple-glazed with gaskets and sweeps that minimize ability for air to move through these punctures in our facades. Our insulating materials can increase thermal protection of a wall twenty-fold from what it was a century ago and where the smallest of cracks remain, the advent of caulk and sealants can fill the gaps for a completely fortified exterior skin.
For as efficient as a tight envelope can be, however, a little fresh air can do us some good. These days, materials like spray-foam insulation can make a house so tight that natural air circulation no longer reaches all of the spaces inside if the doors and windows are closed. Without the drafts that used to be par for the course the air can become stale.
Stale air alone may be a minor inconvenience, but a super-tight skin also means that anything lingering in the materials of the home stands a much higher chance of lingering in the air. An envelope good at keeping nature out is just as good at trapping things in. As a result, issues of indoor air quality become only more important. Materials like varnishes, sealants, fabric preservatives and paints traditionally off-gas over time, releasing components into the air such as Volatile Organic Compounds (VOCs). The chemicals used to promote durability in materials are not always the best for us to be inhaling and can lead to illness given enough exposure. It can take four to five years for things like paint, floor finishes or carpets to finish dumping chemicals into the air.
These days, we often have numerous mechanical devices that exhaust air from a building. Kitchen hoods, bathroom fans and heating and cooling equipment all push air out of the envelope, but air that is pushed out needs to be replaced. Nature insists upon path towards equilibrium, continually oscillating around a point of statis. Both air and moisture move in pressure differentials, migrating from high to low. Like the former reign of the hearth, these components can put a space under tremendous negative pressure with a stronger facade forbidding the equalization of pressure on either side that once happened due to the inherent limits of the construction.
Ultimately, the space inside can become a vacuum, pulling water vapor through whatever cracks it can find until it finds a place to condense inside the house, or worse yet, inside the walls. Combined with air conditioning (also a relatively young cultural norm) mold growth can follow with health risks shortly behind. Once upon a time, the air rushing through the wall would inherently help not only balance the pressure, but dry out the wall construction and help discourage mold growth.
So What’s the Answer Smart Guy?
All of the technological prowess that fortified our walls can also work to make sure we use them wisely. Mechanical systems need to be balanced with fresh air intake to provide regular cycles of cleaner air. The best way to do this is by incorporating an Energy Recovery Ventilator or ERV. These great devices take the air being exhausted (that energy has already been used to heat or cool) and uses it to pre-temper the fresh air being pulled in. ERVs can serve as a central hub for all bathrooms exhaust fans and use timers to regularly rotate air in the house. It’s not that this kind of coordination is difficult as much as it may be less commonly implemented. When buying or building a house without an architect, it doesn’t hurt to make sure someone on the mechanical side is running new calculations to balance out your home.
Given that we are so good at keeping air in, we should start by making sure that the things inside the house are only things that should be there. Put another way, leave as many of the chemicals out as you can. The use of Low-VOC, or better yet NO-VOC, paints and sealants can make a large difference indoor air quality and building health over time. Try and leave out pressure-treated lumber wherever possible and look for engineered wood products, like plywood, that do not contain urea-formaldehyde.
Promoting innovation is important, but the looking ahead to the creation of new means and methods has to include a glance backwards to see what other things may have to change as a result. Like everything else, sustainability cannot be thought of in terms of absolutes. The belief that “tighter=better” is not incorrect as much as incomplete. As a broad stroke it misses the fact that there is more to the quality of an indoor environment than the integrity of the thermal enclosure. The problem we face today with residential construction is that we have gotten too good at making a super tight envelope but not good enough at coordinating our systems to match.
Instead, we may want to ask ourselves if we cause more problems than we solve by trying to over-temper interior environments. It’s easy to forget that it was not long ago when we didn’t have air conditioning and somehow we all survived. What is the threshold or conditions for when some over lap between interior and exterior is preferable to a hermetically sealed chamber?
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