The Ideal Wall

                                             The Ideal Wall

The search for the Ideal Wall system is the Holy Grail of the sustainable building
movement. We’ve optimized residential construction for a long time now for cheap,
abundant energy, and for disposability. With that energy finally vanishing, our first-
pass approach is to adapt the same HVAC technology to a high-tech shell. This
approach dismisses thousands of years of research on sustainability, building
materials, and human comfort.

I believe that all the pieces for an optimal wall system – combining old and new
technology – now lie before us, unrecognized for what they could be: compellingly
comfortable, energy efficient, esthetically pleasing, and resource wise. I also believe
that the main barrier to its widespread adoption is that it has yet to be assembled and
shown to consumers.

As a culture, we seem to have forgotten how to achieve in our homes the sort of
comfort that we talk about. Window seats and yard-size bedrooms photograph well,
but rarely provide the experience suggested by the accompanying text. Journalists
don’t mention that sitting with your backside to glass is uncomfortable for all but a few
days of the year, or that sleeping in a cavernous room is downright agoraphobic.

Thermal mass provides the comfort people seek. I feel its importance for both
efficiency and comfort in homes is currently under appreciated. It’s not a coincidence
that mammals, reptiles and plants all appreciate radiant heat more than the convective
variety; given a choice, a cat will nap in a sunny window sill, but not in front of hot air
register. Thermal mass is important to optimal performance and comfort in all
dwellings because it’s the storage and re-transmission medium for radiant heat.

The significance accorded to thermal mass seems to be at a low. Thermal
mass appears to be associated with passive solar, which has fallen out of
favor for the new paradigm of the day: construct a house that performs like
a Styrofoam picnic cooler, downsize the HVAC system, and pave the roof
with a massive, expensive solar array. What was once considered the ugliest
part of a residence, the electricity meter, is now the sexiest: to the delight of
those with the money to pull it off, it can be made to run backwards.
What does this do for sustainability? The manufacture of solar panels is not
without environmental cost. At the moment, they’re made from semiconductor
-grade silicon, whose manufacture uses huge amounts of energy, toxic
chemicals, and ultra pure water. The blind rush to rooftop photovoltaics
without looking at the bigger picture of sustainability takes us two steps forward, and
one step back.

Problem: the Empty Fridge

The Well-Stocked Fridge

The equivalent of a full refrigerator is a home with sufficient thermal mass. In coastal
California and Oregon, and other climates with mild winters and/or significant
temperature swings between day and night, the benefits of insulation, even the super
insulation provided by straw-bale and SIP construction, are modest compared to the
combination of thermal mass and passive solar heating. I’ve seen a number of
otherwise uninsulated structures that never fell below 50 degrees Fahrenheit, or
above 75, in temperatures ranging from 10 degree lows to 115 degree highs.

My point isn’t to dismiss the importance of insulation. I have also been in old, thick-
walled, uninsulated stone homes in Switzerland that never became truly warm, that
managed to serve as infinite heat sinks for countless cords of firewood. Without a
doubt, most climates require insulation. And there is definitely such a thing as too
much thermal mass.

The Ideal Wall for most climates should have both mass and insulation. In other
words, the Ideal Wall should resist air infiltration, provide a path of low thermal
conductivity to the outdoors, and provide thermal mass to stabilize indoor
temperatures.

Arguments for and Against Mass Walls

I’ve found few architects or building scientists who dispute this, at least in principal.
The point of contention seems to be that the combination of mass and insulation is
difficult to implement. Therefore, they argue, various technologies favoring one over
the other are most appropriate.

For example, Bill Chaleff, a SIP proponent who has penned a number of great
whitepapers, defines thermal performance purely in terms of insulation and air
infiltration. In his paper “SIPs 101 – for Martians!” (http://www.sipweb.
com/monitor/bc_4.2005.asp), he compares different wall systems against 13 criteria.
Against “thermal performance”, SIPs score highest, and masonry next to lowest. Yet,
clearly, he’s aware of the role of thermal mass in building, as he has a good paper on
passive solar and plenum-heated mass floors. It’s unclear whether he believes
thermal mass is only needed in passive solar design, and/or whether it should be
implemented in floors.

Under most circumstances, if you have to choose between putting mass in a wall or a
floor, the floor is a better choice: the floor presents a better target for sunlight for
passive solar gain. My point is that mass in the floor and walls provide superior
comfort and temperature stability. Also, with mass in the walls, it’s possible to do
without the mass in the floor, or impair it to a greater extent with a wider range of floor
finish options.

An argument I often hear against mass walls is that they are too thick: they waste real
estate. If interior space is so precious, why do we have so many unconditioned
attics? I don’t buy it. An enduring, high-performance wall system is as legitimate a use
of a building’s footprint as any that I can think of.

The a common argument I hear against mass floors is that concrete slabs are too hard
underfoot. I’d like to point out that slabs don’t have to be concrete: soil-cement and
adobe both make for warmer, softer, medium-wearing floors. Needless to say, many
other options exist. Once again, if you have mass in your walls, you don’t need it in
your floor.

Given the extra expense, a super-insulated mass wall is a hard sell on technical merit
alone. It’s the comfort they offer that most strongly differentiates them, but people
need to experience it firsthand.   I am confident that if examples of super-insulated
mass walls were more common, this paper would be unnecessary.

Perhaps you are one of the many people who’ve never had the opportunity to visit an
occupied adobe building in the winter. So, if you will humor me for a moment, swap the
seasons. Imagine and compare walking around in a large commercial building, say a
Costco, in the heat of summer. Now imagine that, on the same day, you’ve just
entered a winery. Think about Costco’s large, shaded slab -- nice and cool underfoot,
right? But think of the winery: that sense of cool is three-dimensional. (If you’re also
thinking about all that chilled wine, so much the better.)

If you haven’t had any of these experiences, then even this thought experiment was a
failure. In that case, I’d ask you to take my word for it: the trouble of putting mass and
insulation in walls is worth it.

Uninsulated mass walls abound. Unfortunately, attempts to replicate them in climates
without adaptation and insulation have led to the erroneous belief that mass walls are
unsuited to most climates, when quite the opposite is true. I would argue that the only
reason not to consider them would be for buildings that are of such a temporary
nature that the copious use of energy seems like an acceptable remedy for their
deficiencies. (Does this sound like the rationale for our current housing stock?)

Current Wall Systems with Thermal Mass

I’d like to mention a couple of wall systems that combine mass and insulation, and how
they do vis-à-vis thermal performance -- that is, the version that considers the
importance of thermal mass.

Insulated concrete form (ICF) systems sandwich concrete between split layers of
insulation, usually closed-cell foam. This is less than optimal for both insulation and
thermal mass, because the half of the insulation is between you and your thermal
mass, working against you. Some specific products merit being mentioned by name.
Durisol™, made from mineralized wood pulp/cement, is a filled cavity masonry unit that
biases the concrete mass in the block towards the living space, and adds a thin
blanket of mineral wool between the mass and the outside of the block. In my opinion,
that’s a sensible layout. Rastra™ (foam/cement) is a hybrid ICF/masonry unit that
splits the slightly insulative block material with the concrete fill (the structural/thermal
mass.)

Rastra literature would have you believe that ICFs and high-tech masonry are a low
embodied energy building system. While the grid structure of the resulting cores
makes efficient use of the concrete, it’s still a high-embodied energy wall system that’s
not easily recycled or reused. Apparently the embodied energy in the concrete fill
lands on someone else’s tab. Neither of these two systems gives you an R-value
better than about 12. Based on R-values for closed cell foam, regular ICFs fall in the
range of 15-25.

SIPs. Their superior conductive and air infiltration resistance, not to mention their
efficient use of materials, makes for an ever-growing school of converts. Combined
with slab floors or other mass, they produce a space that performs pretty well. My only
beef is that, in common use, there’s no mass: they produce the perfect empty
refrigerator. That said, and at the risk of getting ahead of myself, I feel that they are a
critical component of an Ideal Wall.

Straw Bale. I consider straw bale to incorporate thermal mass because it requires
interior plaster anyway; that plaster can be built-up to any depth. Arguably, it’s the
greenest super-insulator of all time. It’s challenges include the fact that it’s not really
structural, it’s highly vulnerable to water damage during construction and throughout it’
s life, (necessitating first-time-perfect water detailing) and it eats up the most real
estate of any wall system. Nevertheless, from a sustainability standpoint, an Ideal Wall
based on straw bale and earth is topic worthy of a future paper.

Natural Stone. Due to the lack of uniformity of natural stone, it will remain forever
labor intensive. Proposals I’ve seen for insulating natural stone, like stacking it against
an interior SIP wall, give up the benefits of its thermal mass. Of course, stacking it
against two faces of a SIP wall yields a very durable, attractive, and expensive wall of
modest embodied energy (if locally sourced) with at least average moisture
performance. (Stone walls can wick water, and thus offer minimal protection to the
OSB SIP faces.)

Faux stone. “Cultered stone” is a veneer made from concrete, and as such, is a high-
embodied energy product. As it offers minimal mass, its function is largely decorative.

Cast Concrete, and Concrete Masonry Units. Readily available and easy to work with,
composite concrete walls systems that incorporate rigid foam are available. In my
opinion, despite their longevity, the energy required to manufacture cement and
transport the materials rule out these systems as sustainable building materials in
single-family and low-density housing.

Other Properties of an Ideal Wall

In the introduction, I said that the Ideal Wall uses something old and something new.
Before I tell you about it, I have to justify the “something old” part. Listed below are an
aggregation of desirable attributes drawn from many different materials.

As I see it, the exterior portion of an Ideal Wall should
•     last a really, really long time -- 300 years, at a minimum
•     block entry of liquid water as much as possible
•     allow any liquid water that does enter to drain and/or escape as vapor
•     be easy to repair
•     not feed, shelter, or provide passage for insects and microbes (fungus and mildew)
•     self-heal cracks and other minor thermal/moisture trauma

The interior portion of an Ideal Wall should
•     provide for a range of finish options
•     buffer and release water vapor, without condensing it
•     facilitate installation and modification of utilities: electrical, water, sanitary, and gas
•     facilitate the mounting of cabinets

The wall system as a whole should
•     be easy to build and require nominal trade skills
•     provide great tensile, compressive, and shear strength, and stability in seismic
events
•     fail gracefully, rather than catastrophically, when stressed by loads and moisture
•     facilitate installation of doors and windows
•     provide anchorage for interior walls and suspended floor systems
•     use minimal energy in production and transportation
•     reuse or recycle easily, or decompose gracefully under specific conditions not
encountered in normal use

Earth, the Miracle Material

When people think of building materials, earth doesn’t usually come to mind. In fact,
most people confuse earth and garden soil. Earthen building materials, which include
cob, adobe, and rammed earth, are actually similar to concrete. (For simplicity, I’ll
sometimes refer to all of them generically as “adobe”.) In each case, a binder coats
and binds particles of aggregate. Sometimes reinforcing fiber is added for tensile and
shear strength. “High-strength” sack concrete achieves its strength through the
addition of glass fiber; adobe, straw or manure. Clay, the binder in adobe, is weaker
than cement because it cures through dehydration. Significantly, unlike cement, clay
has no inherent energy associated with its manufacture. Through careful formulation,
compressive strengths of up to 2000 psi are possible without additional binders [http:
//en.wikipedia.org/wiki/Compressed_earth_block]. This far exceeds the design
strength of ordinary mortar (1500 psi), and is close to standard 5 sack concrete.

Another common misperception is that building with earth is like using ice blocks for
igloos: that it’s a material with a very narrow range of application. The truth is,
worldwide, there are more homes built of earth than any other material. Earth is used
extensively, and often exclusively, in cultures where labor is less expensive than other
natural resources. And while it’s true that it’s most common in desert climates, you can
find examples worldwide, in very wet and very cold climates.

Ironically, it’s used extensively in the areas of the world with the cheapest oil. Factors
other than climate appear to influence the use of other building materials over earth.

I suspect the real reason earth doesn’t get the respect it
deserves is that it’s “common as dirt.” As they say,
familiarity breeds contempt. I’m asking you to forget what
you might know about the material for a moment, and
pretend that it’s high-tech, new, exotic, and expensive –
whatever sexy quality that piques your curiosity. Below,
case by case, we’ll consider how earth-based building
materials fair against the wall criteria listed above.

Useful life. When protected from wind-driven rain by appropriately maintained lime-
based stucco, a roof with overhangs, and a foundation that prevents the base of the
wall from being saturated, earth walls last forever. In Devon, England, a place with a
maritime climate (plenty of wind-driven rain) and a history of earth building, there are
many 300-year-old, multi-storey houses. In Yemen and other dry regions where
neglect has less of an effect, there are 900 year-old, 9 storey buildings. Earth
buildings last as long as people want them to. Excellent.

Blocks entry of liquid water. As I said earlier, clay is the binder in earth-based building
materials. Clays are expansive to varying degrees. The expansive nature of clay
causes it to become increasingly water repellent as it gets wetter. Consider that the
most expansive of clays, bentonite, is the active ingredient in kitty litter! Due to the
generally capillary nature of aggregates, the overall performance of an earthen wall is
not quite as good as that of a pure clay wall. (Note: a pure clay wall would be
undesirable for a host of other reasons.) Good.

Allows any liquid water that does enter to drain and/or escape as vapor. As much as
clay is water repellent, it is vapor permeable. Provided it is protected from complete
saturation, clay responds to vapor pressure and equalizes with its surroundings
relatively rapidly. Excellent.

Is easy to repair. By thoroughly rewetting a clay surface, new material can be added
to achieve a chemical bond, not just a mechanical bond. Repairs achieve the strength
of the original material. This is not the case with concrete. Excellent.

Does not feed, shelter, or provide passage to insects or microbes. As mentioned
earlier, earthen building materials contains aggregate and a binder. As is the case
with concrete, insects derive no nutritive value from either, and have great difficulty
tunneling through the matrix. Similarly, with its relatively high vapor permeability, earth
desiccates microbes, plants and sprouting seeds. Excellent.

Self-heals. When earth is rewetted, the clay mobilizes and bridges small cracks and
fissures. This is not a common attribute in other building materials. Good.

Provides for finish options. Against this criterion, earth has strengths and
weaknesses. The evenness of the surface is a function of the construction method
(for example, rammed into full-height forms, versus stacked in irregular masonry units,
versus wet-hacked roughly plumb with a machete.) In general, the surface does not
compare well with drywall. It does accept screws, so drywall can be fixed to it. Since it
doesn’t exhibit water expansivity to the extent that wood does, natural (vapor
permeable) paints and plasters bind well. Non-vapor-permeable finishes can cause
serious problems if the entry of liquid water is a possibility. Average.

Buffers and releases water vapor, without condensing it. Earth can store a
considerable amount of water vapor without adverse effects. When the vapor
pressure reverses, vapor is re-released from whence it came. The net effect is
relative humidity stabilization, a very positive contribution to indoor air quality.
Excellent.

Facilitates installation and modification of utilities: electrical, water, sanitary, and gas.
Earth can encapsulate utilities, but it’s generally a bad idea. Retrofitting earth walls to
accept utilities is difficult in the best of cases. SIPs are electrical-friendly, with their pre-
fabricated channels, but my understanding is that you can’t (or shouldn’t) put plumbing
in them. Masonry and straw bale suffer from the same problem. Stick framed walls
are the friendliest in this regard; pretty much anything goes. Average.

Facilitates the mounting of cabinets. Earthen walls have some screw-holding
capability, but screws cannot be driven repeatedly into the same holes or the holes
tend to crumble and widen. Average/Poor.

Degrades or decomposes minimally in normal use. Earth degrades through only one
mechanism: erosion. If protected with breathable plaster, earth will not erode. Earth
can tolerate wetting up until the point of near saturation. If allowed to dry slowly, it will
suffer no damage. Excellent.

Is easy to build, and requires nominal trade skills. Compressed earth blocks (CEBs),
like those produced by the Cinva Ram [http://www.sanco-bg.com/Adobe_Block_Press.
htm], are highly uniform in length and width, and within ¼” or better in height. Using
½” earth mortar joints, they’re both a precise and forgiving system. Cast blocks have
greater variation. Headers can be wood, reinforced concrete, or channel iron.
Rammed earth requires specialized form building skills, similar to poured concrete
walls. Headers and the requisite bond beam are reinforced concrete. Cob is perhaps
the hardest of all to work with, given that it is free-sculpted, but it is also the most
flexible. In all these systems, window and door installation, addressed below, is
complicated. Poor.

Provides great tensile, compressive, and shear strength; stability in seismic events.
Pure adobe earth, and rammed earth, are very similar to low-sack concrete. It ranges
from about 300-2000 psi, depending on the shape and composition of the aggregate.
Additional strength and stability can be achieved by adding additional binders like fly
ash or cement. Without reinforcing fiber, compressive strength is good, shear
strength and tensile strength are not. Cob, which has added long straw fibers, has
significantly improved shear and tensile strength. Given the weight of the material, its
strength-to-weight is low to medium. Poor.

Fails gracefully, rather than catastrophically, when stressed by loads or moisture. Dry
failure of unfibered adobe is similar to that of unreinforced masonry. Rammed earth
usually has rebar in it, making it behave more like low-sack reinforced concrete. Cob,
with embedded straw fibers, fails gracefully under extreme loading of all sorts. Without
stabilization, when subjected to moisture, earth-based building materials fail
catastrophically when they reach saturation. Again, up until that point, they suffer little
or no damage. Saturation can occur when (a) the wall sits in standing water, (b) when
a watertight plaster is applied, or (c) a horizontal surface is exposed to weather,
facilitating ponding. For all but the very wettest of climates and flood plains, these
conditions are easily avoided through good design. Stabilized earth (stabilized
through the addition of cement, motor oil, or proprietary, biodegradable formulas) is
even less prone to weathering and failure. Average.

Facilitates installation of doors and windows. Installing doors and windows in earth
walls is similar to installing them in thick masonry walls. Anchorage requires
installation of additional materials, like a wood frame. Sill pan flashing must be carried
through to the outer surface of the wall. Most window installers become confused.
Poor.

Provides anchorage for interior walls and suspended floors. Interior walls can be
lagged into earth walls, but as mentioned under “cabinets”, screw holding capability is
mediocre. Anchoring suspended floors, particularly in a remodel situation, can be a
real challenge. In new construction, the wall usually steps in at each floor, and a
wooden ledger is leveled in mortar to support rafters. Posting up is an easier
solution. In a retrofit situation, if posting up is not acceptable, this can be a real
challenge. Average/Poor.

Does not wick water. Earth walls don’t move liquid water. Good.

Uses minimal energy in production and transportation. All forms of earth walls can be
made with 100% hand labor and zero embodied energy. Realistically, assuming
mechanization and locally sourced materials, energy use is low. Suitable soils are very
common. Where the sand/clay ratios are inappropriate, usually both sand and clay
can be locally sourced and formulated. Without a doubt, it is the greenest of all
building materials by weight, area, or volume. Excellent.

Reuses or recycles easily, or decomposes gracefully under the right conditions. If
stripped of a protective roof, in time, earth walls will erode and disappear. Adobe
blocks are easily reused. Excellent.

What can we conclude from all this? Earth as a building material has a number of
strengths that make it the greenest of all building materials. It also has glaring
deficiencies that must be at least partly responsible for its lack of widespread adoption
in the western world. Simple earth walls score poorly for finish options, ease of
anchoring cabinets, installation and alteration of utilities, installation of windows and
doors, shear strength and stability in seismic events, and familiarity among western
tradespeople. They also do not provide sufficient insulation in hot-humid or
continuously cold climates.

Letting the Cat out of the Bag

But what if we create a composite wall system by sandwiching something else between
two layers of earth? That something else should be an excellent insulator, and
contribute the missing shear and tensile strength. It should have excellent screw/nail
holding capabilities. It should accept windows and doors in a straight-forward manner,
and provide regular carpenters and other tradespeople with a familiar point of
reference. Finally, it should have integrated conduit for wiring, at least. Sound
familiar? We’re talking about SIPs, of course.

The Ideal Wall is a SIP wall sandwiched by adobe block (ideally, CEBs). The CEBs on
the outside of the wall are there to protect the SIP for all of eternity. On the inside,
they provide thermal mass and regulate humidity.

Prescription

Assemble the building like this: pour an extra-wide stem wall foundation. Then pour a
slab; this could be a grade-level or suspended slab. Alternatively, for a low-mass
floor, build a suspended floor over a gravel-lined, sealed, conditioned crawlspace.
Build the SIP wall at the center of the stem wall. Frame an unvented roof, apply roof
surface, and seal it to the SIP walls. Note that wind uplift isn’t a concern if the roof is
securely attached to the SIP wall; the huge weight of the CEBs hold the SIP wall down
for all of eternity.

Install special tack-welded window sill pans with self-furring plaster lath so that you can
later field-cut them at the edge of the CEB wall. Install the windows and doors. Pre-
pierce the SIPs at an engineer-specified layout (modulo the block height.) Now stack
the interior and exterior CEBs to within a block modulo of the roof, through anchoring
courses on each side with extra-long masonry ties at horizontal mortar joints according
to your layout.

Use a wooden belly board to close the architectural gap. Stucco the CEBs with lime
plaster, or, with sufficient overhangs and for a purist look, leave them plain.

Note: since it requires a long, damp cure, lime plaster is more tempermental to apply.
But unlike cement stucco, lime never needs replacement – just maintenance and
repair. This is because lime, like earth, continues to mobilize calcium, making it self-
healing. This same deposition mechanism forms stalagtites in caves.

Rough Electrical, Plumbing, and Finish: the Harder Part

Adobe’s harshest critics complain about these areas in particular. I expect it’s
because their point of reference is stud walls. Actually, the rest of the sequence for
new construction isn’t that challenging.

Cabinetry, fixtures, wiring – in new construction
Attach wooden frames of the same dimension as the CEBs (“gringo blocks”) to the SIP
faces and build them into the CEB course work. These anchor interior walls, cabinets,
additional floors, and so forth. Alternatively, the wall system won’t suffer if you stop the
CEBs for appropriate wall sections, like kitchen, bath and other areas requiring built-
ins. This allows you to recess cabinetry into the wall by a full block width (6-8”),
making it less obtrusive. Run wiring through the SIP panel walls normally, and bring it
to the wall surface through gringo blocks (which also serve for mounting switches,
outlets, and other fixtures.)

Floor support
Posts are the simplest support for suspended floors. Attach posts directly to the SIP
wall and integrate with the inner CEB wall, or leave them flush to the block surface and
through-screw them into the SIP panels in a retrofit situation. Alternatively, you can
suspend floors from the top of the sip wall/roof system – with wood, cable, or chain –
and through-lag through the interior block and both SIP panel faces. Another
interesting possibility is the use of a custom, adjustable height bracket, one with a top-
hanger flange that could be tapped into a notched mortar joint, and through bolted
with a long panel screw through both faces of the SIP. Let me stress that all but the
post-recessed-into-the-wall are just ideas; they need input from an engineer.

Plumbing
It’s my belief that plumbing shouldn’t be run in the exterior wall system. As in SIP
buildings, run plumbing up through the floor directly, or inside interior wet walls.

Remodeling
Since I am strongly influenced by Stewart Brand’s book How Buildings Learn, I prefer
to think of new construction as a special case of remodeling. This keeps new
construction greener — both by extending the building’s useful life, and minimizing
waste during subsequent remodels.

Tentatively, the scheme I envision for switches, outlets, and small fixtures works like
this: on layout for the SIP prefabricated channels, hammer-drill a hole large enough to
fit ¾” conduit through the CEB and to the first SIP face. Continue the hole with a spade
bit until it reaches the channel inside the SIP. Cut an area slightly larger than the
fixture and centered on the hole with a grinder. Run wiring through the SIP and bring it
to the surface. Slide a length of conduit over the wire and tap it through the CEB and
into the SIP. Attach the fixture to the conduit and foam it in place with aggressively
expanding foam.

Mount cabinets by grinding out a horizontal, shallow area and filling it with a screw-
friendly filler. This serves in lieu of blocking. For further tear-out strength, drive and
leave protruding screws before applying the filler. Alternatively, leave out a section of
CEBs, so you can recess the cabinetry and affix it directly to the SIP. To stabilize a
long run of wall compromised by such a break, add king studs as needed, screwing
them to the block ends.

Add additional floors as before: by posting, suspension, or possible hangers plus
through-bolting.

Conclusion

Combining two earth-friendly wall systems – one of the oldest in existence, and one of
the newest – yields a hybrid system with superior insulation, superior thermal mass,
superior moisture management, superior durability, and – most important to the
consumer – superior comfort.

I hope that the solutions to the challenges posed by this system prove it feasible and
worthwhile. If several houses can be built and demonstrated, new clients can be
attracted, educated and served. Most importantly, with input from a larger community
of architects and builders, barriers to greater adoption – the costly and unconventional
aspects – will go away.

By lasting at least five times longer than the houses currently being built, by
consuming less energy and fewer natural resources during its construction, and using
far less energy during its lifetime, each such house can make a leveraged contribution
to a better quality of life for us, and future generations.My point isn’t to dismiss the
importance of insulation. I have also been in old, thick-walled, uninsulated stone
homes in Switzerland that never became truly warm, that managed to serve as infinite
heat sinks for countless cords of firewood. Without a doubt, most climates require
insulation. And there is definitely such a thing as too much thermal mass.

Common misperceptions about adobe are that seeds sprout in
it, microbes thrive in it, and that it composts any wood and other
cellulose in close proximity. The opposite is true: earthen
building materials tend to “mummify” other building materials. By
blocking air and liquid water, embedded material desiccates and
stabilizes. Seeds quickly abort; wood is protected from large
humidity swings and insects; straw remains bright for hundreds
of years. By contrast, concrete, with its water-wicking
tendencies, does tend to rot anything it touches.

I like to call a super-insulated house, heated with forced air, and
otherwise lacking thermal mass, an empty refrigerator. Refrigerators
only achieve their rated efficiency when they are kept full. An empty
refrigerator cycles on and off, chilling the air inside, only to lose a
portion of the cooled air each time the door opens. Similarly, even in
a home with heat recovery ventilation (HRV) or energy recovery
ventilation (ERV), regular events -- like entry doors being opened
and closed, and exhaust fans for bathrooms and ranges running –
flush energy from a home.

Indoor Air Quality 1