ASHRAE Journal - January 2023 - 28

COLUMN BUILDING SCIENCES
structural codes. We got fire codes
before we got structural codes. Now
we also have structural codes. Guess
what came last? The energy codes.
Not much happens with plumbing
anymore-same goes for plumbing
codes. Same with fire and same with
structure. What I am trying to say is
that plumbing, fire and structural
practice is mature and well established.
Not so with energy. We are
screwing things up, and it is going
to get worse before it gets better. As
we change the energy flow across
buildings, things get very different-
especially when we start looking at
degradation mechanisms-damage
functions.
Water is one of the three principal
damage functions affecting building
materials and assemblies, with the
other two being heat and ultraviolet
radiation. Arguably, water is the
most significant damage function.
If the goal is for buildings to last
a long time, we have to build them
dry, keep them dry and let them
dry if they get wet. Not complicated
in principle. It shouldn't be complicated
in practice, but often is. It
didn't used to be-what changed?
What Has Changed
Three big things have changed in
our lifetimes:
* We don't build out of rocks and
hundred-year-old trees anymore;
* We have very little energy
exchange from the inside to outside
and vice versa; and
* We have heating, cooling and
ventilation systems that condition
the inside almost year-round.
First, the materials that buildings
are constructed from have changed
dramatically. The newer materials
are by and large more sensitive to
28
ASHRAE JOURNAL ashrae.o rg
PHOTO 1 Moisture Sensitive Materials. Oriented
strand board is significantly more moisture sensitive
than plywood.
PHOTO 2 Thermal Insulation. Significant increases
in thermal insulation added to wall assemblies,
roof assemblies and foundation assemblies.
water damage than the older traditional
materials (Photo 1). I am beginning
to view engineered wood as an
insult to wood and to engineers. We
used to go to forests, take big trees
down, cut them into boards, build
boats out of them and sail them
around the world-try doing that with
oriented strand board.
So are we going to go back to rocks
and hundred-year-old trees? Nope.
We have to change the way we build
to accommodate the new realities.
Second, thermal insulation was
added to wall, roof and foundation
assemblies (Photo 2). The function
was to keep the heat inside during
the heating season and keep the heat
outside during the cooling season.
We added more and more and more,
reaching the point where very little
energy exchange happens across
building assemblies.
This is both good and bad. The good
is that buildings are very comfortable
and consume very little energy.
The bad is that the ability of building
assemblies to dry-should they start
out wet or get wet during service-has
been reduced. Drying is an energy
exchange process. Less movement of
energy yields less drying.
When we had poorly insulated
buildings, the energy exchange
was great, and we were not very
J A N U A RY 2023
concerned about " incidental water. "
For example, windows have always
leaked a little. When windows leaked
into uninsulated or poorly insulated
wall assemblies, they were able to
dry due to the exchange of energy
across the wall assembly. We called
this water leakage " incidental water "
and didn't worry much about it as it
did not lead to damage.
Today, we can't ignore " incidental
water " as energy is not available to
promote drying. This " no longer
incidental water " has led to fundamental
changes in how we install
windows and doors, flash service
penetrations and install claddings.
Third, heating has been around for
a long time. Cooling is a more recent
development. Today, except in very
limited circumstances, buildings
are heated and cooled year-round.
Buildings are also now mechanically
ventilated. Buildings no longer
rely on operable windows for an
exchange of air between the interior
and exterior. Again, the good news
is that buildings are much more
comfortable and energy efficient.
With controlled mechanical ventilation,
we can control the quality and
the quantity of the air buildings
exchange with the exterior.
The bad news is that during cooling
periods, interior surfaces are colder
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ASHRAE Journal - January 2023

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