Resources for the Resourceful: Learning about the Building Envelope

If you have been in the HVAC business long enough, at some
point, it occur es to you that the building envelope is an integral
part of a building’s HVAC system; it’s the boundary between the
environment you are trying to control and the uncontrolled
environment. Right after that, you notice that in the typical
building construction you are seeing, there are a lot of potential
breeches of the envelop as illustrated in the pictures
below. 

  

That insight causes you to start looking more closely at the
details construction associated with the buildings you are working
on, be they commercial office buildings, factories, or
houses.  And, in doing that, you begin to realize a few
things; things that at to this point, you had taken for granted or
not even considered.

Insulating the walls with R-19
insulation
does not mean the wall represents a
homogeneous R-19 surface. 

A building that is water tight may not
be air tight and may leak significant amounts of air.

Moisture in the form of water vapor
can enter a building along with the air that leaks in.

About a month or two after that (as you have probably
realized by now, this is my process), you return to a site where
you had been observing the details of the curtain wall construction
with a few questions you want to check out and discover that all of
the things you wanted to look at are now behind drywall and other
finishes and realize: 

Monitoring the integrity of the envelope
as the building ages
will be difficult to impossible
to accomplish via direct observation.

A building that seems to be water
tight
because there is no water running through the
roof or walls may actually be experiencing minor leakage that is
trapped in hidden construction

The now concealed thermal
bridges
created by structural elements could condense
moisture out of air that is leaking into the building and flowing
past them.

Even though these observations seem obvious in
hindsight, for me at least, they were not immediately obvious.
Granted, I understood how envelope construction could impact the
loads my systems would handle.  After all, one of the first
steps in a load calculation was to calculate the heat transfer
coefficients for the roofs, walls and windows that made up the
building I was working on. But, what I didn’t really get for a
while was how important the details of  envelope construction
were to the satisfactory performance of the systems I was so
focused on designing and installing and ultimately, on the
comfortable safe environment they were supposed to deliver. And as
my awareness of the importance of the integrity of the envelope
grew, so did my interest and appreciation of the details behind
envelope design and fabrication.

Information regarding this topic is not as easy to
come by as you might think, especially information regarding the
real world interactions between the indoor environment, the outdoor
environment, and the envelope. So, I was really pleased and excited
when I discovered that Dr. Joseph Lstiburek was a frequent
contributor to the ASHRAE Journal
Building Science column
. Dr. Lstiburek is an expert in the
areas of rain penetration, air and vapor barriers, air quality and
building construction technology in general and specializes in
moisture damage and mold and microbial contamination in buildings.
He has an unusual, engaging and entertaining way of presenting
information that make his columns and presentations a bit different
from all the rest. For instance, in his recent Building Science
column on wine cellars (illustrated below), you will learn about
wine, wine making, psychrometrics and how they all come together if
you happen to be designing a wine cellar. And, with physics being
physics, the lessons apply across the boards.

In addition to the information published in various
ASHRAE documents, his
company’s web site
contains a lot of useful information on
envelope related issues. You can even subscribe to a
monthly newsletter
that will keep you in touch with a field
perspective on building envelope issues that is grounded in
physics.

So, bottom line, take a few minutes to check out the
details of the envelope on your current project and supplement you
investigation with some on line learning using resources like the
ASHRAE and Building Science web sites. It will make you a better
HVAC professional and that is good for all of us as well as the
planet. If you’re curious about my journey down this path, a lot of
it can be found in a paper I published with some folks from
PECI titled Commissioning
and Envelope Leakage: Using HVAC Operating Strategies to Meet
Design and Construction Challenges
which can be found in
the library on the California
Commissioning Collaboratives web site
.

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