ASHRAE Journal - August 2014 - 39

Column Building ScienceS

1×4 Wood Furring Attached Through
Rigid Insulation to 2×4 Wood Furring
2×4 Wood Furring Mechanically
Attached to Masonry Wall
Fluid-Applied Water Control
Layer And Air Control Layer

Cladding
Joints Offset Horizontally and
Vertically With Each Layer Taped
Masonry Wall

Interior Plaster and Lath
Figure 1 Perfect Wall Retrofit. Coat the exterior of the masonry with a fluid-applied water control layer and air
control layer. Install rather robust wood furring (2×4s "on the flat") directly to the masonry. Then, insulate over
the entire assembly with rigid insulation and install additional furring for cladding attachment. Finish the entire
thing off with new cladding.

Photo 3 "Secret" Trick. 2×4 wood furring "on the
flat"; once you attach that everything else attaches
to that and it is easy sailing. And it is not a big deal
to attach wood furring directly to masonry or to
concrete; we know how to do that.

preservationists argue for the inside.
2 in. Semi-Rigid Mineral Fiber Insulation;
Fiber Cement Panel
Seams Offset Horizontally and Vertically
But not all uninsulated Chicago
2×4 Wood Furring Mechanically
"Reveal" in Panel Joint
masonry buildings are historic. And
Attached to Masonry Wall
some of them are downright ugly.
Space/Joint Backer
Fluid-Applied Water Control
Layer and Air Control Layer
Many could do with an "insulated
1.5 in. Semi-Rigid
Mineral Fiber Insulation
face lift"-a deep retrofit from the
Metal Hat
outside-a Chicago deep-dish retroMasonry Wall
Channel
fit. So that is where we are going to
go. We already did the inside insulation thing way back when ("Thick As
A Brick," ASHRAE Journal, May 2010).
These buildings can come "jumbo"
Interior Plaster and Lath
sized (Photo 1) or "house" sized (Photo
2). Regardless of size they can be
Figure 2 Non-combustible Perfect Wall Retrofit. If you want to go "all out" use mineral fiber insulation and
metal hat channels. Fluffy rocks covered with cement board held in place with steel anchors and metal channels
addressed the same way. Coat the
installed over a masonry wall will please even the most persnickety Chicago fireman.
exterior of the masonry with a fluidapplied water control layer and air
is Chicago. Fire is a big deal. What complicates things
control layer. Install rather robust wood furring (2×4s "on
even more is that sometimes the buildings are very close
the flat") directly to the masonry. Then insulate over the
entire assembly with rigid insulation and install additional together. Getting a "rated" wall is not easy. No one has
furring for cladding attachment. Finish the entire thing off "burned" these types of configurations. You are going to
have to throw yourself at the mercy of "the authority havwith new cladding (Figure 1). Easy. We can retrofit an unining jurisdiction." Relax. Not all "authorities" are crazy.
sulated masonry wall "with good bones"-and Presto!-get
In fact, most are darn right helpful. But it does help if an
"a perfect wall" out of the deal.
The "secret" trick is the 2×4 wood furring "on the flat"- alderman gives them a call, especially in Chicago.
We got real help from everyone on this issue-manufaconce you attach that, everything else attaches to that and
turers included. All of the walls passed the "don't burn"
it is easy sailing. And it is not a big deal to attach wood
furring directly to masonry or to concrete; we know how "smell test." The rigid foams all have a flame-spread index
of 25 or less and a smoke-developed index of 450 or less
to do that (Photo 3).
What can be easier? Not so fast. Some rigid insulations
Joseph W. Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation in Westford,
Mass. Visit www.buildingscience.com.
burn. Some do not, but are not so rigid. Remember, this
Au g ust 2014

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