This article is from Rick Terry, Quality
Assurance Designee at Building Performance Contractor’s Association
As an industry, we have made great strides in meeting some
of the demands that various energy programs and codes have required relative to
materials and processes; however, as a HERS and green rater that works with
both manufacturers and builders, I see a constant struggle to accept certain
important concepts that enable them to meet requirements.
One of the big ones is the concept of a separate air barrier and thermal
barrier that must remain in contact with each other and work together to
maximize performance. Air barriers are any materials that prevents air from
moving in and out of the building and can be OSB sheeting, rigid foam,
housewrap, caulking, approved tapes, etc… they may or may not have additional
thermal properties; fiberglass batt insulation is not an air barrier. The
responsibility to install and keep intact both the air and thermal barriers are
the manufacturer’s and their builders’.
Thermal barriers are materials that
have higher thermal resistance; i.e. the ability to minimize or even eliminate
the movement of heat through a material or materials.
The plant needs to adhere to the manufacturer’s installation instructions of
the type of insulation being installed in the home. For the majority of homes,
this will be fiberglass batts although we are starting to see more options such
as spray foam applications, and blown in products like cellulose and
fiberglass; but for now, we will focus on fiberglass batts. The standard is
simple: Insulation must make contact with all six sides of a cavity without
compression and gaps. In the case of ceiling insulation with an open attic, it
would be 5 sides.
In addition, the following are key aspects of making that happen:
-
Paper facing on insulation should be against the conditioned side of the
cavity for most of the mid-Atlantic and northern climates of the US. (More
southern, humid climates will reverse this.) -
Cut batts to proper length and width. Fit should be adequate to fill cavity
completely; too long or wide and you can create areas where the insulation
pulls away from the wall; too short and you get gaps top, bottom and/or sides
allowing spaces for air to move. -
For exterior walls with blocking materials, bracing, electrical boxes and
plumbing, insulation needs to cut, scored, and fit so that contact is made
against all surfaces. (This can also be accomplished with a combination of
rigid foam in between the blocking and fiberglass batt w/o facing, over top.) -
For horizontal obstructions like electrical wires, the batt should be split
to go around the obstructions and still contact all surfaces plus fully fill
the cavity. -
DO NOT POKE INSULATION INTO PLACE WITH A STICK! This is one of the most
common practices we see even in plants that have been doing it right for years,
as soon as there is a personnel change, they seem to go back to the stick. It
creates compression areas and/or voids in the insulation that have potential
for future problems like air and moisture movement in the walls.
These key aspects take time…more time than most manufacturers and builders want
to commit but it needs to become a priority as codes and programs require
higher standards. These standards are typically verified through performance
tests like the blower door leakage test, duct leakage test and infrared
imaging. Use your HERS/Green raters to develop a standard and/or checklist for
greater performance and to review best practices with your team.
Rick will have his article on AIR BARRIERS coming soon.
