Page 52 - Green Builder Nov-Dec 2021 Issue

BY SAM RASHKIN

This is Sam Rashkin’s third in a series of articles based on his
second book, “Housing 2.0: A Disruption Survival Guide.” The
book is intended as a roadmap for high-performance builders to
become the most successful in the industry.

ONSTRUCTION ASSEMBLIES with fibrous
insulation (such as fiberglass, rock wool, or
cellulose) need a complete air barrier on all six
sides. This ensures the thermal control layer
works effectively, since air can flow through
it. Think of the difference outdoors on a cold
windy day with a sweater and jacket made of a
water repellent fabric: Without the jacket, the
cold wind easily passes through the sweater and
C mitigates its thermal resistance.
In contrast, with the jacket functioning as an air impervious
control layer, air flow through the sweater is blocked, resulting
in much more effective thermal protection. It’s the same with
buildings. Note that some types of insulation are air impervious
(e.g., closed cell foam, foil faced rigid insulation) and can function
as the air and thermal control layers.
Exterior weather resistance barrier (think house wrap,
building paper, liquid membrane, and roofing felts) is often
mistaken as the primary air barrier on the exterior of homes.
Yes, such barriers do resist air flow, but this function is already
provided by traditional exterior sheathing materials (e.g., ori-
ented strand board [OSB], plywood, rigid insulation boards).
To ensure a complete air control layer, sheathing needs to be
sealed at all joints, gaps where sheathing is attached to fram-
The marily functions as the water control layer for shedding bulk
ing, and penetrations. Thus, the weather resistant barrier pri-
moisture that gets past the cladding or roofing. And water
gets past all claddings and roofing. They also need to provide
Missing Air adequate vapor flow for wall and roof assemblies to dry to the
outdoors.
On the interior, the primary air barrier is the drywall. The
joints are filled with spackle and taped to form a complete air

Barrier 20 F
o

From OSB to drywall, there’s a 45 F 20 F
o
o
heavy-duty path to insulated Air Barrier Missing
performance. 70 F
o

Figure 1: Air barrier missing at dropped ceiling

50 GREEN BUILDER November/December 2021 www.greenbuildermedia.com