ICF WALL BUILDING ENVELOPE
Refer to the notes below for details. Note that the current code does not require a rainscreen with ICF
construction. Read our considerations below.
Section 220.127.116.11 of the Canadian Code states that The MAXIMUM allowable vapor permeance of a wall
assembly in Canada is 60 ng.Pa.s.m2 (nanograms per Pascal second meter squared).
Intertek Testing Services verified that the calculated vapor permeance of 2 5/8” (63.5 mm) thickness of
NUDURA® EPS foam panel on the interior side of the concrete wall assembly achieved a MAXIMUM Vapour
Permeance of 36 ng/Pa.s.m2 which is 38% better than the MAXIMUM allowable. Source: Intertek REPORT.
Air Barrier Systems
"The Nudura ICF wall system provides a triple air barrier. The poured in place concrete does not have
joints and qualifies as an air barrier. The rigid insulation on each side also acts as an air barrier."
Source: CTL Group's report.
Air blower tests confirm that air leakage is minimal with ICF walls and concrete.
Rain Penetration Control Strategy
The "Building Envelope Guide for Houses, Second Edition" discusses Rain Penetration Control Strategies
for Wall Systems (page 7). It lists two strategies relevant to ICFs: Mass walls and Rainscreened
- MASS WALLS: "Mass walls are generally cast or poured-in-place concrete, insulated concrete form
(ICF) or masonry. A mass wall can be exposed to precipitation above grade without cladding or
surface finish where it is not subject to deterioration from forces such as mechanical impact or
ultraviolet radiation. ICF walls require cladding for such protection , but do not require a capillary or sheathing membrane between the cladding and the mass wall.
Mass walls are defined by their ability to be exposed to precipitation for a significant period
before moisture penetrate from the exterior to the interior. As long as this type of wall remains without holes or cracks,
and does not allow sufficient water to absorb and migrate through its thickness, it will serve all
of the required functions of protection from precipitation."
- As cracks are induced throughout the ICF wall by the large plastic ties, it is our opinion that the
ICF wall does not qualify as a mass wall. Furthermore, wind driven rain that gets behind the
cladding will enter the cracks in the EPS panels and could enter the cracks in the concrete.
Therefore it is prudent to install a rainscreen.
- RAINSCREEN (page 9): "A rainscreen wall consists of a cladding, a clear air space behind the
cladding sufficiently deep to prevent capillarity (10 mm), and a sheathing membrane (building paper,
house wrap or Vaproshield)." It is our opinion that the installation of a rainscreen is a prudent
option even though it is not required under the "Building Envelope Guide for Houses, Second
Self-Adhered: a fully self-adhered weather resistive and air barrier sheet membrane, fully bonds
to EPS, does not require the use of primers, emits no VOC's, and does not require special equipment