Roxul ComfortBoard IS User Manual
Insulating Sheathing for
Residential Construction
Application Guide for:
ROXUL® COMFORTBOARD™ IS
1 ROXUL® The Better Insulation™
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Prepared by:
167 Lexington Court, Unit 5
Waterloo, Ontario
Canada N2J 4R9
Primary Author:
John Straube, Ph.D., P.Eng.
Illustrations by Building Science Corporation of Somerville, MA unless
otherwise noted.
DISCLAIMER: Building Science Consulting Inc. and Roxul Inc. have exercised due care to insure that the data and information
contained in this document is accurate. However, this document is for general reference use only. Specific end use
applications vary widely as to design, materials, and environments. Thus, what is appropriate in any specific end use application
is a determination that must be made independently by the experienced engineer in their own professional ju dgment. Building
Science Consulting and Roxul fully disclaim any liability for any of the content contained in herein whether such liability be
premised on a theory of contract, tort, or otherwise.
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Contents
INTRODUCTION: WHAT YOU WILL FIND IN THIS GUIDE 2
BUILDING SCIENCE FOR COMFORTBOARD IS WALLS 4
A functional overview of the building enclosure 4
The “Perfect” Wall 5
Rain Penetration Control 6
Drained Screen Approach 6
Selection of Drainage Plane Material 8
Recommendations for rain penetration control 8
Air Control 11
Basic requirements of Air Barrier Systems 12
Thermal Control 13
Thermal bridging 13
Condensation Control 15
Cladding attachment through Continuous Insulation 17
Recommendations for thermal control by climate zone 19
Vapor Control 21
Inward Vapor Drive 21
Recommendations for vapor control by climate zone 23
MATERIAL PROPERTIES 25
INSTALLATION DETAILS 27
01. “Thick ci” Cladding Attachment System 28
02. Foundation-to-Wall Interface 31
03. Floor Slab-to-Wall Interface 33
04. Inside Corner – Horizontal Section 35
05. Outside Corner – Horizontal Section 37
06. Punched Window Interface – Installation Sequence 39
07. Wall-to-Balcony Interface 43
08. Wall-to-Roof Interface 45
REFERENCES AND RESOURCES 47
INSULATING SHEATHING FOR RESIDENTIAL CONSTRUCTION APPLICATION GUIDE
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Introduction: What You Will Find in this Guide
This application guide covers the use of ROXUL
COMFORTBOARDTM IS in residential construction for low- and
mid-rise buildings in continental North American locations.
The use of Insulating Sheathing (IS)—rigid or semi-rigid
insulation board products installed to the exterior of the
building structure—is becoming more common in all parts of
North America with recent changes to energy efficiency
requirements in building codes and standards.
In cold climates the use of exterior insulating sheathing boards
has been a method of increasing the thermal performance of
the enclosure, as well as a means of reducing the condensation
potential with exterior wall assemblies. While insulating
sheathing was initially used on cold climates for these reasons,
the benefits associated with increased thermal performance
make it a viable technology in other climate zones as well.
Modern enclosure design has improved performance of
residential wall assemblies in other ways as well by including an
air barrier system to control movement of air and a drainage
plane to control rain water intrusion. These changes, combined
with now widespread use of light claddings (non-selfsupporting), has created a number of new challenges, including:
Detailing drained screen assemblies to manage water
intrusion in high exposure areas
Maintaining continuity of exterior air barrier systems
through penetrations and interfaces with other
enclosure elements
Providing continuous thermal insulation and
minimizing or eliminating thermal breaks caused by
structure and other enclosure penetrations
Detailing cladding attachment for light- and mid-
weight cladding systems
This guide describes the use of ROXUL® COMFORTBOARDTM IS
to meet these challenges for residential wall assemblies.
Inside, you will find a building science primer with
recommendations by climate zone and a series of best practice
enclosure detail drawings.
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Here are some examples of buildings addressed by this guide.
Detached House
Single unit, light wood frame construction; up to 3 storey’s in
height. Typically one or two family dwelling.
This type of building is typically covered by the IRC
(International Residential Code) building code in the US; and
Part 9 of the NBCC (National Building Code Canada) in
Canada.
Row (Town) House
Single unit, light wood frame construction with one or more
common party walls up to 3 storey’s in height. Typically one
or two family dwelling.
This type of building is typically covered by the IRC
(International Residential Code) building code in the US; and
Part 9 of the NBCC (National Building Code Canada) in
Canada.
MURB – Multi-Unit Residential Building
Multi unit residential building of wood frame construction;
typically in the townhouse style and/or 3-4 storey’s in height.
5-6 storey, wood frame, residential buildings have become
more common in parts of North America.
Buildings of this type over 3 storey’s in height are covered by
the IBC (International Building Code) building code in the US;
Buildings over 3 storey’s in height, or with a building area
over 600m2 are covered by Parts 3,4,5 and 6 of the NBCC
(National Building Code Canada) in Canada.
Wood-Frame Commercial Building
Low-rise wood frame construction; typically used in low rise
commercial and light industrial buildings. Wood-frame
commercial buildings of this type are often built using similar
techniques to building low-rise wood-frame residential
buildings.
Buildings of this type are covered by the IBC (International
Building Code) building code in the US. In Canada buildings of
this type up to 3 storey’s in height and less than 600m2 in
building area, and belonging to Groups C, D, and E are
covered by Part 9 of the NBCC (National Building Code
Canada). Low- and Medium- hazard Group F industrial
buildings are also covered by Part 9 in Canada.
INSULATING SHEATHING FOR RESIDENTIAL CONSTRUCTION APPLICATION GUIDE
Building Science for COMFORTBOARD IS Walls
A functional overview of the building enclosure
The building enclosure is defined as the physical component of a building that separates the interior
environment from the exterior environment: it is an environmental separator. In general, the physical
function of environmental separation can be further grouped into three useful sub-categories as follows:
1. Support, i.e., to support, resist, transfer and otherwise accommodate all structural loading
imposed by the interior and exterior environments, by the enclosure, and by the building itself.
The enclosure, or portions of it, can sometimes be an integral part of the building superstructure
either by design or in actual performance.
2. Control, i.e., to control, block, regulate and/or moderate all the loadings due to the separation
of the interior and exterior environments. This largely means the flow of mass (rain, air, water
vapor, pollutants, etc.) and energy (heat, sound, fire, light, etc.).
3. Finish, i.e., to finish the surfaces at the interface of the enclosure with the interior and exterior
environments. Each of the two interfaces must meet the relevant visual, aesthetic, durability
and other performance requirements.
Control and support functions must continue across every penetration, every interface and every
assembly. The lack of this continuity is the cause of the vast majority of enclosure performance problems.
For physical performance, the most common required enclosure control functions include resistance to:
rain penetration, air flow, heat transfer, condensation, fire & smoke propagation, sound and light
transmission (including view, solar heat, and daylight), insect infestation and particulate penetration, and
human access. As these functions are required everywhere, continuity of these control functions,
especially at penetrations, connections and interfaces between materials, is critical to a successful
enclosure.
The most important control function with respect to durability is rain control followed by air control,
thermal control, and vapor control. The level of fire and sound control required varies with code
requirements and owner requirements. This guide will provide recommendations for residential wall
construction with insulating sheathing for rain control, air control, thermal control, and vapor control.
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Figure 1: The "perfect" wall
The “Perfect” Wall
The support/control/finish components of a typical
enclosure assembly are presented in a conceptually
“perfect” sequence in Figure 1.
The concept diagram shows an exterior finish layer
(the “cladding”) outside of the thermal, air, vapor,
and water control layers, which in turn are to the
exterior of the building structure and interior finishes.
By locating the heat flow control layer (insulation)
on the exterior of the structure and by locating the
combined air, water, and vapor control layers
between the structure and the insulation, the
structure and control layers are protected from UV exposure, impact, and temperature extremes,
thereby increasing the durability of the critical control layers. Such a strategy works well in all climate
zones, from Northern heating-dominated climates to hot and humid Southern climates.
Most residential walls include insulation in the structural cavity – which doesn’t follow the sequence of
layers described above. The typical residential wall is a balance of performance, cost, and constructability
issues.
Residential structures typically use a relatively non-conductive structural frame—the structure is wood
and wood material based. Cavity fill insulation is also typically less expensive and since the space for
insulation is provided by the structural cavity, there is no need for special attachment details. There is a
performance compromise with this approach, however, because the insulation within the structural
cavity lowers the temperature of the exterior sheathing during wintertime conditions, increasing the risk
of condensation. This risk can be managed with the use of insulating sheathing and is described in more
detail in the following sections.
The idea of the perfect wall is intended to guide designers on the proper principles during concept design.
The same approach can be extended for other enclosure elements such as roofs and foundations and
should be used to ensure continuity of the enclosure control layers when designing details describing the
connection between enclosure components such as control joints, window and mechanical penetrations.
The details provided in this guide use this approach.
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Rain Penetration Control
There are three recognized design strategies to control rain penetration within and through the
enclosure: Storage, Drained Screen, or Perfect Barriers.
In a Storage (or Mass) approach, it is assumed that water penetrates the outer surface of the wall and
then is eventually removed by drying to the inside or outside. The maximum quantity of rain that can be
controlled is limited by the storage capacity available relative to drying conditions. Some examples of
mass systems include adobe walls, thatched roofs, solid multi-wythe brick masonry, and single-wythe
block masonry that is still employed for some modern buildings.
Drained enclosures assume some rainwater will penetrate the outer surface (hence the cladding “screens”
the rain) and therefore the assembly must be designed to remove this water by providing drainage
(comprised of a capillary breaking drainage plane, a drainage gap, flashing, and weep hole/drain). Many
cladding systems, such as brick veneer and stucco, leak, as do the joints between other cladding types,
such as shakes, terra-cotta, small metal panels, or natural stone. For these cladding types drainage is a
practical and successful system of rain penetration control.
Perfect Barrier systems stop all water penetration at a single plane. Such perfect control required the
advent of modern materials. Because it is difficult to build and maintain a perfect barrier with many
materials, it is common to recommend the use of drained walls. However, some systems, usually factory
built, provide wall elements that are practical perfect barriers. For example, architectural precast
concrete can be considered watertight, as can glazing, and roof membranes. The joints between perfect
barrier elements should almost always be drained joints in the form of two-stage sealant joints or similar.
Drained Screen Approach
The drained screen approach is considered to be best practice for rain control for residential buildings
using insulating sheathing.
The term “rain screen” is applied to some drained systems, but the term is imprecise, as it means
different things to different people. Drained walls may also be vented (a single, or single line of openings
in the cladding connected to the exterior), ventilated (at least two openings through the cladding usually
distributed between the top and bottom of the cavity), or even pressure-moderated (the air pressure in
vented & ventilated walls tends to follow the exterior wind pressure, thereby “moderating the pressure”).
Rain screen is applied loosely to all three different types of drained walls.
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Figure 2: “Screened” and Drained enclosure walls
As drained systems can accommodate a range of claddings and backup systems, this approach to rain
control has justifiably received a lot of attention from researchers and practitioners.
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Selection of Drainage Plane Material
Drainage planes are water repellent materials (building paper, house wrap, sheet membranes, etc.) that
are located behind the cladding and are designed and constructed to drain water that passes through the
cladding. They are interconnected with flashings, window and door openings, and other penetrations of
the building enclosure to provide drainage of water to the exterior of the building. The materials that
form the drainage plane overlap each other shingle fashion or are sealed so that water drains down and
out of the wall. The drainage plane is also referred to as the “weather resistive barrier” or WRB. A wall
design typically has a single primary drainage plane but may have multiple water-shedding layers as part
of a comprehensive water management strategy.
The most common drainage plane is “tar paper” or building paper. More recently, the terms “housewrap”
or “building wrap” have been introduced to describe building papers that are not asphalt impregnated
felts or coated papers such as polyethylene or polypropylene films. Drainage planes can also be created
by sealing or layering water resistant sheathings such as a coated structural sheathing. Finally, fully
adhered sheet membranes, or trowel and spray applied coatings can act as drainage planes.
Drainage planes can be vapor permeable or vapor impermeable depending on climate, location within
the building enclosure or required control function. Building papers and “housewraps” are typically vapor
permeable (more than 10 perms) whereas fully adhered sheet membranes and trowel applied coatings
are typically impermeable (less than 0.1 perms). There are a few recently developed spray and trowel
applied coatings that are semi-vapor permeable (1 to 10 perms) that are likely to see wider application in
the near future.
Recommendations for rain penetration control
The significance of rainwater management cannot be over-emphasized: along with the structural
support function it is usually this functional requirement that defines an enclosure design approach.
The climate and the site play a large role in defining the rain exposure that a building is exposed to. The
amount of annual rainfall is one factor in gauging the rain exposure for a wall assembly (see Figure 3
below) but this is modified by the coincidence of rainfall with wind events, the orientation of the building,
and height of the building. Most parts of the world experience a significant amount of wind-driven rain,
and those areas exposed to typhoons can have extreme exposure conditions. While this type of climate
demands good rain control strategies for enclosure walls, the rain deposited on walls can be significantly
reduced by good design and siting.
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Figure 3: Annual Rainfall Map
(From Building Science Corporation. Based on
information from the U.S. Department of
Agriculture and Environment Canada)
Drained Screen Wall Recommendations
Screened wall systems are inherently more forgiving than either mass or perfect barrier systems.
Properly designed and built screened wall systems will provide economical and durable rain penetration
control. Failures in screened systems tend to occur because drainage was not provided (either through a
design or construction failure).
The most reliable and widely applicable approach is to follow the mantra:
Proper siting of the building and the use of sloped hip roofs and generous overhangs deflect driving rain,
even for tall buildings. Water on the surface of the wall is shed from and deflected around openings by
surface features, drip edges, and protruding flashing. Water is removed from the base of the wall by
sloping the grade, and siding is kept at least 8” (200 mm) above grade to protect it from splashes.
Rainwater will penetrate the cladding at joints, laps and penetrations. This water should be removed by
drainage through a drainage space and redirected to the exterior by the use of waterproof flashing with
all lap joints sealed.
Water will remain within the drainage cavity, will be absorbed into the cladding, and may even penetrate
into the structural sheathing or stud space. This water should be removed by drying to the exterior and
the interior by allowing diffusion drying and ventilating the space behind the cladding.
“Deflection, Drainage/Exclusion/Storage, and Drying”.
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Window Installation
Perhaps the most common rainwater control failure occurs at window penetrations. Regardless of which
rain penetration control strategy is used, window and door penetrations through a cavity wall should be
drained. Sub-sill flashings (see Figure 4) of various types are widely available for this purpose. For
drained systems, the flashing can drain into the drainage gap.
Figure 4: To ensure resistance to rain penetration, sub-sill flashing below all window and door openings is a
critical requirement.
Figure 4 shows sub-sill flashing for “punched” (i.e., a window unit within a wall) window openings in a
section of wall. Other openings such as large curtain wall sections and patio doors should also be
protected with sub-sill flashing. Step-by-step instructions for integration of the window and drainage
plane are provided in the details section of this guide.
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Air Control
There are three primary classes of reasons why the control of air flow is important to building
performance:
1. Moisture control – water vapor in the air can be deposited within the enclosure by condensation
and cause serious health, durability, and performance problems.
2. Energy savings – air leaking out of a house must be replaced with outdoor air, which requires
energy to condition it. Approximately 30% to 50% of space conditioning energy consumption in
many well-insulated houses is due to air leakage through the building enclosure. Air movement
within the enclosure, either through low-density insulation or in spaces around insulation can
reduce the effectiveness of thermal insulation and thus increase energy transfer across the
enclosure.
3. Comfort and health – cold drafts and the excessively dry wintertime air that results from
excessive air leakage directly affect human comfort, wind-cooled portions of the interior of the
enclosure promote condensation which supports biological growth which in turn affects indoor
air quality, airborne sound transmission control requires good airflow control, and odors and
gases from outside and adjoining buildings often annoy or cause health problems.
There are other circumstances that require the control of air flow; for example, to control smoke and fire
spread through air spaces and building voids and shafts in multi-family residential buildings, but these
are situations that deal with extreme events, not typical service.
The primary plane of air flow control in a wall is generally called the air barrier. Because such a plane is in
practice comprised of elements and joints, the term air barrier system (ABS) is preferred. In framed, lowrise residential buildings, the primary air barrier system is often located on the interior of the exterior wall,
comprised of either an inner layer of drywall (sealed around the perimeter and at all penetrations) or
sealed polyethylene. However, an exterior air barrier system is preferred because fewer penetrations
need to be accommodated and it is more easily inspected. An exterior ABS can be constructed using
outer layers of sheathing (such as gypsum, waferboard, and fiberboard) with tapes or sealed housewrap.
Unsealed housewrap or building paper provides additional resistance to out-of-plane air flow through the
enclosure assembly. In many modern building assemblies, exterior sheathing is designed and detailed to
be part of an outboard air barrier system and additional layers providing resistance to air flow are
provided to the interior. Note that the plane of airtightness labeled by the designer (and all building
sections should indicate what is intended to be the air barrier) or builder as the air barrier system may not
in fact act as the ABS if that plane is not made continuous through all construction details.
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Basic requirements of Air Barrier Systems
Typically, several different materials, joints and assemblies are combined to provide an uninterrupted
plane of primary airflow control. Regardless of how air control is achieved, the following five
requirements must be met by the air barrier system (ABS):
1. Continuity. This is the most important and most difficult requirement. Enclosures are 3-D
systems! ABS continuity must be ensured through doors, windows, penetrations, around
corners, at floor lines, soffits, etc.
2. Strength. If the ABS is, as designed, much less air permeable than the remainder of the
enclosure assembly, then it must also be designed to transfer the full design wind load (e.g., the
1-in-30 year gust) to the structural system. Fastenings can often be critical, especially for flexible
non-adhered membrane systems.
3. Durability. The ABS must continue to perform for its service life. Therefore, the ease of repair
and replacement, the imposed stresses and material resistance to movement, fatigue,
temperature, etc. are all considerations.
4. Stiffness. The stiffness of the ABS (including fastening methods) must reduce or eliminate
deflections to control air movement into the enclosure by pumping (movement of the air barrier
pulls and pushes air into and out of enclosure cavities). The ABS must also be stiff enough that
deformations do not change the air permeance (e.g., by stretching holes around fasteners)
and/or distribute loads through unintentional load paths.
5. Impermeability. Naturally, the ABS must be impermeable to air. Typical recommended air
permeability values are less than about 1.3 x 10-6 m3/m2/Pa. However air barrier materials are
commonly defined as materials which pass less than Q< 0.02 lps/m2 @75 Pa. Although this is an
easy property to measure it is not as important as might be thought. In practice, the ability to
achieve other requirements (especially continuity) are more important to performance, and the
air “permeance” of joints, cracks, and penetrations outweighs the air permeance of the solid
materials that make up most of the area of the ABS. Hence, a component should have an air
leakage rate of less than Q< 0.2 lps/m2 @75 Pa, and the whole building system should leak less
than Q< 2.0 lps/m2 @75 Pa.
Joints, penetrations, and transitions are the critical link in achieving airtightness. At penetrations and
transitions, details must show how an uninterrupted, strong and airtight plane continues from the wall
element to other components of the enclosure such as windows, roof and foundation assemblies, while
accommodating dimensional construction tolerances and in-service movements.
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Thermal Control
As society demands that residential buildings consume less energy and generate less pollution,
minimizing the flow of heat through the enclosure has become an increasingly important function for the
enclosure to perform. The control of heat flow is also important for the control of interior surface
temperatures, and hence ensuring human comfort and avoiding cold weather condensation. Controlling
the temperature of various elements and layers within an enclosure assembly can be used to avoid
condensation or enhance drying, both of which influence durability.
R-value is commonly used to measure the thermal control of insulation products. However, this metric
does not account for the impacts of thermal bridging, air leakage, installation quality, or thermal mass. It
is this multitude of factors that working together delivers good thermal control.
Thermal bridging
Heat flow is often greater at corners, window frames, intersections between different assemblies, etc.
When heat flows at a much higher rate through one part of an assembly than another, the term thermal
bridge is used to reflect the fact that the heat has bypassed the thermal insulation.
Thermal bridges become important when:
they cause cold spots within an assembly that might cause performance (e.g., surface
condensation), durability or comfort problems
they are either large enough or intense enough (highly conductive) that they affect the total
heat loss through the enclosure
Thermal bridging can severely compromise thermal control and comfort in some building types. Heat
flow through steel stud walls is dominated by heat flow through the metal components (see Figure 5).
Figure 5: Best case R-values for walls with no extra framing for windows, floors or partitions.
Failure to break these thermal bridges can reduce the R-value of the insulating components by 50 to 80%.
INSULATING SHEATHING FOR RESIDENTIAL CONSTRUCTION APPLICATION GUIDE
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