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What is Insulating Sheathing?
Insulating sheathings are sheet/board products (common sizes 2x8,
4x8, 4x9) that are attached to the exterior framing before installing
siding or other exterior covering. Extruded polystyrene (XPS) sheathings
are designed to add insulating value to wall systems and are used
in conjunction with code compliant wall bracing. (See Section R602.10
of the 2003 International Residential Code.)
When Can I Use XPS Insulating Sheathing?
XPS sheathings can be used to cover the entire exterior wall area,
when used in conjunction with code compliant bracing.
What Are The Benefits of Using XPS Insulating
Sheathing?
Although non-insulating wood sheathings, such as plywood and oriented
strand board (OSB), are one option to provide structural integrity
to wall systems, they offer little thermal resistance (with an R-value
of only R-0.6). XPS insulating sheathings, which have an R-value
of R-2 to R-7.5, offer the following added benefits:
- Energy savings
- Improved comfort
- Ease of installation
- Reduced potential for condensation within walls
- Lower cost than non-insulating wood sheathings
Using XPS insulating sheathing in wall systems increases
the value of any home by reducing
operating costs (lower energy bills). Insulating sheathings
like XPS not only add significant R-value to wall systems, they
also reduce air leakage. When air leaks into a home through the
exterior walls, it reduces the efficiency of the insulation in
the wall cavity. You can increase the comfort of your home, while
reducing heating and cooling costs by up to 30% by investing just
a few hundred dollars in proper insulation and weatherization products.
What Types of Residential Wall Systems Incorporate
XPS Insulating Sheathings?
In residential construction, there are a variety of wall systems
that incorporate XPS insulating sheathing. The following are examples
of wall systems that are commonly used in new homes:
Conventional Framed Construction With Wood/Vinyl/Aluminum
Siding
XPS insulating sheathing is attached to exterior framing members
prior to installing the siding. XPS, which is typically used in
conjunction with building code compliant bracing, covers the entire
wall surface, including the attic gable end walls. Building codes
require that foam insulation on attic walls be covered unless specifically
recognized for exposed applications. Consult the XPS manufacturer’s
building code evaluation report for guidance.
Exterior Insulation Finish System (EIFS, Synthetic Stucco)
XPS insulating sheathing is attached to exterior framing prior to
installing the exterior finish. XPS, which is typically used in
conjunction with building code compliant bracing, covers the entire
wall surface, including the attic gable end walls. A stucco lath
(wire or fiberglass mesh) is installed over the foam and is secured
to the underlying framing. A base coat is applied over the lath
and is followed by a finish coat. It is important to consult the
EIFS manufacturer’s installation instructions, since installation
details vary.
Conventional One-Coat Stucco System
XPS insulating sheathing is attached to exterior framing prior to
installing the exterior finish. XPS, which is typically used in
conjunction with building code compliant bracing, covers the entire
wall surface, including the attic gable end walls. The surface of
the insulating sheathing is prepared to accept the stucco covering
by using a wire brush to make the surface rough. A stucco metal
lath is installed over the foam and is secured to the underlying
framing. The cementitious exterior covering (stucco) is applied
directly over the lath. It is important to consult the stucco manufacturer’s
installation instructions, since installation details vary.
Exterior Brick Veneer
XPS insulating sheathing is attached to exterior framing prior to
installing the brick. XPS, which is typically used in conjunction
with building code compliant bracing, covers the entire wall surface,
including the attic gable end walls. Brick ties are installed through
the foam sheathing into the underlying framing. The brick is then
installed with a nominal one-inch air space between the back side
of the brick and the surface of the foam. For further information,
contact the Brick Industry Association.
Insulating Concrete Form System (ICF)
Insulating concrete forms are hollow blocks, panels or planks made
of XPS that are erected and filled with concrete to form the structure
and insulation of exterior walls. These types of permanent modular
formwork units have been used successfully in Europe for over 25
years and have been used in the United States and Canada for approximately
20 years. Homes built using insulating concrete form systems look
like any other home. Stucco, wood siding, and other traditional
exterior finishes can easily be used with these systems. Interiors
are usually dry-walled. In addition, the forms readily accommodate
plumbing and wiring.
The reinforced concrete wall system may be used
as load bearing exterior walls, foundation walls, retaining walls,
and lintels. All ICFs work on the same principle (filling foam forms
with concrete), but differ in size of the form units (blocks, panels
or planks) and unit connections, the shape of the cavities into
which the concrete is poured, and whether the surfaces can accept
the attachment of nails or screws.
For more information on insulating concrete form
systems, go to www.forms.org
or www.concretehomes.org.
Steel Framing
Steel frame construction has historically been used primarily in
commercial construction applications. However, due to the increasing
cost of lumber it is now becoming more common in residential construction.
Cold-formed steel is light-weight, easy to handle, cost effective
and is a high quality alternative to traditional wood framing materials.
There are many advantages to steel framing in residential
walls. However, steel will conduct heat and can influence the effectiveness
of a wall system by allowing non-uniform heat transfer. For this
reason, the American Iron and Steel Institute (AISI, www.steel.org)
published the “Thermal Design Guide for Exterior Walls”
(Publication RG-9405), which is intended to provide designers and
contractors with guidance on thermal design of buildings that utilize
cold-formed steel framing members.
The American Society of Heating, Refrigerating and
Air Conditioning Engineers (ASHRAE)
published a standard, ASHRAE 90.1, that applies an R-value correction
factor for walls with steel framing members. The correction considers
the heat loss through the steel framing and is based on the R-value
of the insulation used in the studs. The International Code Council
(ICC) has adopted the ASHRAE
recommended values for wall sections with steel stud correction
factors and provides alternatives for equivalent steel-framed wall
cavity and rigid foam sheathing R-values (see the International
Energy Code, IECC Table 502.2.1.1.1).
Extruded polystyrene insulation board (XPS) not
only meets the IECC recommendations for exterior insulating sheathing,
it also offers the following important benefits to steel-framed
wall systems:
- Proven thermal performance (R-value) prevents
thermal loss through steel framing members.
- Superior moisture resistance ensures long-term
insulating value in wet environments, such as behind exterior
brick veneer.
- Decreased condensation potential (due to higher
R-value) protects the wall system integrity.
- Outstanding dimensional stability and strength
provides excellent durability.
- Lightweight product allows easy handling and
installation.
Structural Insulated Panel Systems (SIPS)
A structural insulated panel (SIP) is a composite panel consisting
of a thick rigid foam core, such as extruded polystyrene insulation
board (XPS) sandwiched between layers of oriented strand board (OSB)
to create a high R-value structural panel. These composite panels
combine the high R-value of XPS with the strength of structural
wood sheathing to create a panel system that offers more R-value
than conventional 2x4 or 2x6 wood framed walls that have fiberglass
cavity insulation. SIPs are commonly used to construct the floors,
walls, and roofs of houses and buildings.
When a home is built with SIPs, the panels are pre-fabricated
to specifications in a factory, where door and window openings can
be pre-cut. SIPs can also be made in various thicknesses and sizes
to accommodate custom specifications. Once the panels are fabricated,
they are then shipped to the job site where they are quickly joined
together using inset splines. The pre-cutting allows for fast, easy
connections at the job site and, since the panels are prefabricated
and are installed quickly, the potential for exposure to moisture
during construction is greatly reduced.
SIPs are an energy efficient, cost competitive alternative
to conventional stick-built construction and offer several advantages.
For example, SIPs do not contain studs, so no heat is lost at uninsulated
stud locations. Did you know that approximately 25% of the wall
area for a typical wood-framed construction consists of framing
members, which conduct heat, resulting in significant heat loss
unless covered with an insulating sheathing like XPS?
SIPs were first introduced in the 1950’s and
have grown in popularity as a result of the benefits and competitive
cost versus traditional stick-built homes. Click here
for more information on SIPs.
Manufactured Homes
A manufactured home is a single-family house constructed entirely
in a controlled factory environment. These homes are built to the
federal Manufactured Home Construction Standard (HUD Code), which
is administered by the U.S. Department of Housing and Urban Development
(HUD). Manufactured homes may be either single or multi-section
units that are transported to the site on a permanent chassis with
wheels and installed. On-site additions, such as garages, decks
and porches are often added once the house has been installed.
Manufactured homes are constructed similar to traditional
stick-built homes that have insulating sheathing, such as extruded
polystyrene insulation board (XPS), on exterior walls to enhance
the overall thermal performance of the wall system. All building
materials used to construct manufactured homes are purchased in
volume for additional savings. This cost savings is passed along
to the buyer, who can now purchase an affordable home.
For more information on manufactured homes, go to
www.manufacturedhousing.org.
Modular Home
A modular home is a single-family house constructed entirely in
a controlled factory environment. These homes are built to the local
building code where the home will be located. Modular homes may
be either single or multi-section units that are transported to
the site on a permanent chassis with wheels and installed. On-site
additions, such as garages, decks and porches are often added once
the house has been installed.
Modular homes are constructed similar to traditional
stick-built homes that have insulating sheathing, such as extruded
polystyrene insulation board (XPS), on exterior walls to enhance
the overall thermal performance of the wall system. Building materials
used for construction of modular homes tend to be purchased in volume.
Therefore, a home-buyer may be able to more easily purchase an affordable
home.
For more information on modular homes, go to www.modularhousing.com.
Re-siding/Retrofit Applications
The best time to improve your home’s energy efficiency is
when you are replacing worn siding with new siding. In older homes
that have little or no insulation or in homes that have drafts,
one of the best ways to save energy is to add XPS insulating sheathing
or fanfold siding underlayments beneath the new siding. Not only
will this reduce your energy bills, it will also improve your comfort
level.
If you are removing your old siding, you will have
easy access to the original sheathing layer and usually it is possible
to install a layer of insulating sheathing on top of the original
sheathing before installing the new siding. If you do not want to
remove the existing siding, you could install XPS fanfold siding
underlayment or XPS insulating sheathing directly over the top of
the old siding prior to installing the new siding. You may need
to modify the jambs, sills, flashings, etc. depending upon the thickness
of the foam installed.
Your energy savings will depend on several factors.
Every house is different, and your savings will depend on the condition
of your house and the retrofit option that you choose. The Department
of Energy recently sponsored the development of the “Retrofit
Best Practices Guide”, which is now available on the Oak
Ridge National Laboratory website. This guide describes estimated
energy savings for three different retrofitted houses in ten different
cities. The energy savings were estimated using a combination of
experimental measurements and home energy modeling.
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