Energy-Saving Assemblies
in Commercial Structures
Matthew Brown, CGP, APADisclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the
Softwood Lumber Board.
“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #G516.
Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.
This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.
__________________________________
Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
Course Description
While it’s fairly well known that wood products sequester carbon and tend to
require less energy to manufacture than other building materials, their
performance related to operational energy efficiency is sometimes overlooked.
From a thermal perspective, wood-frame building enclosures are inherently
more efficient than steel-frame, concrete, or masonry construction—because of
the insulating qualities of the wood structural elements, including studs, columns,
beams and floors, and because wood stud walls are easy to insulate. Using real-
world project examples, this presentation will examine options for utilizing wood-
frame assemblies to achieve compliance with the International Energy
Conservation Code.
Learning Outcomes
Identify and understand IECC pathways for
compliance.
Develop a general understanding of wood frame
construction in choosing pathways for compliance.
Recognize the energy advantages of utilizing wood
construction materials.
Understand the means and methods for utilizing
wood construction through demonstration of real-
life compliance scenarios.
History of Energy Codes
A Brief History of Commercial Codes
U-Factor
Total Building
Performance
(software)
R-Value
R-values
C402.1.3
Performance
Alternative
C407
U-factor
C402.1.4
ASHRAE
90.1
ASHRAE
90.1-2013
IECC
OR
Prescriptive
Four Options to Commercial Energy Code Compliance
2015 IECC Climate Zones
Prescriptive –R-Value Method C402.1.3
Climate Zone 4 5 6
All Other Group R All Other Group R All Other Group R
Mass R-9.5ci R-11.4ci R-11.4ci R-13.3ci R-13.3ci R-15.2ci
Metal Building R-13+13ci R-13+13ci R-13+13ci R-13+13ci R-13+13ci R-13+13ci
Metal Framed R-13+7.5ci R-13+7.5ci R-13+7.5ci R-13+7.5ci R-13+7.5ci R-13+7.5ci
Wood Framed R-13+3.8ci
or R-20
R-13+3.8ci
or R-20
R-13+3.8ci or
R-20
R-13+7.5ci
or R-
20+3.8ci
R-
13+7.5.8ci
or R-20+3.8
R-13+7.5ci
or R-
20+3.8ci
Above Grade Walls
Prescriptive –U-Factor Method C402.1.4
Above Grade Walls
Climate Zone 4 5 6
All Other Group R All Other Group R All Other Group R
Mass U-0.104 U-0.090 U-0.090 U-0.080 U-0.080 U-0.071
Metal Building U-0.052 U-0.052 U-0.052 U-0.052 U-0.052 U-0.052
Metal Framed U-0.064 U-0.064 U-0.064 U-0.064 U-0.064 U-0.057
Wood Framed U-0.064 U-0.064 U-0.064 U-0.064 U-0.051 U-0.051
U-Factor Trade-off Approach
Allows limited flexibility
in the building envelope
design.
R-value for R-value
Trade.
Does not credit high
efficiency equipment, air
sealing and duct sealing.
Total Building Performance
Allows greatest flexibility in code.
Credits tight infiltration, ducts and HVAC equipment.
Software usage depends on occupancy type.
Energy Efficiency Analysis of Three Construction Material Types
Multifamily Building Design: Multifamily Group R
3 story on slab
28,500 sq. ft.
27 units, 57 bedrooms
256,500 cu. ft. conditioned air
Philadelphia
Wood and Steel Framed WallsComparison - Composition
R-13 Cavity
Insulation
1-1/2” R-7.5
Continuous
Insulation
Water resistant
barrier or tape
joint
Mesh
Drainage
5-1/2” Steel
header
1/2” Drywall
5-1/2” Studs and
plates
R19 Compressed or
R18 cavity insulation
Wood structural
panel sheathing
Water resistant
barrier
Exterior Cladding
v
Exterior
3-1/2” Steel studs
Wood and Masonry Framed WallsComparison - Composition
5-1/2” Steel
header
R19 Compressed or
R18 cavity insulation
Wood structural
panel sheathing
Water resistant
barrier
Exterior Cladding
Exterior
1/2” Drywall
5-1/2” Studs and
plates
Thermal Characteristics of Wood & Steel
Steel Wall Construction
Exterior Insulation
Wood Wall Construction
Interior GypsumExterior Cladding
Thermal Bridging
Thermal Characteristics of Wood & Masonry
Masonry Wall Construction
Exterior Insulation
Wood Wall Construction
Interior GypsumExterior Cladding
Thermal Bridging
Above Grade Wall Analysis
Wall Assemblies1 Total Energy (MMBTU) Wall – Energy Cost2
CZ 4- Wood R-20 Wall 95.40 $1030.14
CZ 4-Steel R-13 + 7.5 c.i. 94.20 $1019.70
CZ 4-Block +11.4 c.i. 90.00 $980.33
1. Continuous Insulation (c.i.)
2. Monthly total energy usage and cost for Above Grade Wall assemblies only.
Above Grade Wall Analysis
Assembly1 Total Energy (MMBTU) ABG wall – Energy Cost2
CZ 5 - Wood R-21 - no c.i 92.2 $594.00
CZ 5 - Wood R-20 + 3.8 c.i. 98.6 $632.00
CZ 5 - Steel R-13 + 7.5 c.i. 94.1 $605.00
CZ 5 - Masonry + R-13.3 c.i. 108.7 $709.00
CZ 6-Wood R-21Wall- no c.i 112.7 $827.86
CZ 6-Wood R-20+3.8 c.i. 110.40 $825.82
CZ 6-Steel R-13 +7.5 c.i. 125.10 $923.43
CZ 6-Block + R-15.2 c.i. 141.00 $1034.70
1. Continuous Insulation (c.i)
2. Monthly total energy usage and cost for Above Grade Wall assemblies only.
Results
Code requires steel and masonry to have continuous
insulation while wood does not in order to meet
assembly U-factor levels.
Studies have shown that wood buildings can cost
significantly less to construct while providing the
same or better energy performance.
A common misconception is that continuous
insulation makes masonry and streel walls more
energy efficient than wood walls without continuous
insulation.
The effects of thermal bridging in wood walls is often
overstated.
Commercial Roof Insulation Requirements
Roof/Ceiling Assemblies –R-Values
Climate Zone 4 5 6
All Other Group R All Other Group R All Other Group R
Insulation Above deck R-30ci R-30ci R-30ci R-30ci R-30ci R-30ci
Wood Framed R-38 R-38 R-38 R-49 R-49 R-49
Table C402.2 – Opaque Thermal Envelope Requirements.
Roof/Ceiling Assemblies –U-Factor
Climate Zone 4 5 6
All Other Group R All Other Group R All Other Group R
Insulation Above
deck
U-0.032 U-0.032 U-0.032 U-0.032 U-0.032 U-0.032
Wood Framed U-0.027 U-0.027 U-0.027 U-0.021 U-0.021 U-0.021
Table C402.3 – Opaque Thermal Envelope Requirements.
Energy Efficiency Analysis of Roof/Ceiling Assemblies
Building Design: Multifamily Group R
3 story on slab
28,500 sq. ft.
27 units, 57 bedrooms
256,500 cu. ft. conditioned air
Philadelphia
Insulation Entirely above the Roof Deck
Foam board insulation -considered continuous
Insulation (c.i.)
Varies in thickness
R-values range from R-5 to R-6 per inch
Wood Attic
Install insulation between
framing members
Roof/Ceiling Analysis
Roof Assemblies Total Energy
(MMBTU)
Energy Cost2
CZ 4- R-30 Above Deck 30.70 $225.45
CZ 4- R-38 Wood Attic 21.50 $158.27
1. Continuous Insulation (c.i.)
2. Monthly total energy usage and cost for Roof/Ceiling assemblies only.
Roof/Ceiling Analysis
Assembly1 Total Energy (MMBTU) ABG wall – Energy Cost2
CZ 5-R-30 Above Deck 39.00 $282.98
CZ 5-R-49 Wood Attic 21.50 $156.65
CZ 6 - R-30 Above Deck 43.1 $317.42
CZ 6- Wood Attic R-49 26.8 $196.56
1. Continuous Insulation (c.i)
2. Monthly total energy usage and cost for Roof/Ceiling assemblies only.
Raised Heel Trusses
Insulation:
Energy-heel truss
Full-height insulation extends
over top plates
Continuous wood wall sheathing
overlaps onto truss heel
Raised Heel Roof/Ceiling Analysis
Roof Assemblies Total Energy
(MMBTU)
Energy Cost2
CZ 4 - Above deck R-30 c.i.1 53.3 $338.00
CZ 4 - Wood attic R-38 31.5 $203.00
CZ 4 - Wood attic raised heel3 R-30 30.3 $195.00
Note: Raised Heel Trusses with R-30 insulated yield a 3.2% energy savings on average.
1. Continuous Insulation (c.i.)
2. Monthly total energy usage and cost for Roof/Ceiling assemblies only.
3. Raised Heel Truss
Raised Heel Roof/Ceiling Analysis
Assembly Total Energy
(MMBTU)
Above Grade wall –
Energy Cost2
CZ 5- Above Deck R-30 c.i 30.10 $205.36
CZ 5- Wood Attic R-49 26.8 $196.56
CZ 5 Wood Attic Raised Heel3 R-38 25.1 $184.09
CZ 6- Above Deck R-35 c.i 45.5 $333.27
CZ 6- Wood Attic R-49 34.6 $253.87
CZ 6-Wood Attic Raised Heel3 R-38 33.22 $243.74
Note: Raised Heel Trusses with R-38 insulated yielded a 4% on average
savings in energy.
1. Continuous Insulation (c.i)
2. Monthly total energy usage and cost for Roof/Ceiling assemblies only.
3. Raised Heel Truss
Results
Wood attic assemblies are more energy efficient than
insulation above deck assemblies.
Studies have shown that wood roof assemblies can
cost significantly less to construct.
In many cases the energy cost of the wood attic was
half that of the metal framed buildings with
continuous insulation roofs.
Wood raised heel trusses require less insulation
while providing better energy performance.
Performance Code Compliance
Simulated Performance Alternative
Performance Based Code Compliance
R-13+ 3.8 c.i. Exterior walls
(U-0.062)
R-38 Attic insulation
U-.32 Windows
R-10 Footing insulation -
24 inches deep.
IECC Reference Building: Proposed Design:
R-19 Exterior walls, no c.i.
(U-0.064)
R-30 Attic insulation with
raised heel trusses
U-.32 Windows
R-10 Footing insulation -
36 inches deep.
Whole Building Energy Performance
Climate Zone Above Grade Walls1 Attic/Roof Footings Energy Cost2
CZ 4 Wood R-19 - no c.i. R-30 Raised Heel3 R-10, 36 inches vertical $4,178.00
CZ 4 Wood R-13 + 3.8 c.i. R-38 Attic R-10, 24 inches vertical $4,204.00
CZ 4 Steel R-13 + 7.5 c.i. R-20 c.i.1 R-10, 24 inches vertical $4,658.00
CZ 4 Masonry + R-13.3 c.i. R-38 Attic R-10, 24 inches vertical $4,912.00
1. Continuous Insulation (c.i.)
2. Yearly energy cost for heating and cooling used to determine 2015 IECC compliance.
3. Raised Heel Truss
Performance Based Compliance
The proposed design
not only meets the 2015
IECC requirements, the
design exceeds them.
By 2.4%
Energy Efficiency Analysis of Three Construction Material Types
Building 2: Elementary School
1 story on slab
50,000 sq. ft.
500,200 cu. ft. conditioned air
Climate Zones 5 and 6
This evaluation was conducted by Nexant Energy Consultants, Boulder, Colorado.
Elementary School Analysis
Wall Assemblies Roof Assemblies Attics Annual Energy Cost
CZ 4 - Wood R-20 R-38 $31,525
CZ 4 - Steel R-13 + 7.5 c.i.1 R-38 $31,269
CZ 4 - Masonry 11.4 c.i.1 R-38 $31,242
1. Continuous Insulation (c.i.)
Attic Roof Assemblies
Wood Attic on Masonry Walls
Wood Attic on Wood Walls
Wood Attic on Steel walls
Elementary School Analysis
Wall Assemblies
Roof Assemblies
Insulation Above Deck1 Annual Energy Cost
CZ 5 - Wood R-20 R-30 c.i $32,675
CZ 5 - Steel R-13 + 7.5 c.i.1 R-30 c.i $32,401
CZ 5 - Masonry 11.4 c.i.1 R-30 c.i $32,373
1. Continuous Insulation (c.i.)
Nexant Analysis Results
Similar to the multifamily analysis code required
assemblies with continuous insulation are not as
energy efficient as wood framed assemblies without
the use of continuous insulation.
Wood framed attics with ceiling insulation are more
energy efficient than assemblies with continuous
insulation over the structural roof systems.
Air leakage Control
According to the US
Department of Energy
as much as 30
percent of a buildings
energy usage can be
from air leakage.
Utility penetrations.
Drop ceilings/utility chases adjacent to the thermal boundary.
Common walls between dwelling units.
Multifamily Building Air Leakage
Key Areas for Air leakage:
Utility Penetration Air Sealing
Drop Ceiling Utility Chase Air Sealing
Common Wall Air Sealing
Air Leakage Testing
Air leakage testing
ensures the air barriers
and air sealing are
functioning.
Energy codes allow
greater trade-offs for
less air leakage.
Principals of Air Sealing
Air is lazy and will take the least path of resistance, start
with the biggest penetrations and gaps and work down to
the smaller ones.
Where air moves so does heat and moisture.
There is not a “one size fits all” solution, balancing
product price, functionality and use is important.
Air sealing is often the most cost effective energy
improvement made to buildings.
On Your Next Project
Code required wood framed assemblies are more cost
effective than other assemblies.
Wood assemblies are more energy efficient that masonry
and steel assemblies.
Both of these points mean lower building costs and
operational energy costs for the client for years to come.
Learning Outcomes
Identify and understand IECC pathways for
compliance.
Develop a general understanding of wood frame
construction in choosing a pathways for compliance.
Recognize the energy advantages of utilizing wood
framed construction materials.
Understand the means and methods for utilizing
wood construction through demonstration of real-life
compliance scenarios.