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Presentation Outline: - Gravity support systems - Design criteria and thermal performance requirements - Canadian energy codes - Nominal vs. Effective R-Values - Thermal modeling and effective - R-values - Conclusions
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June 3, 2013 – 12th Canadian Masonry Conference – Vancouver, BC
Masonry Veneer Support Details: Thermal Bridging
! Mike Wilson, MEng, P.Eng Graham Finch, MASc, P.Eng James Higgins, Dipl.T RDH Building Engineering Ltd. Vancouver, BC
Presentation Outline
! Gravity support systems
! Design criteria and thermal performance requirements
! Canadian energy codes
! Nominal vs. Effective R-Values
! Thermal modeling and effective R-values
! Conclusions
! Slab edge support
Gravity Support Systems for Masonry Veneer
! Edge-connected steel angles
Gravity Support Systems for Masonry Veneer
! Discretely connected steel angles
Gravity Support Systems for Masonry Veneer
! Structural ! Weight of masonry ! Type of connection ! Backup structural capacity
! Eccentricity of load ! Section properties of
support member
! Deflection ! Design criteria
! Esthetics ! Secondary effects
! Seismic allowance ! Joint frequency ! Backup movement
Design Criteria
! Durability ! Material selection ! Compatibility of materials ! Environment conditions
! Thermal performance ! Design requirement
! Part 9 (small buildings) ! National Building Code of Canada (NBC), 2010
! New energy provisions within 2012 update to Section 9.36
! Provinces adopt the NBC with modifications
! City of Vancouver (VBBL) is adoption of BCBC
! Compliance is generally prescriptive (R-value tables)
! Part 3 (large buildings) ! NBC and Provincial codes reference both:
• National Energy Code for Buildings (NECB), 2011 – previously the MNECB 1997
• ASHRAE Standard 90.1 (Energy Code for Buildings Except Low-Rise Residential)
! Compliance path options (prescriptive, trade-off, modeling)
Overview: Canadian Energy Codes
Prescriptive Energy Code Requirements for Walls in Canada
Climate Zone
Wall – Above Grade: Minimum R-‐value (IP)
8 31.0
7 27.0
6 23.0
5 20.4
4 18.0 N
ECB
201
1 A
SH
RAE
90.1
-201
0 –
Re
side
ntia
l Bui
ldin
g Climate Zone
Wall (Mass, Wood, Steel): Min R-‐value
8 19.2, 27.8, 27.0
7A/7B 14.1, 19.6, 23.8
6 12.5, 19.6, 15.6
5 11.1, 19.6, 15.6
*7A/7B combined in ASHRAE 90.1 No climate zone 4 in ASHRAE 90.1 – bumped to zone 5
! Effective R-values are required to demonstrate compliance with Energy codes most of the time
! Nominal R-values do not include impacts of thermal bridging
! For example nominal R-20 batts within steel studs becoming ~R-9 effective, or in wood studs ~R-15 effective
! Masonry ties and shelf angles are also thermal bridges that reduce effective R-values significantly (even though a small area)
Effective vs. Nominal R-Values
! Effective R-values of Building Enclosure Assemblies can be determined by: ! Hand methods – simple wood frame walls, not
suitable for accounting for thermal bridges
! Laboratory (Guarded hot-box testing) – good for confirmation, expensive and not efficient for multiple configurations
! Two-dimensional finite element thermal modeling – not accurate for modeling discrete or intermittent elements such as thermal bridges
! Three-dimensional finite element thermal modeling – most accurate and cost effective. Calibrated with laboratory testing to improve accuracy.
! Heat3 (Blocon) – 3D finite element software used for this analysis
How are “Effective” R-values determined?
! Modeling performed to look at effective R-values for masonry veneer wall assemblies with alternate gravity support systems
! Steel stud backup, concrete backup, and exposed slab edge
Thermal Performance of Traditional Veneer Assemblies
Traditional Support Systems: Modelling Results
! Modeling performed to look at effective R-values for masonry veneer wall assemblies with alternate types of “stand-off” gravity support systems
! Knife plate, HSS Section, and overlapping angles
! Similar steel & mass and all connected at 48” o/c
Thermal Performance of “Stand-off” Supports Systems
“Stand-off” Support Systems: Modelling Results
Knife Plate HSS Structural Section
Overlapping Angles
shelf angle: 4”x4”x1/4” outside of insulation. 4”x4”x3/4” stand-off knife plates welded to embed plates at 48” o.c.
shelf angle 4”x4”x1/4” outside insulation. 4”x4”x1/4” HSS tube welded to embed plates at 48” o.c.
shelf angle 4”x4”x1/4” outside insulation. 2-6”x4”x5/16” angles bolted to slab edge at 48” o.c.
Nominal Insulation R-Value/U-Value
R-16.8 (RSI 2.95) U-0.060 (USI 0.339)
R-16.8 (RSI 2.95) U-0.060 (USI 0.339)
R-16.8 (RSI 2.95) U-0.060 (USI 0.339)
Effective Assembly R-Value/U-Value
R-14.8 (RSI 2.6) U-0.068 (USI 0.384)
R-14.8 (RSI 2.6) U-0.068 (USI 0.385)
R-15.0 (RSI 2.64) U-0.067 (USI 0.379)
Effective Reduction 16.4% 16.5% 15.3%
! Modeling performed to look at effective R-values for masonry veneer wall assemblies with alternate proprietary gravity support systems
Thermal Performance of “Proprietary” Supports Systems
Proprietary Support Systems: Modelling Results
Standoff Bracket 4-Bolt Cast-In
shelf angle 4”x4”x1/4” outside insulation. Proprietary clip is ¼” thick steel, 4”x4”x1/4” 6” long C-section. Non-welded connection.
Shelf angle 4”x4”x1/4” outside insulation. Pre-manufactured cast-in place thermal break connection with 4 stainless steel bolts attached to 7”x7”x 3/8” plate.
Nominal Insulation R-Value/U-Value
R-16.8 (RSI 2.95) U-0.060 (USI 0.339)
R-16.8 (RSI 2.95) U-0.060 (USI 0.339)
Effective Assembly R-Value/U-Value
R-14.9 (RSI 2.62) U-0.067 (USI 0.381)
R-16.4 (RSI 2.9) U-0.061 (USI 0.345)
Effective Reduction 16.4% 7%
Impact of Support Spacing
! Thermal bridging at masonry veneer supports is significant and alone can impact the effective wall R-value of an exterior insulated concrete wall by 27%
! Design details for “stand-off” conditions that are relatively typical in the industry reduce the overall impact of thermal bridging through continuous exterior insulation to 15-17%
! Special measures are possible, utilising proprietary systems to reduce the impact of thermal bridging below 10%
Conclusions
Questions
! Michael Wilson –[email protected]