Structural Thermal Bridging 18

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1 Structural Thermal Bridging 18 James A. D Aloisio P.E., SECB, LEED AP jad@khhpc.com Klepper, Hahn & Hyatt Structural Engineering (315) Landscape Architecture jad@khhpc.com Building Envelope Services

2 Brief Description Thermal bridging occurs when a conductive material extends through a thermal building envelope, which can result in energy loss, condensation, and other problems. Concrete and steel structural elements, which are within the realm of structural engineers, are some of the most significant contributors. Recent research and product development have led to a greater understanding of the problem as well as the development of effective solutions. We ll identify some of the most common types of structural thermal bridging and the magnitude of potential energy loss, and review several different types of available solutions including cost, design methodology, and effectiveness.

3 Learning Objectives 1. Realize the impact of structural details on energy code compliance. 2. Differentiate thermal bridging conditions that can have a significant effect on building energy loss vs. those that have minimal effect. 3. Compare and contrast the benefits and drawbacks of some of the design options available for mitigation of structural thermal bridging.

4 Agenda Introduction Basics of conductive heat transfer for structural engineers Six thermal bridging mitigation strategies Other thermal bridging conditions Questions and Answers

5 Building Envelope Basics Envelope Properties Cladding/Protection Drainage Plane Thermal Insulation Air Barrier Vapor Control Structure

6 Thermal Bridging Is conductive heat transfer through thermally conductive materials across a building envelope Is responsible for energy loss as well as potential for condensation and reduced occupant comfort Occurs with structural steel, cold formed steel, concrete, masonry, wood, and other materials Has not commonly been addressed by structural engineers in the U.S. - until recently Can be minimized if properly detailed

7 Basics of Heat Transfer Types of Heat Transfer: Conduction Convection Radiation

8 Turn R-Values on Their HEADS R is thermal RESISTANCE U is thermal TRANSMISSION (U.S. Units) U = 1 / R Silica Aerogel / Nanogel EPS - Expanded Polystyrene Cellulose Fiberglass reinforced plastic Fiberglass - batts W ood Framing Autoclaved Aerated Concrete Normal W eight Concrete Stainless Steel Carbon Steel Aluminum Gold Copper Silver R /inch U /inch

9 The R-Value is simply the amount of heat resistance R=1/U R-VALUE Inches of Aged Polyisocyanurate Insulation The U-Factor is the actual rate of heat flow through the assembly U=1/R U-FACTOR Inches of Aged Polyisocyanurate Insulation Reff = (Rmax- Rmin)/ln(Rmax/Rmin)

10 Conductive Heat Transfer Paths Series and Parallel Series: Add up R- values along the path of heat flow Parallel: Heat chooses path of least resistance

11 Steel Stud Thermal Bridging

12 Steel Stud Thermal Bridging Infrared scans can clearly identify building heat loss through steel studs. The Steel framing Alliance has a Design guide. Continuous rigid insulation eliminates thermal bridging.

13 Insulation Between Studs J. Straube, 2007, Building Science Corp. All studs 16 o.c.

14 Other Ways to Address Steel Stud Thermal Bridging Foam-Cap thermal breaks Slit-Web studs Tri-chord steel systems Delta Studs

15 Brick Relieving Angles

16 Concrete Balconies

17 Thermal Bridging and Condensation Steel Beam Concrete Balcony

18 Other Countries and Thermal Bridging All European Union countries have new energy codes Based on limiting carbon emissions of buildings for Kyoto Protocol Set limits of thermal bridging, varying with building types

19 Thermal Steel Bridging Insert in Modern Steel Construction March 12 Thermal Steel Bridging Task Committee A joint venture between ASCE s Structural Engineering Institute and AISC Free!

20 Pankow/AISC/ACMA/PIC Sponsored Research

21 NEU Research: Double Lap Splice Bolted Steel Conn s w/ FRP Shims

22 NEU Research: Roof Posts and Canopy Beams

23 NEU Research: Roof Posts and Canopy Beams

24 Six Strategies to Address Non-Stud Thermal Bridging Geometric Separation Intermittent Bridging Element Stainless Steel Bridging Element Nonconductive Thermal Shims Manufactured Structural Thermal Break Assemblies (MSTBA s) Insulative Coatings

25 Geometric Separation Steel Lintels Original Detail Modified Detail

26 Geometric Separation Framed Balconies Reduce penetrations through insulated building envelope

27 Intermittent Not Continuous Bridging Elements Original Detail: Continuous angle supporting wood roof blocking Modified Detail: Clip angle, 6 long, 24 o.c. supporting wood roof blocking

28 Intermittent Not Continuous Bridging Elements Original Detail Modified Detail

29 Intermittent Stainless Steel Bridging Elements Original Detail Modified Detail

30 Intermittent Stainless Steel Bridging Elements Original Detail U-Factor for 36 height = 0.44 Modified Detail U-Factor for 36 height = 0.13

31 Steel Shelf Angle Supporting Exterior Masonry Wythe Proprietary system for brick shelf angle support Comes in both galvanized & stainless steel

32 Non-Conductive Thermal Shims Original Detail: Base plate of steel post in contact with interior steel support beam Modified Detail: ½ thermoplastic shim plate between base plate and beam

33 Non-Conductive Thermal Shims Original Detail Modified Detail

34 Steel Lintel With Fiberglass Reinforced Plastic Separator

35 Fiberglass Reinforced Plastic Angle Used in Hung Steel Lintel High School Classroom Addition Upstate NY September 2009 **ONLY SUPPORTS 20 OF BRICK**

36 FRP Shims

37 Manufactured Structural Thermal Break Assemblies Original Detail: Steel cantilever beam attached directly to interior steel support Modified detail: MSTBA Between cantilever beam and interior steel support Steel-to-Steel MSTBA

38 Manufactured Structural Thermal Break Assemblies MSTBA Original Detail Modified Detail

39 Manufactured Structural Thermal Break Assemblies

40 Manufactured Structural Thermal Break Assemblies MSTBA s

41 Manufactured Structural Thermal Break Assemblies Syracuse University Manley Fieldhouse Ice Storage Addition 2012

42 Manufactured Structural Thermal Break Assemblies

43 Manufactured Structural Thermal Break Assemblies Concrete to Concrete MSTBA s

44 Syracuse, NY Concrete MSTBA

45 Manufactured Structural Thermal Break Assemblies

46 Insulative Coatings Paint with Aerogel added for conductive resistance R-4.1 per inch, applied mils = R-0.1 to 0.2 total Mainly used to reduce potential for condensation Requires surface prep, prime coat, and protection coat Apply to steel 24 inches out from insulation plane on interior and exterior sides Verify insulation properties of paint there are imposters! Photo credits: Greg Pope/Righter Group, Inc.

47 Single Wythe CMU Walls With Insulation Inserts Use lightweight concrete Consider using insulation inserts even in grouted and reinforced cores Minimize web areas with new ASTM C90 web requirements

48 Wood Thermal Bridging Condensation at low-heeled wood roof trusses Solutions: 1. Insulate around heels 2. Install insulated crown molding

49 Foundation Insulation Can save significant building use energy in heating climates not so much cooling May be required by Building Energy Codes Can increase occupant comfort Should define a continuous plane If provided, maintain continuity at slab edges Consider mineral fiber insulation ( rock wool ) Question for discussion: How much of this is the responsibility of the Structural Engineer?

50 Energy Loss at Top of Foundation Wall/Exterior Edge of Slab

51 Foundation Insulation: Outside, or Inside, or In Between

52 Foundation Insulation: Outside or Inside? Outside: Must protect top-down to 6 below grade Consider site conditions SOG can butt right up against foundation wall Insulation reduces footing depth required for frost protection Much less common Inside: No protection needed No need to consider site conditions SOG should be insulated at edge Insulation eliminates doing shallow frost protected foundations Much more common

53 Foundation Wall With Inner Insulation Wythe High School Classroom Addition October 2009 Elementary School Music Addition August 2009

54 lenging Conditions et Slab Maintain Edge Thermal Insulation Breaks Challenging Conditions to Door Thresholds Porches Balconies Decks Loading Docks Structural Slabs

55 Summary -Recommendations Minimize cross-sectional area of bridging elements, where structurally possible Minimize conditions of continuous bridging, substituting intermittent bridges Use stainless steel when feasible Work with architects to develop envelope details Use FRP shims when loads are low, MSTBA s for larger loads Show foundation insulation, when appropriate Consider thermal bridging in your design practice!

56 Let s See What We ve Learned 1. What are three benefits of reducing thermal bridging in a building? 2. Which building condition usually has the greatest thermal bridging energy loss? a) Rooftop grillage posts b) Continuous shelf angles c) Canopy support beams d) Brick ties 3. True or False: Stainless steel conducts heat significantly better than carbon steel.

57 Questions? Thank you for your time! James A. D Aloisio P.E., SECB, LEED AP jad@khhpc.com Klepper, Hahn & Hyatt Structural Engineering (315) Landscape Architecture jad@khhpc.com Building Envelope Services