The Role of Control Layers in Building Enclosure Design

Transcription

1 The Role of Control Layers in Building Enclosure Design COLIN SHANE M.ENG., P.ENG. ASSOCIATE, SENIOR PROJECT MANAGER OCTOBER 13, 2016 Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board. 1 of

2 Copyright Materials This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited. RDH Building Sciences Inc of

3 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.

4 Course Description Building enclosures are responsible for controlling heat flow, air flow, vapor flow and a number of other elements. Through a combination of building science fundamentals and current research, this presentation will explore design considerations associated with wood-frame building enclosures and the role of control layers. Discussion will focus on best practices for designing durable, energy-efficient enclosures using traditional light wood-frame construction.

5 Learning Objectives Review building science fundamentals and building enclosure design considerations for light wood-frame buildings. Explore the role of control layers in building enclosures for elements such as heat flow, bulk water intrusion and air flow. Discuss best practices for light wood-frame building enclosure design, detailing, and construction techniques. Explore the thermal benefits of utilizing wood-frame construction.

6 Outline Building science basics Water control Air control Heat control Wall assemblies options Roof assemblies options 6 of

7 Wood-frame Building Enclosure Design Guides 2011 Building Enclosure Design Guide Wood-frame Multi-Unit Residential Buildings Emphasis on best practices, moisture and new energy codes 2013 Guide for Designing Energy- Efficient Building Enclosures Focus on highly insulated woodframe assemblies to meet current and upcoming energy codes CLT Handbook 7 of

8 Building Enclosure Design Fundamentals Separate indoors from outdoors, by controlling: Heat flow Air flow Vapor diffusion Water penetration Condensation Light and solar radiation Noise, fire, and smoke While at the same time: Transferring structural loads Being durable and maintainable Being economical & constructible Looking good! 8 of

9 Building Science Basics 9 of

10 Control Functions of Building Enclosures Control Air Control Rain Building Enclosure Control Vapor Control heat 10 of

11 Trends in Building Enclosure Design Trend towards more energy efficiently building enclosures Air barriers now required in 2012 IECC and 2013 CEC Washington and Seattle are ahead of the curve Higher R-value requirements Thicker walls More insulation / less air leakage = less heat flow to dry out moisture Marginal assemblies that worked in the past may no longer work Amount, type and placement of insulations matters 11 of

12 Water Penetration Control Strategies 12 of

13 Rainscreen Cladding 13 of

14 Air Penetration Control Why? Code requirement Occupant comfort Moisture Energy Air holds moisture that can be transported and deposited within assemblies. Unintentional airflow through the building enclosure can account for as much as 50% of the space heat loss/gain in buildings. 14 of

15 Air Barrier Systems Air Barrier Systems Must: Be continuous, airtight, durable Resist structural loads Bridge joints across inter-story and drift joints Not negatively affect drying ability Air barrier is a system, not just a material Details are critical 15 of

16 Types of Air Barrier Systems Loose Sheet Applied Membrane Taped Joints & Strapping Sealed Gypsum Sheathing Sealant Filler at Joints Liquid Applied Silicone sealants and silicone membrane at Joints Sealed Plywood Sheathing Sealant & Membrane at Joints Sealed Sheathing Membrane at Joints Self-Adhered vapor permeable membrane Plywood sheathing 16 of with taped joints (good tape)

17 New Materials: Air Barrier/WRB Membranes Not all are created equal each has strengths and weaknesses: Need to match compatible sealants/tapes/membranes with each. Choice will depend on substrate, field conditions, tie-in details. 17 of

18 Test it? IECC option Requirement in some jurisdictions and for some government clients Applies everywhere for new construction in the state of Washington. Seattle has additional requirements of the test (commercial code, which includes multifamily residential). Construction Documents include Air Barrier, Pressure Boundary, and Area of Pressure Boundary 18 of

19 How do we measure it? 19 of

20 What are the results? No published data regarding air leakage test result General interest in results 2014 ASHRAE Annual Conference 20 of

21 What are the results? ASTM E779 Residential 25 Buildings > 1,000,000 sf 26% 35% Commercial Institutional 2009 SEC Excludes roofs and below-grade 39% 39% 10% Liquid Applied 19% 23% 10% Curtain Wall/Window Wall Sealed Sheathing Sheet Applied Storefront 21 of

22 What are the results? Average = 0.25 cfm/ft 2 Normalized Air Leakage (cfm/ft2) Liquid Applied Curtain Wall/Window Wall Sealed Sheathing Sheet Applied Storefront 22 of

23 What are the results? The code-maximum target of 0.40 cfm/ft 2 is not prohibitively difficult to achieve. Buildings not meeting the target: Contractor/developer did not prioritize the air barrier Significant discontinuities in the air barrier systems Companion buildings with similar designs, teams, or air barrier systems show overall improvement. HVAC and parapet detailing 23 of

24 Conductive Heat Loss Control Insulation between studs is most common heat control strategy Need to consider effective R-values Thicker walls and/or continuous exterior insulation on exterior becoming more common 24 of

25 Wood Framing Factor Impact 25 of

26 Insulation Placement Consider effective thermal resistance 26 of

27 Cladding Attachment Through Exterior Insulation 27 of

28 Cladding Attachment through Exterior Insulation Longer cladding Fasteners directly through rigid insulation (up to 2 for light claddings) Long screws through vertical strapping and rigid insulation creates truss (8 +) short cladding fasteners into vertical strapping Rigid shear block type connection through insulation, 28 of cladding to vertical strapping

29 Thermally Improved Performance Continuous metal Z-girts Fiberglass Clips & Hat-Tracks 29 of

30 The Perfect Assembly Rain penetration control: rainscreen cladding over water barrier Air leakage control: robust air barrier system Heat control: continuous insulation layer Locate all barriers exterior of structure Keep structure warm and dry 50+ year old concept! 30 of

31 Wood-Frame Assemblies Perfect Wall 31 of

32 Wood-Frame Assemblies Perfect Roof 32 of

33 Wall-to-Roof Detail 33 of

34 Wall Assemblies 34 of

35 Calculating One-Dimensional R- and U-values Appendix A ASHRAE Fundamentals Thermal Modeling Software 2x6 wood-framed wall with R-19 batts Effective R value =16 (16% loss) Effective U value = x6 metal framed wall with R-19 batts Effective R value = 9.3 Effective U value =0.106 (50% loss) 35 of

36 Wood Frame Wall Assemblies The Old Way Assembly ½ gyp 16 o.c. R-23 mineral fiber insulation ½ sheathing WRB/furring/cladding Standard framing factor 77% cavity, 23% framing U of

37 Wood Frame Wall Assemblies Option 1 Assembly ½ gyp 16 o.c. R-30 high density mineral fiber insulation ½ sheathing WRB/furring/cladding Standard framing factor 77% cavity, 23% framing U (R-22.0) 37 of

38 Wood Frame Wall Assemblies Option 2 Assembly ½ gyp 16 o.c. R-21 batt ½ sheathing 1 Mineral fiber insulation (R-4.2 continuous) Standard framing factor U (R-21.5) 38 of

39 Option 1 vs. Option 2 39 of

40 Sorption Isotherm 40 of

41 Roofs 42 of

42 Refresher: Low Slope Roof Types Protected Membrane (Inverted) Conventional Vented/Unvented (Compact) 43 of

43 The Perfect Roof Inverted / PMR / IRMA Control layers Water control - roof membrane Air control roof membrane Vapor control roof membrane Thermal control moisture resistant insulation Membrane directly on sloped structure Insulation above membrane Finish pavers, ballast Why is this perfect? 44 of

44 The Perfect Roof Inverted / PMR / IRMA 45 of

45 The Perfect Roof Inverted / PMR / IRMA 46 of

46 Conventional Roof Exposed Membrane Control layers Water control - roof membrane Air control Roof membrane? Or separate air barrier? Vapor control Roof membrane? Insulation? Or separate vapor barrier? Thermal control Rigid insulation Why is this less than perfect? 47 of

47 Case Study: Conventional Roof 2 ply SBS 4 Stone wool 4 Polyiso 0-8 EPS Taper Package for Slope Single ply SBS AB/VB & Temporary Roof Wood Deck Structure 48 of

48 Vented Roofs Control layers Water control - roof membrane Air control Interior drywall? Polyethylene sheet? Vapor control Roof membrane? Polyethylene sheet? Thermal control Batt insulation Why is this less than perfect? 49 of

49 50 of

50 51 of

51 52 of

52 Vented Roofs Why do we vent? To control air leakage / vapor diffusion condensation To dry out the plywood deck How does it work? Requires offset height to encourage convective looping in the space Warm moist air is replaced with dry exterior air How does it work in low sloped roofs? Who knows the wind? 53 of

53 Vented Roofs What increases moisture risk? More insulation More air leakage White membranes High interior moisture loads Wet venting air Good air barrier at ceiling and at wall-to-roof connection is critical Buyer (and designer) beware! 54 of

54 Summary 55 of

55 This concludes The American Institute of Architects Continuing Education Systems Course Colin Shane

56 Discussion + Questions Colin Shane cshane@rdh.com rdh.com 57 of