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Building Enclosure Details and Assemblies for Wood-Frame Buildings COLIN SHANE M.ENG., P.ENG.
ASSOCIATE, SENIOR PROJECT MANAGER
RDH BUILDING SCIENCES INC.
Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board.
SEPTEMBER 16, 2015
“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.
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. 2015
Copyright Materials
Course Description
! This presentation will provide an in-depth look at a variety of wood-frame building enclosure assemblies and details. Beginning with a review of building enclosure design fundamentals and considerations, it will then focus on best practices with references from technical guidelines and case studies. Finally, the critical detail interfaces between different enclosure assemblies (i.e., walls, roofs, balconies, windows, foundations) will be reviewed with a focus on continuity of critical barriers. A series of details and case studies will be presented for each.
Learning Objectives
• Review building enclosure design best practices for light wood-frame buildings.
• Demonstrate effective methods of controlling heat, air, and moisture movement through wood-frame assemblies.
• Discuss common details used for light wood-frame wall and roof enclosure assemblies.
• Using case studies and details from past projects, demonstrate unique considerations and best practices associated with the interfaces between adjacent enclosure assemblies
! 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!
Building Enclosure Design Fundamentals
Bigger Buildings - Enclosure Considerations
! Greater exposure to driving rain & surface water run-off
! Need for better water control & details
! Increased wind pressures
! Need for more robust air barrier systems, higher performance windows, cladding attachments, roof uplift
! More structural framing & mass
! Less space for insulation within stud cavities – need for exterior insulation
! Hybrid wood/steel/concrete interfaces and connections
! Non-combustible claddings & enhanced fire-safety considerations
! Not just a house anymore!
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!
Wood-Frame Assemblies – ‘Perfect’ Wall
Wood-Frame Assemblies – ‘Perfect’ Roof
Wood-Frame Assemblies – ‘Perfect’ Roof
Wall-to-Roof Detail
Wall-to-Roof Detail
Continuity of Control Layers
! In practice, need to
evaluate and design
assemblies and details that
are not ‘perfect’
! Continuity of control layers
within and between
assemblies is critical
! Hygrothermal analysis?
Interfaces & Challenges – Balconies & Roofs
The Engineer’s Solution
The Other Engineer’s Solution
! Focus on continuity of control layers
! Need to understand
construction and sequencing
! Understand behaviour of
wood: movement and
shrinkage
! Details:
! Balconies
! Roofs and parapets
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 wood-frame assemblies to meet current and upcoming energy codes
! CLT Handbook
Design for Wood-Movement & Shrinkage
Behaviour of Wood in Construction
Wood Moisture Content vs Relative Humidity
Initial MC
Site/Construction
In-Service (Low)
In-Service (High)
Wood shrinkage is 0.20% to 0.25% in dimension per 1% change in MC
Behaviour of Wood in Construction
! Wood-frame Shrinkage
! Total shrinkage dependant on amount of tangential/radial grain wood and initial moisture content
! Differential movement is a real concern when detailing, especially for taller wood-frame buildings
! Shrinkage generally in range of ¼” per floor in dry cases, ½” per floor in typical cases, ~1” per floor in extreme cases
Cumulative Shrinkage for 6 storey Wood-frame Building at roof eave
Behaviour of Wood in Construction
! Detailing for Differential Shrinkage is Important…
Think of the effect that this also has on plumbing and other services running through walls
Window Gutters?
Lessons Learned from Wood-frame Shrinkage
Lessons Learned from Wood-frame Shrinkage
Window Sill Detail – Sealant Joint Method
But watch sealant compression stresses
Window Sill Detail – Sliding Flashing Method
Window Sill Detail – Sliding Flashing Method
Balconies & Slope
Reducing Wood-frame Shrinkage - Floors
! Keep wood dry, watch saturation of floor framing during construction
! Engineered floor joists
! Modified platform framing practices
! Floor joists hang from top plate of wall, essentially reducing shrinkable wood at floor line
! Balloon framed details
Reducing Effects of Differential Shrinkage
! Fire-rated wood-framed stairwell & elevator shafts instead of concrete or concrete block
! Have run into issues with this detail with some AHJs and fire-testing currently underway to demonstrate suitability
Adapting Design & Architectural Style
Balcony Designs
Wood-Framed Balcony
! Likely the most common framing method
! Questions:
! Where is the air barrier?
! Thermal barrier?
! Water barrier?
! ‘Saddles’?
! Do we vent?
! Guardrail attachment?
Cantilevered Balcony – Control Layers
! Air barrier:
! Use the shortest path possible
! Prevent interior air from entering balcony soffit
! Vent soffit
! Thermal barrier:
! Remember ‘perfect’ wall
! Water barrier:
! Over a sloped and drained balcony surface
Cantilevered Balcony - Saddles
Can you spot them?
Cantilevered Balcony - Saddles
! 3-dimensional integration of assemblies
! Include a 3-dimensional detail
Cantilevered Balcony
Pre-Finished Steel Balcony over Wood
! Balcony is a ‘bolt-on’ architectural component, but not part of building enclosure
! Air, water, and thermal control layers continuous behind pre-finished balcony
! Simplifies detailing – no saddles
! Use durable materials
Pre-Finished Steel Balconies
Roof Designs
Roof Design for Larger Wood Buildings
! Key Considerations: Keep dry, allow to dry, robustness of assemblies, sloping
strategy
! Strategies:
! Protect wood roof from getting wet during
construction
! Insulation on top of air and vapor control
layers - conventional or protected
membrane assemblies
! Connect control layers at walls
! Be cautious of interior insulated approaches, with or without venting
Conventional roof with tapered insulation over wood joists
Protected membrane roof over vented & tapered structure over CLT
Attics & Vented Roofs – Control Layers
! Likely the most common assembly in USA for sloped roofs – good track record in most climates
! Be cautious if used on low-slope roofs, particularly if venting path is complicated
! Air barrier continuity at ceiling at and roof-to-wall is critical
Roof to Wall – Control Layers
! Air barrier:
! Use the shortest path possible
! Ideally below parapet framing
! Thermal barrier:
! Ideally to exterior of control layers
! Water barrier:
! Roof membrane to sheathing membrane
Roof to Wall – Control Layers
! Air barrier:
! Use the shortest path possible
! Ideally below parapet framing
! Thermal barrier:
! Ideally to exterior of control layers
! Water barrier:
! Roof membrane to sheathing membrane
Interfaces & Challenges - Parapets
Air Barrier Details
! Pre-stripping AB membrane is often recommended at framing interfaces & roof-wall transitions – but often forgotten!
Air Barrier Details
Summary
! Control moisture, air, and heat
! Best practices:
! Rainscreen cladding
! Keep structure warm and dry: control layers on exterior
! Think about the details!
! Provide continuity of control layers within and between assemblies and details
! Easier said than done: modern large buildings often architecturally complicated
! Walls, roofs, balconies, and…?
This concludes The American Institute of Architects Continuing Education Systems Course
Joe Piñon – [email protected] Colin Shane – [email protected] Brian Hubbs – [email protected] www.rdh.com
! rdh.com
Discussion + Questions COLIN SHANE [email protected]