building enclosure details and assemblies for wood-frame

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 – jpinon@rdh.com Colin Shane – cshane@rdh.com Brian Hubbs – bhubbs@rdh.com www.rdh.com

!  rdh.com

Discussion + Questions COLIN SHANE CSHANE@RDH.COM