Assembly and Detailing Considerations for Wood-Frame Building Enclosures

COLIN SHANE M.ENG., P.ENG. ASSOCIATE, SENIOR PROJECT MANAGER

RDH BUILDING SCIENCE INC.

APRIL 26, 2016

Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board.

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

“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.

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.

Presentation Outline

! Drivers for Taller & Larger Mass Timber Buildings

! Building Enclosure Best Practices & Lessons Learned

! Case Studies from Tilt-up to High-rise Wood Towers

The Building Enclosure

Image Credit: MGA - Wood Innovation

Design Centre

Timber Structure

A Condensed History of Taller Wood Buildings

!  Pre 1900s – many examples of tall mass timber

buildings up to ~9 storeys, many still around

!  Mid 1900s – building/fire codes changed –

restricting wood-buildings to 3-4 storeys

!  Mid 1990s to early 2000s, Western States allow

construction of 5 storeys wood frame (stick

built)

!  Past decade – Mass timber buildings in Europe/

UK/Oceania up to 15 storeys tall

!  Several recent initiatives in Canada & US to

allow for taller mass wood buildings up to 18

storeys (alternate solutions under existing

codes)

2014 - Wood Innovation Design Centre, BC

1900s era Tall Wood Buildings Across North America

‘Local’ Examples

18 storey wood, UBC

12 storey wood, Portland OR

10 storey wood, New York

Building Enclosure Wall & Roof Design Best Practices

Building Enclosure Design Fundamentals

!  Primary function of the Building Enclosure: Separate the exterior &

interior environments

!  Protect wood during construction &

in-service for life

!  Serves functional and aesthetic &

purpose

!  Controls heat, air, and moisture

transfer along with noise and fire

!  Designed to accommodate building

movement, structural loads, initial &

seasonal wood movement

!  Key passive design element for an

energy efficient & sustainable

building

What’s Different About Mass Timber?

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

Detailing for Wood Movement in Taller Wood

!  Wood shrinks as it dries and swells

when it gets damp (both liquid water

& humidity fluctuations)

!  Mass timber assemblies introduce

unique details & shrinkage can often

be greater than anticipated (more

wood to shrink)

!  Building height & differential

movement between assemblies/floors

!  Manufacturing of CLT/Glulam

~12-14% MC for adhesives to bond

!  Watch in-service wetting/high RH,

drying in service (low RH) and

seasonal fluctuations in RH

What We Have Learned from Mid-rise Wood

Building Enclosures for Mass Timber

!  Key Considerations:

!  Keep heavy timber components warm

and dry

!  Design assembly with the ability to dry

out if it was built wet or gets wet in-

service (vapor open)

!  Wood provides ~R-1/inch so still need

2-4 inches of extra insulation to meet

code

!  All insulation should be placed on

exterior of heavy timber panels along

with continuous air barrier/ WB

!  Heavy timber assemblies are actually

pretty simple & efficient compared to

other systems

Wall Design for Taller Wood Buildings

!  Key Considerations: Durability, Airtightness & Thermal Efficiency

!  Strategies:

!  Exterior or split-insulated wood walls

!  Thermally efficient cladding attachments through exterior insulation

!  Non-combustible & moisture tolerant cavity insulation

!  Non-combustible rainscreen claddings

Screws through insulation over split insulated wall

Various clip & rail systems through exterior insulation

Wall Design for Taller Wood Buildings

!  Taller stick frame & heavy timber panel buildings = less room for stud frame insulation

!  Challenges to meeting prescriptive R-value requirements without ‘continuous’ wall insulation

Energy Codes Targets for Commercial Buildings

Climate(Zone(

IECC(2012(Above(Grade(Walls:(Mass,(Steel,(Wood!!Min.!Eff.!R)value!

IECC(2015(Above(Grade(Walls:(Mass,(Steel,(Wood!!Min.!Eff.!R)value!

7( 16.4,(15.6,(19.6( 14.1,(15.6,(19.6(

6( 12.8,(15.6,(19.6( 12.5,(15.6(19.6(

5(&(4C( 12.8,(15.6,(15.6( 11.1,(15.6,(15.6(

4(A/B( 9.6,(15.6,(15.6( 9.6,(15.6,(15.6(

3( 9.1,(15.6,(15.6( 8.1,(15.6,(15.6(

2( 7.0,(13.0,(15.6( 6.6,(13.0,(15.6(

1( 7.0,(13.0,(15.6( 6.6,(13.0,(15.6(

Clim

ate

Zone

Some state by state & municipal differences depending on year of energy code adoption.

Based on Maximum Effective Assembly U-value Tables (C402.1.2 (2012), C402.1.4 (2015))

Residential Building R-values buildings similar or in some cases slightly higher

Getting to Higher Effective R-values

Baseline 2x6 w/ R-22 batts = R-16 effective

Exterior Insulation: R-20 to R-40+ effective •  Constraints: cladding attachment, wall

thickness •  Good durability

Deep/Double Stud/SIPs: R-20 to R-40+ effective •  Constraints

wall thickness •  Fair durability

Split Insulation: R-20 to R-40+ effective •  Constraints: cladding

attachment •  Good durability with

proper design

Cladding Attachment with Exterior Insulation

Thermally Efficient Clip & Rail Systems

Cladding Attachment with Exterior Insulation

Long Screws through Exterior Insulation

Wall Design for Taller Wood Buildings

Curtainwall systems

! Strategies (continued) !  Robust air-tight, water

resistant & breathable wall

membrane (AB/WRB)

!  Membrane compatibility

with glazing, roofing, and

other assembly materials

!  Simple integration with

glazing systems & other

penetrations

!  Watch details at interfaces

with mass timber structure

(movement, gaps)

Air Barriers Systems for Taller Wood Buildings

Vapor permeable self-adhered membranes

Liquid/fluid applied membranes

Taped/sealed rigid sheathing

Air & WRB Materials Considerations

Liquid applied membranes

Liquid applied membranes

Self-adhered sheet applied membranes

Careful with Materials for Taller Wood Buildings

!  Watch use of vapor impermeable materials over wood that is wet or could get wet !  Self adhered membranes !  Foam plastic insulations

!  Vapor diffusion wetting & drying ability for assemblies & details should always be assessed – ensure balance

!  Allow panels to dry both ways whenever possible

Exterior Insulation Selection

!  Rigid exterior foam insulations (XPS, EPS, Polyiso, closed cell SPF) are vapour impermeable (in thicknesses of 2”+)

!  Is the vapour barrier on the wrong side?

!  Does the wall have two vapour barriers, can it dry?

!  Can I remove the interior vapour barrier?

!  Semi-rigid/rigid mineral fiber insulation is vapour permeable, it simplifies many design concerns & and improves redundancy, allowing drying of incidental moisture to exterior

!  Vapor permeance properties of WRB/air barrier membrane is also very important

Why is Vapour Permeable Insulation Safer?

Outward vapor diffusion drying allowed through vapour open mineral wool, fiberglass or cellulose insulation on exterior

Outward vapor diffusion drying restricted by foam plastic insulation on exterior – even if enough insulation is installed to prevent condensation

Side by Side Drying Test – Vapour Open vs Closed

Side by Side Drying Test – Vapour Open vs Closed

Plywood Behind XPS – wet for 8 weeks

Plywood Behind Mineral Wool – dried within 8 weeks

Wood-Frame Assemblies – ‘Perfect’ Wall

Roofs…. And Many Lessons Learned

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

!  Design assembly with redundancy

for in-service drying

!  Slope structure where possible

!  Insulation on top - conventional or

protected membrane assemblies

!  Question the need for heavy timber

panels up here?

Conventional roof with tapered insulation over wood joists

Protected membrane roof over vented & tapered structure over CLT

Keep Wood Dry During Construction

!  Several taller & larger wood building projects in the PNW have had issues & delays during construction as a result of wet roofs & fungal contamination

!  Hence guidance for protection during construction, temporary roofs, immediate roofing, scheduling, built-in redundancy for drying

Keep Wood Dry & Use Appropriate Materials

Key Lessons: Don’t use paper faced insulation in contact w/ damp wood & drying through more than one layer of plywood can be too slow

Protect Roofs from Rain – But Not Too Late

Key Lessons: Do not treat wood floors/roofs like a concrete slab - do not let nail-lam get wet & do not assume it will dry out fast enough on its own.

Monitoring & Drying

Key Lessons: Drying of heavier timber wood roofs is possible during construction in wet climates but does take time and money

Redundancy & Scheduling

!  Design for the inevitable

to keep roofing and

project on schedule

!  Design roof assemblies

for redundancy and in-

service drying where

possible

Protection of CLT & NLT Panels During Construction

!  Pre-applied SBS roofing membranes applied to horizontal panels in factory

!  Laps torched onsite immediately after installation

Protection of Wood During Construction - Finland

We Can Do It Here Too

Protection of CLT During Construction

Protection of CLT During Construction

5 ply CLT – ½ Untreated & ½ Treated with water repellant

End grain is very absorptive

Splits, checks & joints that allow water past top layer can be problematic

Erect & roof as fast as possible to protect from rain to avoid delays

Water repellants can help reduce uptake into wood

A Little Protection Goes a Long Way

No Coating Water Repellent Stain

CLT & Tall Wood Case Studies

Ronald McDonald House

!  Women’s and Children’s Health Center Housing

!  4 Buildings & common areas, 3 storey tilt-up CLT Structure

Tilt-up CLT

Tilt-up CLT

Building Enclosure Assemblies - Walls

Tilt-up CLT Wall Assemblies w/ Masonry Veneer

!  Located in Prince George, BC @ UNBC

Campus - North America’s Tallest

Wood Building

!  6 ‘tall’ storeys (equivalent to

8 storey, 98’ tall)

!  CLT shear walls, glulam columns

with glulam beams and staggered

CLT floor & roof structure

!  Thermal performance design targets

(effective R-values)

!  R-40 roof

!  R-25 walls

!  R-5 wood curtainwall glazing

!  Pre-fabricated design for curtain wall

& infill walls

Wood Innovation Design Center (WIDC)

Michael Green Architecture (MGA) – Contractor: PCL Construction

Wood Innovation Design Centre (WIDC)

Design & Architectural Renders: Michael Green Architecture (MGA) Currently North America’s Tallest Wood Building at 96 feet tall (8 storey equivalent)

Wood Innovation Design Centre (WIDC)

Design & Architectural Renders: Michael Green Architecture (MGA)

WIDC – CLT/Glulam Movement & Exterior Walls

Plywood over end grain to apply AB/WRB membrane

Large movement joint at curtainwall & SIPs panel head (1/2” to 1”)

Horizontal wood (CLT & Glulams kept relatively dry during construction to minimize swelling

Infill Wall Design

!  Infill walls are pre-fabricated in factory

!  Critical to properly detail interface and seal panel joints (air leakage) to avoid issues

!  Wall control layers tie directly into curtain wall system – need for robust membrane and connection materials

!  Robust silicone WRB/AB membrane on exterior surface (applied in factory) ties nicely into curtainwall assembly

!  Make sure materials stick to each other!

Curtainwall to Infill Wall Interface

Aluminum Curtainwall Veneer Framing

Silicone Applied Liquid AB/WRB

Interior Air Seal at Joints

Silicone Transition Strip AB/WRB attached with silicone to curtain wall and wall membrane

LVL Framing

Charred fire-treated cedar cladding attached to plywood backup & cleat system over drained & ventilated rainscreen cavity

WIDC – Structure & Enclosure

Curtainwall & Wall Movement Joints

Flexible joint material at head & jamb

Slip structural connection

Wood Veneer Curtainwall/Windows

Charred Fire-Treated Cedar Panelized Cladding

John Boys, Nicola Log-works

Conventional Roof Assembly

R-40+ Conventional Roof Assembly – 2 ply SBS, 4” Stonewool, 4” Polyiso, Protection board, Tapered EPS (0-8”), Torch applied Air/Vapor Barrier(Temporary Roof), ¾” Plywood, Ventilated Space (To Indoors), CLT Roof Panel Structure (Intermittent)

Construction Photos by PCL/MGA/RDH

Conventional Roof Assembly

Construction Photos by PCL/MGA/RDH

WIDC

Photo: Ema Peters

WIDC

Photo: Ema Peters

18 Storey Mass Timber Hybrid

Acton Ostry Architects

Opportunity for Innovation in Prefabrication

Acton Ostry Architects Goal <1 floor per week installed and weathertight!

Opportunity for Innovation in Prefabrication

3 systems designed, prototyped & costed for project consideration: -  Wood framing -  Steel stud framing -  Lightweight pre-cast concrete

Similar design concept to unitized curtainwall with horizontal stack joints and ‘chicken head’

Wall Prefabrication Concepts & Trials

Wall Prefabrication Concepts & Trials

Stay Tuned…

!  Growing industry interest in the design & construction of both larger and taller mass timber buildings

!  Design of building enclosures for redundancy & drying – vapor open drying, air-tight and thermally efficient

!  Need to protect mass timber elements like CLT & NLT from wetting during construction – it is not like plywood or

solid lumber

!  Protect with the right membranes at the

right time

!  Design for redundancy where possible

!  Growing use of pre-fabricated elements

Summary – Onward & Upward with Wood

This concludes The American Institute of Architects Continuing Education Systems Course

Colin Shane – cshane@rdh.com

!  rdh.com

Questions & Discussion