walls that work: detailing for performance - woodworks€¦ · double top plate interior wall ......

Walls That Work: Detailing for Performance

Mary Uher August 27, 2014

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

Course Description

With wall systems serving so many functions in a building, they can be a challenge to effectively design. As a part of the structural and thermal envelopes, wood-frame walls are vital to building performance. Structural design must be balanced with the need for door and window openings and, at the same time, detailed to limit water and air infiltration. This program focuses on how to maximize wall performance while reducing cost through a combination of new design methods and time-tested details.

Learning Objectives

1. Understand load path continuity and shear wall performance including design methodologies for shear walls.

2. Apply moisture control methods for wood-framed wall systems to maximize their performance in the building envelope.

3. Identify installation considerations that may affect performance and determine how to address these issues proactively as part of the design.

4. Recognize how wood wall systems allow flexibility to adapt to future changes in owner or occupant needs.

Walls That Work: Detailing For Performance

! Load Path ! Framing Considerations ! Shear Walls ! Designing for Durability ! Energy Considerations ! Flexibility in Design

IBC 2012 1604.4 “Any system of method of construction to be used shall be based on a rational analysis in accordance with well established principles of mechanics. Such analysis shall result in a system that provides a complete load path capable of transferring loads from their point of origin to the load-resisting elements.”

Vertical Load Path Lateral Load Path

Load Path

1. Ridge Beam

2. Post

3. Header

4. Jack Studs

5. Sill Plate

6. Foundation

7. Ground

Load Path

Vertical (Gravity) Load Path Issues Load Load Load

Load Path

Lateral (Sideways) Load Path Issues Load Load Load

Shear W

all Shear W

all

Resisted by shear walls

Load Path Continuity

Resisted by Shear Walls

Racking

Resisted by Anchors

Base Shear

Resisted by Hold Downs & Dead Load

Overturning

Effects of Lateral Forces


Racking


Base Shear

Load Path Continuity 2003 Missouri Tornado

Overturning


Incomplete Load Path – Connections Are Key!

Wall Framing: Interior Wall Intersection Options

Ladder Junction Double top plate Interior wall 2x ladder blocking at 24"o.c.

Install blocking with wide face vertical for maximum backing to wall finish and for maximum

insulation in exterior walls.

Wall Framing: Interior Wall Intersection Options

Junction for Continuous Drywall Application

Drywall Interior stud set in 3/4 inch (or more) from exterior wall studs

Detail courtesy of NAHB Research Center

Double top plate

Wall Framing: Three-stud Corners

Insulated Three-stud Corner (California Corner) Difficult to insulate

Traditional Corner

Wall Framing: Two-stud Corners

Corner stud 2x Ladder Blocking at 24"o.c. or Drywall Clips

2x Ladder Blocking at 24"o.c. or Drywall Clips

Wall Framing: Wall Sheathing Installation

! Fasten panels as recommended with 8d nails

!  6" o.c. at all panel edges !  12" o.c. in the field

! Space panels 1/8" at all panel ends and edges

! Use 7/16 or 15/32 category panels, typically

! Some OSB panels alter strength-axis orientation to allow vertical placement with strength axis across studs

Recommendations for sheathing installation

!  Sized for 8, 9, 10 ft. walls

!  Eliminates blocking

!  Easy to inspect

!  Less air infiltration

!  More direct uplift and lateral load-path

Oversize Wall Sheathing

Using WSP for Combined Shear and Uplift

! Resist combined uplift and shear

! Lower Cost ! Reduced

Construction Time

Reference: APA SR-101 Design for Combined Shear and Uplift from Wind

Combined Shear and Uplift

Nail pattern at each stud

Uplift Nailing

Lumber ½” space

WSP Tension Splice

Nail pattern at rim joist Transfer Tension

with Studs

Tension Splice at Rim Joist

Wall Framing: Continuous Sheathing

0

2000

4000

6000

8000

10000

12000

0 0.5 1 1.5 2 2.5 3

Load

(lbf

)

Displacement (in.)

3d5b6b 100%2d

2,000 lbf

4,000 lbf

8,000 lbf

10,000 lbf

Diagonal bracing resists 31% of WSP load

WSP wall bracing – Base case

CS-WSP resists 88% more load than WSP bracing

CS-PF resists 174% more load than WSP bracing

6,000 lbf

APA Full-Scale 3D Wall Bracing Tests, Form T2007-73

Segmented 1.  Aspect Ratio for

seismic 2:1 2.  Aspect ratio up to

3.5:1, if allowable shear is reduced by 2w/h

SDPWS 4.3.5.1

Force Transfer 1.  Code does not

provide guidance for this method

2.  Different approaches using rational analysis are used

SDPWS 4.3.5.2

Perforated 1.  Code provides

specific requirements

2.  The capacity is determined based on empirical equations and tables

SDPWS 4.3.5.3

Shearwall Design Methods

Shear Wall Design

Specific nail size and spacing requirements

APA wood structural panels of specific grade and thickness Specific

stud species

Anchor bolts

Hold-down anchors

V

H H H v v

H

SDPWS 4.3.5.1 !  Only full height

segments are considered

!  Max aspect ratio !  2:1 – for seismic* !  3.5:1 – for wind

Aspect ratio applies to full height segment

Segmented (Traditional) Wood Shear Walls

Shear Wall With Openings Force Transfer Around Openings

SDPWS 4.3.5.2 !  Shear around

openings accounted for by strapping or framing based on a “rational analysis”

!  H/w ratio defined by wall pier

Aspect ratio applies to wall pier segment

H H v

WALL PIER

V

!  Hold-downs only at ends !  Extra calculations and added construction details (connections, strapping, & blocking)

!  Uses traditional design values

Shear Wall With Openings Force Transfer Around Openings

H H v

WALL PIER

V

Shear Wall With Opening – Perforated Shear Wall

SDPWS 4.3.5.3 !  Openings accounted for

by empirical adjustment factor

!  Hold-downs only at ends !  Uplift between hold

downs, t, at full height segments is required

H H v t

Aspect ratio applies to full height segment

V

Shear Capacity Adjustment

Equation for Perforated Shearwalls

Alternative to tabulated values of Co: Equations 4.3-5 and 4.3-6, 2008 SDPWS ! Allows more efficient perforated shear wall designs

! Actual area of openings ! Tabulated values are based on maximum opening

size !  Example: 1 door & 2 windows !  Table assumes windows are same height as door

!  Takes away panel shear area

Shear Capacity Adjustment

Equation for Perforated Shearwalls

Tabulated Shear Capacity Adjustment Factors(Co)

Wind v. Seismic Shear Walls

Wind Design: ! Gypsum strength at wall interior can be added

! 3.5:1 max. aspect ratio for WSP, 2:1 for gypsum

Seismic Design: ! Requires 3x framing more often (SDC D-F)

! 2:1 max. aspect ratio without penalty !  3.5:1 permitted with penalty (2w/h)

Suggested References

Site-Built Portal Frame Bracing Methods

APA Report TT-100

Portal Frame with Holdowns

Designing for Durability: High Wind

Reference: APA Report M310

Roof Sheathing Attachment Gable end connections Cladding attachment

Roof to wall connection

Wall to wall continuity

Wall sheathing attachment Wall sheathing continuity

Wall connection to sill plate

Sill plate anchorage

Gable-end Framing Hurricane Charley

Photo Credit: US Department of Housing and Urban Development

Gable-end Framing

Tie gable end walls back to the structure Gable end truss top chord

Tension-tie strap, attach with (8) 10d common nails, each end of strap

Roof Trusses

(3) 10d Common nails (typical)

2" x 4" continuous lateral brace @ 6' on center. Lateral brace sized to extend from end wall to over 3 interior trusses plus 6".

2x4 flatwise blocking between truss bottom chords

Gable end truss bottom chord

Components and Cladding Loads

Reference: ASCE 7-10 Chapter 30

Components and Cladding Loads

Reference: Requirements for Wall Coverings and Wind Pressures, APA publication TT-105

APRIL 2011 – NC TORNADOS

2011 - RALEIGH, NC

Flying Debris

Wall Sheathing

Siding fastener

s

Siding attachment at energy efficient corners

Attachment base for utility vents, siding trim, etc.

Nail Base For Siding

WSP Sheathing As A Nail Base

Plywood or OSB

Performance Category

Ring Shank Nails (Dia.)

Wood Screws (Gauge)

Smooth Shank and Screw Shank (Dia)

.097 .113 .120 .128 .135 #7 #8 #9 .113 .120 .128 .131

7/16 38 45 48 51 53 61 66 72 11 12 13 13

15/23 or 1/2 41 48 51 54 57 65 71 77 12 13 13 14

19/32 or 5/8 52 61 64 69 73 85 90 97 15 16 17 17

Withdrawal Load (Pounds)1

See APA TT-109 for footnotes and complete table

Reference: APA TT-109

Construction Tips for Building

Moisture Resistant Houses

Understanding Mold & Moisture Intrusion

Durability: Moisture Control

Reference: APA Report A500

Prevent Moisture Intrusion

Four D's of Wall Design

3. Drying

4. Durable

1. Deflection

2. Drainage

Layers of Protection

Proper Building Wrap Installation Details*

Tape all tears

12" overlap at corner and vertical joints

Cut and wrap at openings

Tape all joints with air-barrier tape

3" overlap at foundation

Wood structural panel

Overlap horizontal joints 6"-12"

Proper fasteners

* Consult building wrap manufacturer for installation details

BBH – Walls, Page 9

Prevent Moisture Intrusion

Improper water management

Meeting Energy Codes Burden is on the builder to produce structures that are: 1.  Cost-effective to build 2.  Strong and safe 3.  Energy efficient

Balancing Cost, Structure and Energy

Whole Building Design

Tips for Sealing Building Envelope

Seal Thoroughly The building envelope separates the interior

conditioned air spaces from the unconditioned

air spaces

Conditioned space

Crawlspace - Unconditioned

Attic - Unconditioned

Whole Building Design

In new construction, the walls of a structure present a great opportunity to prevent energy loss

Meeting Energy Codes with Prescriptive Assemblies

! New joint publication

between ICC and APA

! Advanced Framing options

for meeting R20 or R13+5

insulation values

Reference: APA Report P320

Meeting Energy Codes with Prescriptive Assemblies

Headers thermal path (4%) Studs and plates thermal path (21%) Cavity insulation thermal path (75%)

4%

75%

21%

Average R-Values for Wood and Steel Framed Walls

0 2 4 6 8

10 12 14 16 18

2x4 @ 16" 2x6 @ 16"

10.8

16.2

6.6 8.8

11.6 13.8

Wood with WSP Steel with WSP Steel with WSP + R5 Foam Wall configurations based on stud size and spacing using same level of cavity

insulation. Values developed from a study by the NAHB Research Center (RP02-9)

Rough Opening Placement The placement of openings in load-bearing walls and the layout of framing members above openings have significant impact on header sizing for advanced framing.

Minimum required materials to frame rough opening Structure above imposing tributary loads on header Potential increased header size - increased load from structure above Excess materials due to inefficient opening placement

Best Placement

36" wide opening

36" wide opening

36" wide opening

24" wide tributary load



Note: Jack studs may not be required if using wood structural panel headers.

Wall Panels

!  Faster construction time !  Less waste !  Ease of assembly

Appearance Flexibility

Ease of Additions

Questions?

Mary Uher (410) 730-9663

[email protected]

This presentation was developed by a third party and is not funded by WoodWorks or the softwood lumber check-off.

This concludes The American Institute of Architects Continuing

Education Systems Course

APA Web Site: apawood.org

Connecting building and design professionals with timely technical information and recommendations.

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walls that work: detailing for performance - woodworks€¦ · double top plate interior wall ......

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