detailing for wood shrinkage - woodworks · detailing for wood shrinkage presented to: 2014 oregon...

Detailing For Wood Shrinkage Presented to:

2014 Oregon Wood Solutions Fair Presented by:

Doug Steimle | Schaefer Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or

the Softwood Lumber Board.

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."© Schaefer 2014

schaefer-inc.com

Course Description For condominiums, apartments, hotels and dormitories, multi-story wood construction is viewed by many as a way to achieve higher density at lower cost, while reducing the project’s carbon footprint. One of the challenges, in designing these taller buildings, is how to calculate and address wood shrinkage, which occurs as the wood dries from its ‘green’ state to its in-service equilibrium state. This session will examine shrinkage associated with wall and floor design, and demonstrate how to minimize effects of both shrinkage and differential movement with proper detailing. The discussion will include how to prevent shrinkage induced construction issues such as drywall cracking, window frame wracking, and compromised plumbing lines.

Learning Objectives !   Identify wood shrinkage characteristics of commonly used

dimensional and engineered wood products

!   Identify expansion/contraction characteristics of other materials in common buildings including veneers and PVC plumbing stacks

!   Identify conditions where differential movements within a building occur including window locations and plumbing stacks

!   Identify effective methods for limiting problems associated with differential movements

“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."

Condominiums

Apartments

Hotels

Student Housing

Low Income Housing

Mixed Use

The Banks

Why Design With Wood Framing? !  Economical

!  Availability of material

!  It’s Green

!  Familiarity of owners, contractors and end users

!  Speed of construction

!  Future modifications can be made with relative ease

POLL QUESTION #1 • True or False: • The root cause of the majority of shrinkage within a wood

building is due to compression/crushing of the wood members as a result of the applied combination of dead and live loads.

False: The compression of a properly engineered and constructed wood structure should be relatively minimal. The majority of shrinkage in a wood structure is due to a loss of moisture content in the wood members.

Understanding Wood Shrinkage • Why does wood shrink?

!  Trees are living organisms, needing water to stay alive

!  A large component of wood is moisture

!  Most “green” wood has a moisture content equal to 30% of its weight

Understanding Wood Shrinkage • What happens when wood loses moisture content?

!  Wood shrinks

!  This is the main reason why wood warps, checks, cups, etc.

Characteristics of Wood


Wood shrinks most in the radial and tangential directions. Very little shrinkage occurs in the longitudinal direction.

Amount of Shrinkage for 30% Change in MC

Radial 4-5%

Tangential 7-8%

Longitudinal 0.1-0.2%


•  30% change in moisture content is the maximum moisture change possible. This is from green (30% MC) to no moisture (0% MC).

Characteristics of Wood • Moisture Content

!  The amount of shrinkage experienced by a wood member is dependent upon the change in moisture content

!  Kiln dried lumber – typically 19% or lower moisture content

!  The drier the member is when installed, the less moisture will be lost in a finished structure and the less the member will shrink

Code Required Shrinkage Calculation •  IBC 2304.3.3 Shrinkage. Wood walls and bearing partitions

shall not support more than two floors and a roof unless an analysis satisfactory to the building official shows that shrinkage of the wood framing will not have adverse effects on the structure or any plumbing, electrical or mechanical systems, or other equipment installed therein due to excessive shrinkage or differential movements caused by shrinkage…

Sample Shrinkage Calculation for Typical Story

Typical Components

!  (1) 2x Sill Plate

!  Stud

!  (2) 2x Top Plate

!  2x12 Joist

!  ¦” Floor Sheathing

Sample Shrinkage Calculation for Typical Story •  Spruce Pine Fir 2x4 Plate (Sill or Top Plate)

!   Shrinkage perpendicular to grain affects change in height

!   Direction of grain in a member is dependent upon how it is milled

!   Therefore, take the average between tangential and radial shrinkage for shrinkage calculation (6% average)

!   Assume initial moisture content to be 16%, final moisture content to be 10%

Sample Shrinkage Calculation for Typical Story • Spruce Pine Fir 2x4 Plate (Sill or Top Plate) Average Amount of Shrinkage for 30% Change in MC

Radial 4-5%

Tangential 7-8%

Average for Shrinkage Perpendicular to Grain 6%

Ỏh2x4sill = (1.5�)(0.06)(6/30)

Ỏh2x4sill = 0.018� Change in MC (16% to 10%)/30%

Sample Shrinkage Calculation for Typical Story • Spruce Pine Fir 2x4x9’-0” Tall Stud

Ỏh2x4stud = (108�)(0.0015)(6/30) Ỏh2x4stud = 0.032�

Average Amount of Shrinkage for 30% Change in MC Parallel to Grain 0.15%

Change in MC (16% to 10%)/30%

Average Amount of Shrinkage for 30% Change in MC Radial 4-5% Tangential 7-8% Average for Perpendicular to Grain 6%

Sample Shrinkage Calculation for Typical Story • Southern Yellow Pine 2x12 Joist

Ỏh2x12 joist = (11.25�)(0.06%)(6/30)Ỏh2x12 joist = 0.135� Change in MC (16% to

10%)/30%

Sample Shrinkage Calculation for Typical Story • ¦” Tongue and Groove OSB Floor Sheathing#

Exposure 1

!  Floor sheathing can swell up to 25% of its thickness during construction depending on the amount of moisture during construction (0.188” for ¦” sheathing)

!  No published testing performed by APA regarding how much the product shrinks after the product swells and a load is placed on the sheathing (below a bearing wall)

Sample Shrinkage Calculation for Typical Story • ¦” Tongue and Groove OSB Floor Sheathing#

Exposure 1

!  APA help desk indicated to estimate a 50% reduction in swell thickness after drying and loading

• Ỏh floor sheathing = (0.75”)(0.25)(1/2)

• Ỏh floor sheathing = 0.094”


¦” Tongue and Groove OSB Floor Sheathing - Exposure 1 Swelling of floor sheathing is very real. The shrinkage can also be assumed to be very real as well.


¦� Tongue and Groove OSB Floor

Sheathing

Sample Shrinkage Calculation for Typical Story Three 2x4 Plates 0.054”

One 9’-0” Stud 0.032”

One 2x12 Joist 0.135”

Floor Sheathing 0.094”

Total Shrinkage Per Story 0.315”


Consider revising calculation based on

conditions experienced while at

the site

Shrinkage of Engineered Wood • Engineered wood, most commonly LVL’s, LSL’s, and PSL’s,

have very low moisture content when they leave the plant. The potential for shrinkage is low similar to OSB. However, they do have the potential to swell like OSB.

!  These products are likely to swell less than OSB though since they are not likely to have snow, ice and water sitting on them like floor sheathing.

!  These products can be utilized to help minimize total building shrinkage

POLL QUESTION #2 • True or False: •  In a multi-story wood framed building, the majority of

problems associated with wood shrinkage are observed at the lowest level of the building.

False: The shrinkage of a building is cumulative, the total shrinkage in a building increases the higher the structure extends.

Discussion • Where does shrinkage become a problem in the field?

Window Problems • When a brick veneer is used in combination with a wood

structure, problems often follow.

!  Windows are typically fastened to the wood structure.

!  The windows move as the wood structure moves.

!  What happens when the windows move down and the veneer is moving up?

Window Problems

Properties of Brick •  Brick is a clay product and can change size dependent upon

temperature and moisture content. Brick arrives at the site with the lowest moisture content it will ever have.

!  Thermal expansion can be as much as 0.028” for 11’ height of brick

!  Moisture expansion of brick can be as much as 0.040” for 11’ height of brick

!  Estimated total expansion of brick per story is 0.068”

Window Problems • Window Sill

!  Accommodations need to be made to allow for the differential movement. Otherwise, window will have operational difficulties.

!  Remember that caulk is typically only 50% compressible.

Window Problems

Window Sill

Window Sill

Window Problems

Window Problems

Window Sill

Dimension needs to be two times estimated shrinkage

Window Problems

Window Problems

Joint is expanding (widening)

Window Problems

Moving Up Moving Down

Shear cracking in caulk joint

Window Problems

This is the second story of a residence, the caulk joint has failed in both the jamb and head conditions

Window Head and Jambs

Window Problems

Window Jamb

Window Problems

Solutions to Window Problems •  Window Head and Jambs

!   The caulk joint needs to be designed for the potential differential movement or the caulk will fail. The caulk joints tend to fail on higher stories where differential movement is larger.

!   Consider specifying timeline for when to install caulk. The later the caulk joint is installed, the closer the building will be to its final moisture content and height.

!   Contractor may not be able to delay the caulk joint as it may prevent the ability to dry-in the building.

Solutions to Window Problems • Window Head and Jambs

!  Inform owner of potential problems with these joints. Maintenance should be expected on these joints due to differential movement.

Code Take on Window Problems •  Building Code Empirical Limits for Masonry Veneer Height

•  Addressed in Chapter 21 of IBC which refers to Chapter 6 of ACI 530/ASCE 5/TMS402

!   Prescriptive height limitations of anchored veneer with wood backup is 30 feet at height of plate and 38 feet at a gable.

!   Limits differential movement between wood structure and anchored veneer

!   Limits brick stresses

!   Limits anchor stresses

Code Take on Window Problems •  Building Code Empirical Limits for Masonry Veneer Height"

Addressed in Chapter 21 of IBC which refers to Chapter 6 of ACI 530/ASCE 5/TMS402

!  Anchored veneer can be engineered to exceed the prescriptive height limitations.

!  The primary concern with exceeding the prescriptive limits is in regards to detailing for the differential movement between the wood structure and the masonry veneer.

Building Skin Problems • Siding/Hardi-plank/plaster located over anchored brick

veneer

!  Often used by architect to change look of outside of building.

!  Has similar potential problems as at window sills

!  An expansion joint is required above the veneer and below the hardi-plank or stucco to avoid problems with the hardi-plank or stucco

Building Skin Problems

Thin Set Veneer Problems !  Thin set veneers are adhered directly to the exterior

sheathing.

!  When the wood structure experiences shrinkage, the veneer moves with the wood.

!  Check with the manufacturer for how much movement the thin set veneer can handle and the potential need for expansion/control joints.

Other Common Problems

Thin Brick over Anchored Veneer

Anchored Veneer

Thin Set Veneer

Thin Set Veneer

Here is the result

Other Common Problems

Plumbing Stack Problems What problems occur when the plumbing stacks travel vertically from the slab on grade through the roof?

Plumbing Stack Problems The horizontal tees that drain into the plumbing stacks typically travel through holes in the stud wall. If the holes are too big, there may be a structural problem with the stud. If the holes are too small, the plumbing tees may shear off as the wood structure shrinks and the plumbing stack does not go down.

Plumbing Stack Problems !  Another potential contributing factor to possible problems

with plumbing stacks is in the thermal expansion of the plumbing stack itself.

!  Consider when plumbing stacks are installed on a project. If it is very cold outside and the building is not enclosed or heated, the plumbing will be very cold when installed as well.

Plumbing Stack Problems •  Assume we have a PVC plumbing stack.

!   If the plumbing is installed in 20 degree weather and the final temperature of the building is 70 degrees, then there is a 50 degree Fahrenheit change in temperature

!   Resulting increase in the height of a plumbing stack = 0.19” per 11 foot height.

!   The same increase in temperature would result in a 0.02” increase in height of the wood structure.

!   This movement acts in the opposite direction as the wood shrinkage and exacerbates potential plumbing tee problems.

Plumbing Stack Solutions •  Incorporate differential vertical movement into the design of the plumbing

system.

!   Vertical expansion joints

!   Require gap around horizontal plumbing runs

!   Avoid horizontal plumbing runs in structural studs

!   Inform the plumbing engineer

Masonry Stair or Elevator Tower Problems • CMU stair and elevator towers shrink very little compared

to the wood structure."Similar issues can present themselves when steel framing is introduced in a wood structure.

!  Floor framing parallel to and adjacent to the CMU tower will shrink with the wood structure.

!  Result is a sloped floor in the first joist space adjacent to the CMU tower.

!  This slope increases as the floor framing then deflects mid-span.

Floor will slope

Masonry Stair or Elevator Tower Problems

Masonry Stair or Elevator Tower Recommendation • This is a problem that does not have a great solution.

!  Inform owner/construction manager of issue to manage expectations.

!  Minimize span of members framed parallel to CMU walls.

!  Minimize amount of shrinkage in building.

Ways to Reduce Shrinkage !  Floor Trusses

!  Swell Resistant Sheathing

!  Protected Wood

During Construction • Construction Observation Recommendations

!  Make sure the mason is aware of the amount of space required between the brick sill and the window sill

!  Check the dimension between the window sill and the masonry sill

!  Check the size of holes for plumbing penetrations made through vertical studs to ensure there is some ability to allow for differential movement

During Construction •  Construction Observation Recommendations

!   Specify that all lumber be protected from weather prior to installation

!   Make sure Structural Engineer gives you anticipated shrinkage movements per floor for window detailing purposes

!   Be willing to take extra measures during wet seasons

Window Solutions

Window Sill

Three 2x4 Plates 0.054”

One 9’-0” Stud 0.032”

One Floor Truss 0.036”

Floor Sheathing 0.020”

Total Shrinkage Per Story 0.142”

• Anticipated Shrinkage Per Story Shrinkage Reducing Recommendations

Shrinkage Summary

Three 2x4 Plates 0.054” One 9’-0” Stud 0.032” One Floor Truss 0.036” Floor Sheathing 0.020” Brick Expansion 0.068”

Total Differential Movement at Windows Per Story 0.210”

• Anticipated Differential Movement at Windows With Shrinkage Reducing Recommendations

Shrinkage Summary

Three 2x4 Plates 0.054” One 9’-0” Stud 0.032” One Floor Truss 0.036” Floor Sheathing 0.020” PVC Plumbing Thermal Expansion (If installed at 20ºF) 0.165”

Total Differential Movement at Plumbing Stacks Per Story 0.307”

Shrinkage Summary • Anticipated Differential Movement at Plumbing Stacks

With Shrinkage Reducing Recommendations

This concludes The American Institute of Architects Continuing

Education Systems Course""

Questions?

schaefer-inc.com

Doug Steimle [email protected]

detailing for wood shrinkage - woodworks · detailing for wood shrinkage presented to: 2014 oregon...

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