ud t di w dshikunderstanding wood shrinkage - · pdf fileud t di w dshikunderstanding wood...

U d t di W d Sh i kUnderstanding Wood ShrinkagePresented to:

C S2014 Chicago Wood Solutions Fair Presented by:

Doug Steimle | Schaefer

“The Wood Products Council”is a Registered Provider with The American Institute of

This course is registered with AIA CES for continuing professional education. AsThe American Institute of

Architects Continuing Education Systems (AIA/CES), Provider #G516.

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

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Course Description

• For condominiums, apartments, hotels and dormitories, multi-story wood construction is viewed by many as a way tostory 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 woodthese 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 g g ,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 ObjectivesLearning ObjectivesIdentify wood shrinkage characteristics of commonly used dimensional and engineered wood productsdimensional 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

Condominiums

ApartmentsApartments

HotelsHotels

Student Housing

Low Income HousingLow Income Housing

Mixed Use

The Banks

Why Design With Wood Framing?Why Design With Wood Framing?

Economical

Availability of material

It’s GreenIt s Green

Familiarity of owners, contractors and end users

Speed of construction

Future modifications can be made with relative ease

POLL QUESTION #1POLL QUESTION #1

• True or False:The root cause of the majority of shrinkage within a wood• 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 loadslive loads.

False:The compression of a properly engineered and constructed wood structure should be relatively minimal The majority ofwood 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 ShrinkageUnderstanding Wood Shrinkage

• Why does wood shrink?

Trees are living organisms, needing water to stay alive

A large component of wood is moistureA large component of wood is moisture

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

Understanding Wood ShrinkageUnderstanding Wood Shrinkage

• What happens when wood loses moisture content?

Wood shrinks

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

Characteristics of WoodCharacteristics of Wood

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


Characteristics of WoodAmount of Shrinkage for 30% Change in MC

Characteristics of Wood

Radial 4-5%

Tangential 7-8%

Longitudinal 0.1-0.2%

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


• 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 CalculationCode Required Shrinkage Calculation

• IBC 2304.3.3 Shrinkage. Wood walls and bearing titi h ll t t th t fl d fpartitions 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 plumbingadverse 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 shrinkagemovements caused by shrinkage…

S l Sh i kSample Shrinkage Calculation for Typical StoryStory

Typical Components

(1) 2x Sill Plate

StudStud

(2) 2x Top Plate

2x12 Joist

¾” Floor Sheathingg

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

Average Amount of Shrinkage for 30% Change in MC

Radial 4-5%

T ti l 7 8%Tangential 7-8%

Average for Shrinkage Perpendicular to Grain 6%

h2x4sill = (1.5 )(0.06)(6/30)

h2x4sill = 0.018Change in MC (16% to 10%)/30%

Sample Shrinkage Calculation for Typical StoryTypical Story

• Spruce Pine Fir 2x4x9’-0” Tall StudAverage Amount of Shrinkage for 30% Change in MC

Parallel to Grain 0.15%

h2x4stud = (108 )(0.0015)(6/30)

h2x4stud = 0.032Change in MC (16% to 10%)/30%


• Southern Yellow Pine 2x12 JoistAverage Amount of Shrinkage for 30% Change in MC

Radial 4-5%

Tangential 7-8%

Average for Perpendicular to Grain 6%

h2x12 joist = (11.25 )(0.06%)(6/30) h2x12 joist = 0.135 Change in MC (16%

to 10%)/30%


• ¾” Tongue and Groove OSB Floor SheathingExposure 1Exposure 1

Floor sheathing can swell up to 25% of its thickness during construction depending on the amount of moisture duringconstruction depending on the amount of moisture during construction (0.188” for ¾” sheathing)

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


• ¾” Tongue and Groove OSB Floor SheathingExposure 1Exposure 1

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

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

• h floor sheathing = 0.094”

Sample ShrinkageSample Shrinkage Calculation for Typical StoryStory

¾” Tongue and Groove OSB Floor Sheathing - Exposure 1Sheathing Exposure 1

Swelling of floor sheathing is very real. The shrinkage can also be assumed to gbe very real as well.

¾ Tongue and Groove OSB Floor

Sample Shrinkage Calculation for Typical Story

Sheathing

p g yp y

Sample ShrinkageSample Shrinkage Calculation for Typical StoryTypical Story

Three 2x4 Plates 0.054”

One 9’ 0” Stud 0 032”One 9 -0 Stud 0.032

One 2x12 Joist 0.135”

Floor Sheathing 0.094”

Total Shrinkage Per Story 0.315”

Consider revising gcalculation based on

conditions experienced while at

the site

Sample Shrinkage Calculation for Typical Storyp g yp y

POLL QUESTION #2POLL QUESTION #2

• True or False:In a multi story wood framed building the majority of• 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 extendsa building increases the higher the structure extends.

DiscussionDiscussion

• Where does shrinkage become a problem in the field?

Window ProblemsWindow Problems

• When a brick veneer is used in combination with a wood t t bl ft f llstructure, 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 theWhat happens when the windows move down and the veneer is moving up?

Window Problems

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

upon temperature and moisture content Brick arrives atupon temperature and moisture content. Brick arrives atthe site with the lowest moisture content it will ever have.

Thermal expansion can be as much as 0.028” for 11’ height e a e pa s o ca be as uc as 0 0 8 o e g tof 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 Sill

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

Remember that caulk is typically only 50% compressible.

Window Sill

Window Problems

Window SillWindow Sill

Window Problems

Window Sill

Window Problemsdo ob e s

Window Sill

Window Problems

Dimension needs to be two times estimated shrinkage


Joint is expandingJoint is expanding (widening)


Moving Down

Moving Up

Moving Down

Shear cracking in caulk jointj

Window Problems

Window Head and Jambs

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


Wi d J bWindow Jamb


Solutions to Window ProblemsSolutions 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 heightmoisture 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 ProblemsSolutions 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 movementdifferential movement.

Code Take on Window ProblemsCode 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 stressesLimits brick stresses

Limits anchor stresses

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

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

Anchored veneer can be engineered to exceed theAnchored 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 ProblemsBuilding Skin Problems

• Siding/Hardi-plank/plaster located over anchored brick veneerveneer

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 p j qthe hardi-plank or stucco to avoid problems with the hardi-plank or stucco

Building Skin ProblemsBuilding Skin Problems

Thin Set Veneer ProblemsThin Set Veneer Problems

Thin set veneers are adhered directly to the exterior h thisheathing.

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

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

Thin Brick over Anchored VeneerThin Set Veneer

Anchored Veneer

Other Common ProblemsOther Common Problems

Thin Set Veneer

Here is the result

Thin Set Veneer

Other Common ProblemsOther Common Problems

Plumbing Stack ProblemsProblems

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

Plumbing Stack ProblemsProblems

The horizontal tees that drain into the plumbing stacks typically travelthe 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 thethe 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 ProblemsPlumbing Stack Problems

Another potential contributing factor to possible problems ith l bi t k i i th th l i f thwith plumbing stacks is in the thermal expansion of the

plumbing stack itself.

Consider when plumbing stacks are installed on a projectConsider 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 wellwell.

Plumbing Stack ProblemsPlumbing 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 structurethe wood structure.

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

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

system.y

Vertical expansion joints

Require gap around horizontal plumbing runsRequire gap around horizontal plumbing runs

Avoid horizontal plumbing runs in structural studs

I f th l bi iInform the plumbing engineer

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

to the wood structure.Similar iss es can present themsel es hen steel framingSimilar issues can present themselves when steel framing is introduced in a wood structure.

Floor framing parallel to and adjacent to the CMU towerFloor 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 toResult is a sloped floor in the first joist space adjacent to the CMU tower.

This slope increases as the floor framing then deflects s s ope c eases as t e oo a g t e de ectsmid-span.

Masonry Stair or Elevator Tower ProblemsProblems

Masonry Stair or Elevator Tower RecommendationRecommendation

• 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 buildingMinimize amount of shrinkage in building.

Ways to Reduce ShrinkageWays to Reduce Shrinkage

Floor Trusses

AdvanTech

Protected WoodProtected Wood

During ConstructionDuring 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 ConstructionDuring 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 seasonsBe willing to take extra measures during wet seasons

Window Sill

Window Solutions

Shrinkage Summary• Anticipated Shrinkage Per Story Shrinkage Reducing

Recommendations

Shrinkage Summary


One 9’-0” Stud 0.032”

Recommendations

One 9 0 Stud 0.032

One Floor Truss 0.036”


Total Shrinkage Per Story 0.142”

Shrinkage Summary• Anticipated Differential Movement at Windows With

Shrinkage Reducing Recommendations

Shrinkage Summary


One 9’-0” Stud 0.032”

Shrinkage Reducing Recommendations



Brick Expansion 0 068”Brick Expansion 0.068

Total Differential Movement at Windows Per Story 0.210”

Shrinkage SummaryShrinkage Summary• Anticipated Differential Movement at Plumbing Stacks

With Shrinkage Reducing Recommendations


One 9’-0” Stud 0.032”

With Shrinkage Reducing Recommendations



PVC Plumbing Thermal Expansion (If installed at 20ºF) 0 165”PVC Plumbing Thermal Expansion (If installed at 20ºF) 0.165

Total Differential Movement at Plumbing Stacks Per Story 0.307”

Thank you for your time and your attention!attention!

Q ti ?Questions?

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

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