Design Considerations for Durable Wood Structures

Transcription

1 Design Considerations for Durable Wood Structures

2 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 CESfor 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.

3 Course Description With proper design, detailing and specification, wood structures can provide long and useful service lives while also offering a reduced environmental footprint. The key is careful planning and understanding of environmental loads and other external factors likely to impact a building over its lifetime. This presentation provides an overview of considerations related to durable wood design, including moisture management techniques, preservative treatment specification, and details for controlling termites.

4 Learning Objectives 1. Determine methods for controlling moisture infiltration into the exterior wall assemblies. 2. Review good building envelope detailing practices including guidance on the use of water, air and vapor barriers. 3. Discuss specification of preservative treated and naturally decay resistant wood material. 4. Introduce termite prevention strategies.

5 Outline Building Examples Potential Building Hazards Understanding Wood Moisture Control Durable Materials Controlling Termites Service Life

6 Outline Building Examples Potential Building Hazards Understanding Wood Moisture Control Durable Materials Controlling Termites Long Service Life

7 Borgund Stave Church Borgund, Norway Built between

8 Tōdai-ji, Buddhist Temple Nara, Japan Built 752 and Rebuilt 1709

9 Butler Brothers Building Architect: Harry W. Jones Built 1906 and Renovated 1974

10 The Cathedral of Christ The Light, Oakland, CA, USA Design Team: Skidmore Owings & Merrill, Craig W. Harman, Webcor Builders Photo Credit: Timothy Hursley, Cesar Rubio, and John Blaustein,

11 Arena Stage, Washington, DC Architect: Bing Tom Photo Credit: Nic Lehoux

12 Outline Building Examples Potential Building Hazards Understanding Wood Moisture Control Durable Materials Controlling Termites Long Service Life

13 Potential Hazards MOLD Fungi Does not significantly effect structural properties of wood Some associated with occupant health concerns MOLD effects all materials!

14 Potential Hazards DECAY Fungi Can degrade structural capacity Do not cause health concern RUST and ERROSION are potential hazards too.

15 Potential Hazards INSECTS Wood boring beetles Carpenter ants Termites Damp-wood termites rarely a problem for buildings Dry-wood termites only in extreme southern US and Mexico Subterranean termites very controllable risk Formosan termites more aggressive, exist in southeastern US Wood Boring Beetles Carpenter Ants Formosan Termite Know your risk based on geography and design for it.

16 Not Hazards Staining Fungi Weathering

17 Potential Hazards Mold Decay All Organic Life Requires: Insects 1. Oxygen 2. Food Source 3. Moderate Temperature 4. Moisture

18 Outline Building Examples Potential Building Hazards Understanding Wood Moisture Control Durable Materials Controlling Termites Long Service Life

19 Understanding Wood: Hygroscopic Free Water VS Bound Water Fiber Saturation Point: Point at which cell walls are completely saturated, cell cavities are empty (i.e. no free water but still has all its bound water)

20 Understanding Wood: Hygroscopic Moisture Content Fiber Saturation = 28% MC Code required to be < 19% MC at building close Wood still has ability to absorb water between 19-28% Picture Source: Panshin, A.J. and de Zeeuw, C., (1980) Textbook of Wood Technology, Fourth Edition, McGraw-Hill, inc.

21 Understanding Wood: Orthotropic Wood is orthotropic, meaning it behaves differently in its three orthogonal directions: Longitudinal (L), Radial (R), and Tangential (T) This is a direct result of the arrangement of wood cells

22 Outline Building Examples Potential Building Hazards Understanding Wood Moisture Control Bulk Water Intrusion Air flow Current Vapor Diffusion Durable Materials Controlling Termites Long Service Life

23 Moisture Control Wetting Drying Bulk water intrusion Air current induced moisture vapor movement Vapor migration by diffusion Evaporation or diffusion Directionally effected by humidity, temperature and pressurization

24 Moisture Control Wetting Drying Bulk water intrusion Air current induced moisture vapor movement Vapor migration by diffusion Evaporation or diffusion Directionally effected by humidity, temperature and pressurization

25 Durability By Design

26 Deflection Source: Moisture and Wood Framed Buildings by CWC

27 Deflection Source: Moisture and Wood Framed Buildings by CWC

28 Deflection Overhang Ratio Overhang Width Wall Height Source: Moisture and Wood Framed Buildings by CWC

29 Deflection Source: Moisture and Wood Framed Buildings by CWC

30 Barrier Wall System Source: Moisture and Wood Framed Buildings by CWC Example: Commonly masonry (veneer) facades are face sealed and may not have a path for drainage behind.

31 Concealed Barrier Wall System Example: All joints and seams in sheathing sealed with compatible and durable tape and façade directly attached. Source: Moisture and Wood Framed Buildings by CWC

32 Rainscreen Wall System Example: In addition to furring strips, dimpled mats, crinkled housewrap or textured mesh can also provide a drainage plain an capillary break. Source: Moisture and Wood Framed Buildings by CWC

33 Vented Rainscreen Wall System Source: Moisture and Wood Framed Buildings by CWC Example: Furring strips fastened to framing through insulating sheathing with openings at top and bottom provided with screen to prevent insect entry.

34 Durability by Design - Guide to Barriers Weather Barrier Address bulk water that gets past cladding Applied at exterior Ex: building papers/wraps (NOT all) Limits liquid water passing through Air Barrier Stops movement of air under pressure Applied at interior or exterior Ex: Board stock, tapes Vapor Barrier/Retarder Slow movement of water vapor by diffusion Installed on warm side of insulation May not be required or desired Low level of permeability

35 Weather Barriers Perforated House wraps Unperforated House wraps Building Felt/ Paper Water Resistant Less than unperforated Yes Yes, varies greatly Vapor Permeable Yes Yes Yes Air Resistant Yes Yes Only if penetrations are all sealed Moisture Absorptive No No Yes, varies greatly Tear Resistant Yes Yes Varies greatly UV Resistant Varies greatly Varies greatly No Moisture Tolerant Yes Yes No

36 Durability By Design Reservoir Cladding Reservoir cladding systems need an airspace to dry and eliminate capillary action.

37 Durability by Design - Stucco Moisture load at window header, sills and corners Need to minimize ability to store water

38 Durability by Design - Stucco Ensure clean sand is used in Stucco mix. Specify building wrap with built in drainage or two layers of building wrap.

39 Durability by Design Brick Veneer Provide minimum 1 airspace behind brick veneer.

40 Durability by Design Brick Veneer Provide a path for drainage get out from behind the wall.

41 Durability By Design Detailing DO NOT X-cut Building Paper at Window.

42 Durability By Design Detailing

43 Durability By Design Detailing Avoid Horizontal Valley s. 1 of RAIN 2000 sq ft of ROOF 1250 gallons of WATER

44 Durability By Design Detailing Flash at roof and wall intersections.

45 Moisture Control Wetting Drying Bulk water intrusion Air current induced moisture vapor movement Vapor migration by diffusion Evaporation or diffusion Directionally effected by humidity, temperature and pressurization

46 Moisture Control - Condensation Change in relative humidity (rh) of air at 70F cooled to 35F (with no moisture added or removed)

47 Moisture Control - Condensation 70 Degrees F 30% Relative Humidity Dew Point Location INSIDE OUTSIDE Dew Point 0 Degrees F

48 Moisture Control Air Current Source: Building Science Corporation

49 Moisture Control Insulation Steel may be hard to insulate: Wood insulation example:

50 Moisture Control Air Sealing Ease of installation Addresses Windwashing Controlling moisture loads Exterior Air Barrier No intersecting walls and fewer penetrations Prevents windwashing of the cavity insulation Control entry of exterior hot humid air into insulated cavities in hot humid climates. Interior Air Barrier More intersecting walls and penetrations to detail around Using semi-rigid insulation can prevent the need to address wind-washing Control entry of interior moisture laden air into insulated cavity during heating

51 Moisture Control Wetting Drying Bulk water intrusion Air current induced moisture vapor movement Vapor migration by diffusion Evaporation or diffusion Directionally effected by humidity, temperature and pressurization

52 Moisture Control - Vapor Diffusion Vapor Diffusion Moisture transfer through a material moving from wetter to dryer Vapor Pressure is the weight of the water in the air. Higher humidity air weighs more creating a pressure that move water from wetter to dryer

53 Moisture Control Vapor Retarders Vapor Retarders: Class I perm or less Class II less than (or equal to) 1.0 perm and greater than 0.1 perm Class III less than (or equal to) 10 perm and greater than 1.0 perm Vapor Barrier = Class I Source: Building Science Corporation

54 Moisture Control Vapor Retarders Source: IECC Climate Zone Map

55 Moisture Control Vapor Retarders Zone 1-3 Do not require any class of Vapor retarder on the interior surface of insulation in insulated wall and floor assemblies Zone 4 (except Marine) Do not require any class of Vapor retarder on the interior surface of insulation in insulated wall and floor assemblies Zone 4 (marine), 5-7 Class II or III (or lower) may be required depending on permeance of sheathing and cladding. Higher class can be applied if dew point is controlled (requires modeling).

56 Moisture Control Climate Zones Source: Build America US Department of Energy (

57 Moisture Control Good Example Applicable to Mixed-humid Hot-humid Mixed-dry Hot-dry Marine Some colder regions (5/6) NOT applicable to: Very cold Subarctic/arctic Source: Building Science Corporation

58 Moisture Control Good Example Applicable to Mixed-humid Hot-humid Mixed-dry Hot-dry NOT applicable to: Marine Cold Very cold Subarctic/arctic Source: Building Science Corporation

59 Moisture Control Good Example Applicable to: Cold Very cold NOT Applicable to Marine Mixed-humid Hot-humid Mixed-dry Hot-dry Subarctic/arctic Source: Building Science Corporation

60 Moisture Control Good Example Applicable to: Marine Cold Very cold NOT Applicable to Mixed-humid Hot-humid Mixed-dry Hot-dry Subarctic/arctic Source: Building Science Corporation

61 Outline Building Examples Potential Building Hazards Understanding Wood Moisture Control Durable Materials Preservative Treatment Naturally Decay Resistant Controlling Termites Long Service Life

62 Preservative VS Pressure Treated

63 Preservative Treated As defined by the IBC in Chapter Preservative-treated wood. Lumber, timber, plywood, piles and poles supporting permanent structures required by Section to be preservative treated shall conform to the requirements of the applicable AWPA Standard U1 and M4 for the species, product, preservative and end use. Preservatives shall be listed in Section 4 of AWPA U1. Lumber and plywood used in wood foundation systems shall conform to Chapter 18. However code compliant preservative treated products can also follow: Alternate materials and methods ICC reports can also be provided for proprietary treatments and products under this provision

64 Source: Guide to Pressure Treated Wood, WWPI Preservative Treated - Specification

65 Preservative Treated - Specification ICC reports can also have a lot of information that can be useful in specification for both proprietary and non proprietary treatments. Conditions of use Fastener recommendations Structural capacity

66 Preservative Treated Treatment Types Waterborne Copper Based: ACQ Alkaline Copper Quat ACZA (Chemonite) Ammoniacal Copper Zinc Arsenate CA Copper Azole CCA Chromated Copper Arsenate PTI and EL 2 Carbon-based preservatives MCA Micronized Copper Azole Borate Based: SBX Inorganic Boron Oil based Pentachlorophenol Copper Naphthenate Creosote

67 Preservative Treated - Incising Pressure-treated Douglas-fir Pressure-treated Southern Pine Photo from University of Tennessee Forest Products Extension

68 Preservative Treated Spec Examples 1. Sill plates shall be treated in accordance with AWPA Standard U1 to the requirements of Use Category 2 (UC2). 2. Sill plates shall be treated with waterborne preservatives in accordance with AWPA Standard U1 to the requirements of Use Category 2 (UC2). 3. Sill plates shall be treated with waterborne preservatives in accordance with AWPA Standard U1, Commodity Specification A, to the requirements of Use Category 2 (UC2). 4. Sill plates shall be southern pine lumber, treated with waterborne preservatives in accordance with AWPA Standard U1, Commodity Specification A, to the requirements of Use Category 2 (UC2). 5. Sill plates shall be southern pine lumber, treated with inorganic boron (SBX) in accordance with AWPA Standard U1, Commodity Specification A, to the requirements of Use Category 2 (UC2). Proprietary Treatments specification guidelines are usually very clearly provided by the treated product supplier on their website.

69 Preservative Treated - Fasteners IBC Hot-dipped galvanized steel above grade Stainless steel below grade, salt-water exposure, severe conditions Silicon bronze Special use Copper Special use

70 Preservative Treated LCA Comparison Source: Conclusions and Summary Report on an Environmental Life Cycle Assessment of Borate Treated Lumber Structural Framing with Comparisons to Galvanized Steel Framing, Treated Wood Council 2012

71 Preservative Treated Field Treatment Copper Napthenate At least 2% copper solution Available field treatment products Copper-Green Copper-Green Brown Wood life Copper Coat Copper Care Cu-Nap Concentrate Armor All End Cut Wood Preservative

72 Preservative Treated Wood Products Solid Sawn Plywood Glulam Parallel Strand Lumber

73 Naturally Decay Resistant Species Source: US Forest Products Lab Wood Handbook Chapter 14 Biodeterioration, Clausen 2010

74 Cell Structure: Heartwood & Sapwood Sapwood: Outer, lighter colored band which conducts moisture and sap, stores biochemicals and carbon, and is the metabolically active zone (living sapwood cells are agents of heartwood formation)

75 Cell Structure: Heartwood & Sapwood Heartwood: darker colored core, long term storage of extractives which are biochemicals that provide natural durability to wood. They are formed at the heartwood-sapwood interface and infiltrate cells throughout the heartwood region

76 Outline Building Examples Potential Building Hazards Understanding Wood Moisture Control Durable Materials Controlling Termites Long Service Life

77 Controlling Termites

78 Controlling Termites: Subterranean 2006 Map Subterranean Termite Hazard Severity Subterranean Termites Their Prevention and Control in Buildings, US Forest Service 2006

79 Controlling Termites: Formosan Territory Source:

80 Durability Detailing The 6S Approach to Subterranean Termite Control Suppression Slab and Foundation Details Site Management Structural Protection Soil and Physical Barriers Surveillance and Remediation

81 Controlling Termites: Site Management Remove from site tree stumps all wood/cellulose containing debris Formwork (don t leave embedded in foundation) Soil Work Do not use excavation spoil under wood frame elements Drain water away from building (slope 5% for 10 ) Keep non-treated wood away from soil (6-8 code minimums)

82 Controlling Termites: Barrier/Foundations Physical Barriers 4 thick sand or crushed stone (1/16-1/10 Dia) beneath slab and/or along inside and outside of foundation wall Install sheet metal between top of foundation and sill plate Wrap perimeter foundation in mesh to protect at/below grade penetrations (1/32 grid spacing) Marine grade stainless steel mesh has 20yr service life Openings in slab/stem wall sealed with non-shrink grout Slabs and Foundations Slabs control joints and cracks don not exceed 1/25 Stem walls exposed for 8 above grade to allow inspection Keep crawl space access in floor instead of foundation walls

83 Controlling Termites: Details Brick Veneer Ground clearance: Brick Veneer Floor Joist Plate/sill 8 Foundation

84 Controlling Termites: Details Approx. 1

85 Controlling Termites: Details Wood Veneer Ground clearance: Wood veneer Floor Joist Plate/sill 8 6 Foundation

86 Controlling Termites: Details Approx 1-1/2

87 Controlling Termites: Details

88 Controlling Termites: Details Wood Veneer Concrete clearance: Wood veneer Floor Joist Plate/sill 6 Porch, walk, etc 2 Foundation

89 Controlling Termites: Details

90 Controlling Termites: Details Source: American Wood Council WCD 6

91 Controlling Termites: Details Floor joist Ground clearance: Crawl space Girder 8 Wood Post Moisture barrier

92 Controlling Termites: Details Ground clearance: Wood column 6 1 Wood Post Impervious Moisture Barrier Moisture barrier

93 Controlling Termites: Details Wood Post Ground clearance: Wood column 6 Moisture barrier

94 Controlling Termites: Details Source: American Wood Council WCD 6

95 Controlling Termites - Details Source: American Wood Council WCD 6

96 Controlling Termites - Details Source: American Wood Council WCD 6

97 Controlling Termites Structural Preservative Treated Wood CCA for interior damp, exterior above ground and exterior ground contact applications Borate treatments for interior dry and interior damp applications Termite Resistant species Yellow Cedar Cypress Redwood Western/Eastern Red Cedar

98 Outline Building Examples Potential Building Hazards Understanding Wood Moisture Control Durable Materials Controlling Termites Long Service Life

99 Service Life and Durability 47 Number of Buildings Age Class Years Source: Demolition Study Forintek Canada Corporation, Vancouver, B.C., Canada 2004

100 Service Life and Durability 60% Percent of Buildings 40% 20% Concrete Steel Wood 0% Age Class Years Source: Demolition Study Forintek Canada Corporation, Vancouver, B.C., Canada Source: Demolition Study Forintek Canada Corporation, Vancouver, B.C., Canada 2004

101 Service Life and Durability Percent of Buildings Age Class Years Source: Demolition Study Forintek Canada Corporation, Vancouver, B.C., Canada 2004

102 Service Life and Durability Demolition study (service life of buildings) Findings suggest no significant relationship between the structural system and the actual useful life of the building. Reasons for demolition: 1. Changing land value 2. Building does not meet current needs 3. Lack of maintenance of non-structural components Lessons: Determine realistic service life Resources: ISO 15686, CSA Find balance between building s intended use and adaptability Buildings designed for all purposes don t lend themselves to efficient/sustainable design

103 Service Life and Durability Fulton County Stadium, Atlanta, Georgia,

104 Questions? This concludes The American Institute of Architects Continuing Education Systems Course Wood Project Assistance WoodWorks Website

105 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. The Wood Products Council 2015