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Ch 06 Wood Frame Construction
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Ch 06 Wood Frame Construction

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  • Courtesy of APA- The Engineered Wood Association
  • © DigitalVues/Alamy Images
  • © Steve Holderfield/ShutterStock, Inc.
  • Photo courtesy of Blaze-tech Fire Protection
  • Courtesy of the estate of Francis L. Brannigan
  • Transcript

    • 1. 6 Wood Frame Construction
    • 2. Objectives (1 of 3)
      • Identify and describe six types of wood frame structures classified as Type V construction
      • Identify and describe the specific fire protection differences between balloon frame and platform frame
      6
    • 3. Objectives (2 of 3)
      • Describe the construction of a platform-frame building
      • Understand how a truss is constructed and how it performs from a fire protection perspective
      • Explain the difference between firestopping and draftstopping
      6
    • 4. Objectives (3 of 3)
      • Describe the behavior of engineered and manufactured wood products under fire attack
      • Describe the different types of wood siding and roofing materials
      6
    • 5. Introduction
      • Most fires are fought on, in, or under wood.
      • Basic facts about wood
        • It is combustible
        • It creates combustible void spaces in which fire can hide and burst out
        • It can, in thin sections, have a very rapid flame spread
      6
    • 6. Definitions
      • Building terms are local in origin; different trades use different terms
        • Wood-framed
        • Wall-bearing
        • Curtain walls
        • Wooden-walled building
      6
    • 7. Wood Frame Terminology (1 of 2)
      • Chamfer
      • End matched
      • Engineered wood
      • Glued laminated timbers
      • Heavy timber
      • Joists
      6
    • 8. Wood Frame Terminology (2 of 2)
      • Lumber
      • Matched lumber
      • Oriented strand board (OSB)
      • Plywood
      • Rough lumber
      • Splines and studs
      • Wood and wood lath
      6
    • 9. Uses of Wood in Buildings
      • Structural
      • Non-load-bearing
      • Roofing
      • Interior trim
      6
    • 10. Types of Wood-Frame Buildings
      • Log cabin
      • Post and frame
      • Balloon frame
      • Platform frame
      • Plank and beam
      • Truss frame
      6
    • 11. Log Cabin
      • Constructed of entire tree trunks
      • Many older buildings, even multistory buildings, are concealed log cabins
      • Many carry unexpectedly heavy loads
      • Interior surfaces of log cabins might be boards or plywood
      6
    • 12. Post and Frame
      • Has an identifiable frame or skeleton of timber fitted together
      • Mortise and tenon
      • Trunnels
      • The walls are not structural or load-bearing.
      6
    • 13. Balloon Frame
      • Wall of ordinary studs nailed together
      • Almost universal construction method for multi-story wooden buildings until the middle of the 20 th century
      6
    • 14. Fires in Balloon-Frame Buildings (1 of 2)
      • Fire can spread through all the interconnected spaces
      • Interconnected voids are one big balloon
      • Installing firestopping in an old building is costly
      6
    • 15. Fires in Balloon-Frame Buildings (2 of 2)
      • Basement is usually the worst place for a fire to start
      • Fire fighters need to anticipate the spread.
      • Extension sector
      • Vermiculite
      6
    • 16. Platform Frame (1 of 2)
      • The first floor is built as a platform
      • Subflooring is laid on the joists
      • Frame for the first-floor walls is erected on the first floor
      • No continuity from top to bottom
      6
    • 17. Platform Frame (2 of 2)
      • Inherent barriers to limit the spread of fire through the walls
      • Open stairwell
      • Soffits
      • Kitchen fire can extend through soffits
      6
    • 18. Constructing a Platform-Frame Building (1 of 2)
      • Rough carpentry
      • Sill 
      • Subflooring 
      • Header or bond course 
      • Trimmer
      6
    • 19. Constructing a Platform-Frame Building (2 of 2)
      • Bottom plate 
      • Top plate 
      • Rafters 
      • Ridge boards
      • Hip 
      • Valley 
      6
    • 20. Plank and Beam (1 of 2)
      • Built with heavier beams
      • Thick, finished tongue and groove planks are used for flooring
      • Reduces the volume of concealed space
      • Interior finishes have high flame spread and smoke-developing characteristics
      6
    • 21. Plank and Beam (2 of 2)
      • Fire in high open spaces can spread rapidly and develop into a huge volume
      • Intermediate structures should be sprinklered or be of noncombustible construction
      6
    • 22. Lightweight Trusses and Other Wooden Members (1 of 2)
      • Fire service has gradually developed knowledge of trusses
      • Contribute to lighter-weight structures
      • Allow offsite prefabrication
      • Satisfy many building requirements
      6
    • 23. Lightweight Trusses and Other Wooden Members (2 of 2)
      • Lighter in weight than solid construction
      • Provides long clear spans
      • Can be delivered prefabricated
      6
    • 24. What Is a Truss?
      • A framed structure consisting of a triangle or group of triangles arranged in a single plane
      • Loads applied at intersections of the members will cause direct stresses in the members
      • Loads applied between these points cause flexural stresses
      6
    • 25. Rigidity (1 of 2)
      • Geometric principle
      • Triangle is inherently stable
      • Economy
      • Chords
      6
    • 26. Rigidity (2 of 2)
      • Struts
      • Ties
      • Panel points
      • Web
      6
    • 27. Principle Types (1 of 2)
      • Parallel-Chord Truss
        • The bottom and top chords are parallel.
        • Steel bar joist
        • Long-span parallel-chord roof trusses have a slight upward pitch to the center.
        • Are being used for floors and roofs
      6
    • 28. Principle Types (2 of 2)
      • Triangular Trusses
        • Triangular in shape in order to provide a peaked roof
        • Must be closely spaced
      6
    • 29. Connectors
      • A problem in truss design
      • Connectors now capable of transmitting heavy loads
      6
    • 30. Compression vs. Tension (1 of 2)
      • Normal truss:
        • Top chord in compression and bottom chord in tension
      6
    • 31. Compression vs. Tension (2 of 2)
      • Cantilever is reversed:
        • Top chord in tension and bottom chord in compression
      • In sketches, compression members are often shown as thick lines, while tension members are shown as thin lines
      6
    • 32. Truss Principles, Case #1
      • A building span of 20 feet
      • Two 10-foot ­I-beams extend from the walls.
      • Assume each beam can carry 1000 pounds.
      • If column is removed, beam would have to be 20 feet long but carry only 500 pounds
      6
    • 33. Truss Principles, Case #2 (1 of 2)
      • The column is cut off and a stub remains at the junction of the beams
      • A triangle restores the load­carrying capacity of the beam
      6
    • 34. Truss Principles, Case #2 (2 of 2)
      • A truss with single compression member extending downwards is called an inverted king post truss
      • A truss with two compression members is called a queen post truss
      6
    • 35. Problems with Trusses
      • Failure
      • Multiple truss failures
      • Rising roofs
      • Tables of allowable design stresses
      • Defective design
      • Competition in the supply business
      6
    • 36. Truss Failure in Fires
      • Economy of the truss
      • Bottom chord: under compression
      • Top chord: in tension
      • Compressive load
      • Ties
      • Large triangular trusses
      6
    • 37. Wood Truss Floors
      • Are a hazard to fire fighters
      • Heating of the gusset plate will decompose tensioned wood fibers
      • No outward indication of their presence
      • May be disclosed by smoke or fire pushing through the wall at the floor line
      6
    • 38. Truss Void (1 of 2)
      • Found within a truss roof system, this void space is between the top floor ceiling and the roof
      • Represents a large area in which explosive carbon monoxide can accumulate
      • Voids are interconnected horizontally and vertically
      6
    • 39. Truss Void (2 of 2)
      • The National Fire Protection Association (NFPA) Fire Protection Handbook
      • Concentration (in parts per million [ppm]) x duration (minutes) = 35,000 is likely to be dangerous
      • The flammability range of carbon monoxide is from 12.5 to 74 percent
      6
    • 40. Catastrophe Potential (1 of 2)
      • Lateral extension of truss
        • May support a balcony that is the only exit for occupants
      6
    • 41. Catastrophe Potential (2 of 2)
      • Truss passes through outside wall
        • Only firestopping is typically gypsum “buttered” in place with cement
        • Firestopping is penetrated by lighting circuits
      • Stairway exits with truss voids
        • If involved in fire, can collapse before the occupants have escaped
      6
    • 42. Automatic Sprinklers and Truss Voids
      • NFPA 13R
        • Purpose to prevent flashover and save lives
        • Code describes partial systems that should not be expected to provide full fire suppression
      6
    • 43. Lightweight Wooden I-Beams
      • Wooden beam
      • Sawn beam
      • Steel I-beam
      • Sawn wooden beam
      • Wooden I-beams
      • Web of the I-beam
      6
    • 44. Truss Frame (1 of 2)
      • The roof and floor trusses and studs are tied into a unitized frame
      • The small dimension lumber will burn faster than larger solid lumber
      • Unsupported spans in trussed structures are subject to total collapse
      6
    • 45. Truss Frame (2 of 2)
      • Loss of a stud could precipitate the collapse of the integral roof or floor truss
      • Design assumes that every truss member will remain in its assigned position under load
      6
    • 46. Firestopping
      • Fire spreads through hidden voids
      • No tested standards for wood firestopping or draftstopping
      6
    • 47. Differences: Firestopping and Draftstopping
      • Both limit the spread of fire
      • Firestops typically limit vertical movement
      • Draftstops limit horizontal movement
      6
    • 48. Types of Firestopping
      • Inherent firestopping results from normal building construction
      • Legal firestopping meets the requirements of a code
      6
    • 49. Effectiveness of Firestopping (1 of 2)
      • The lack of firestopping in one stud channel is sufficient to transmit fire
      • In older houses, sides of the chimney-like stud channels are combustible
      • Lack of firestopping is particularly critical in balloon-frame buildings
      6
    • 50. Effectiveness of Firestopping (2 of 2)
      • Not all building inspectors are familiar with the basic gas law:
        • If the temperature rises and the volume remains the same, the pressure rises
      6
    • 51. Cutoff Ends of Joists
      • Used as firestopping
      • No seal because the wood “cut out” creates a space
      6
    • 52. West and East Coasts
      • Uniformly unsatisfactory practices
      • Sheet of gypsum board “buttered” into place
      • Thin plywood or flake board poorly fitted
      6
    • 53. Removal of Firestops
      • Removed for the installation of such items as heat ducts, electrical cables, sprinkler systems, and central vacuum cleaner systems
      • Unlikely to be replaced
      6
    • 54. Draftstopping and Truss Floors
      • Truss voids in each floor
      • Truss proponents argue that firestopping will mitigate the problem
      • Severe backdraft explosion can provide a significant collapse
      6
    • 55. Protecting Wood from Ignition
      • Sobering News
        • Most fires are fought by fire fighters standing on, in, or under a combustible structure
        • Encasing wood in concrete promotes decay
      6
    • 56. Impregnation
      • Wood can be impregnated in a variety of way: pressure- or chemically-treated.
      • Wood cannot be made fireproof or noncombustible
      • It can be made fire retardant
      • Impregnated wood is not noncombustible wood
      6
    • 57. Pressure Treatment
      • Can reduce wood’s flame spread
      • Pressure treatment can reduce the hazard of wood construction
      • Treated wood will burn, although at a slower rate
      6
    • 58. Underwriters Laboratories, Inc. (UL)
      • Provides various classifications of treated lumber
      • Consult “Lumber, Treated (BPW)”
      6
    • 59. Chemicals
      • Previously used ones impregnated the wood but leached out and corroded metal connectors
      • New products cite noncorrosive materials
      6
    • 60. Bad Practices
      • Fire retardant plywood (FRT), one sheet wide, on both sides of a firewall
      • Plywood delaminates with fire exposure
      • Plywood treated with certain chemicals decays from heat
      6
    • 61. Surface Coatings
      • Intumescent coatings swell up when heated
      • People spread it thinner than recommended
      • Applying to existing installations leaves the unexposed surface untreated
      6
    • 62. Dangerous Treated Wood
      • Pressure treated plywood and lumber treated has been used for basement walls
      • Widely used for exterior structures
      • Still combustible and might cause a collapse
      • Fumes are toxic
      6
    • 63. Plywood
      • Plywood was seen as answer to wood’s lack of shear strength
      • Plywood exposed to fire delaminates
      • Plywood can be impregnated to render it fire retardant
      6
    • 64. Spliced Timbers
      • Are joined by metal connectors to transfer loads
      • Acts as a single member
      • Heated metal connections can destroy the wood and the timber may fail
      6
    • 65. Laminated Timbers
      • Plank-like sections of nominal two-inch boards are glued under pressure
      • Burn like solid heavy timbers and do not delaminate like plywood
      • Laminated wooden beams are not the same thing as wooden I-beams
      6
    • 66. Paper Wrapping
      • Laminated timbers are shipped in a protective paper wrapper
      • Paper is hemp-reinforced and coated with a bituminous moisture repellant
      • Paper ignites readily and has a high flame spread
      6
    • 67. Planks
      • Fabricated by gluing three boards together with the center board protruding on one side and indented on the other
      • A sample ignited burned like a solid piece of wood
      6
    • 68. Finger Joints
      • Made by cutting a series of long points into the end of each piece
      • The joints are glued together
      6
    • 69. Chipboard
      • Wood chips are often glued together to make flat sheets
      • Sometimes used for the floors of mobile homes
      • Some is water soluble
      6
    • 70. Flitch Plate Girders
      • A composite of a steel plate or plywood sandwiched between two beams
      • Failure of the connection between the wood and steel could cause failure
      6
    • 71. Wood and Plastic Roof Panels
      • Large plywood roof panels with a gypsum board interior surface sandwiched a thick plastic foam core to create panels
      • Panel used as a roof support
      • Dangerous to vent such a roof
      6
    • 72. Sheathing
      • Covering applied to the studs or framing of a structure
      • Exterior surface covers the sheathing.
      • Many old houses were built without sheathing
      6
    • 73. Low-Density Black Fiberboard
      • Moisture and vermin proof
      • Carries the warning, “Combustible. May burn or smolder if ignited.”
      • Plumber’s torch
      6
    • 74. Plywood and Gypsum
      • Both are used for sheathing
      • Combined with brick veneer surfacing and gypsum interior surface, gypsum is used to provide rated fire-resistive exterior walls
      6
    • 75. Foamed Plastic
      • Also used for sheathing
      • May or may not be flame-inhibited
      • In a fire, may degrade and give off noxious fumes
      6
    • 76. Siding (1 of 2)
      • Novelty siding 
      • Batten 
      • Plywood siding 
      • Shingle and shake 
      • Asbestos cement shingle 
      6
    • 77. Siding (2 of 2)
      • Asphalt felt siding
      • Vinyl siding 
      • Metal siding 
      • Corrugated metal siding 
      • Stucco 
      6
    • 78. Brick Veneer
      • Is laid up from the foundation in one wythe
      • Such a wall is unstable because it is thin
      • Galvanized steel anchors are nailed to the studs
      • Pyrolytic decomposition can be an issue
      6
    • 79. Stone Veneer
      • Natural or artificial stone and cast concrete
      • Permastone is one trade name
      6
    • 80. Wood Shingle Roofing (1 of 2)
      • Fire hazard
        • Some of the greatest fire disasters in history have been due to the spread of fire by wood shingle roofs
        • The conflagration hazard presented by wood shingles is a serious consideration
      6
    • 81. Wood Shingle Roofing (2 of 2)
      • A Strong Comeback
        • Many areas have wood-shingled roofs.
        • Permitted wherever frame buildings are permitted
      6
    • 82. Testing Laboratories
      • Rate wood shingles in accordance to NFPA 256
      • Elements considered include flame exposure, spread of flame, and resistance to burning
      • Roofing materials are classified as A, B, or C
      6
    • 83. Tile Roofs
      • Heavy tile roof
        • Collapse of thousands of pounds of tile
        • Truss-supported tile failure
      6
    • 84. Imitation Timber
      • Watch for the following:
        • Unprotected steel beams or columns boxed in wood
        • Unprotected steel encased in plaster
        • False wood beams
        • Polyurethane imitation wood beams
      6
    • 85. Making Wood Construction Safe
      • Wood is a uniquely renewable resource
      • Unfortunately it is combustible
      • Combustibility can be dealt with only by complete automatic sprinkler protection
      6
    • 86. Summary (1 of 2)
      • Type V construction has six types of wood frame structures
      • In a balloon-frame building, fire can spread through all the interconnected spaces from cellar to attic and across the ceiling
      • Firestopping is often required by code to be installed to prevent the spread of fire
      6
    • 87. Summary (2 of 2)
      • Trusses and specially treated or constructed wood materials create unique challenges for fire protection
      • Wood cannot be made fireproof or noncombustible
      • Combustibility can be dealt with only by complete automatic sprinkler protection
      6