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

Ch 06 Wood Frame Construction Ch 06 Wood Frame Construction Presentation Transcript

  • 6 Wood Frame Construction
  • 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
  • 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
  • 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
  • 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
  • Definitions
    • Building terms are local in origin; different trades use different terms
      • Wood-framed
      • Wall-bearing
      • Curtain walls
      • Wooden-walled building
  • Wood Frame Terminology (1 of 2)
    • Chamfer
    • End matched
    • Engineered wood
    • Glued laminated timbers
    • Heavy timber
    • Joists
  • Wood Frame Terminology (2 of 2)
    • Lumber
    • Matched lumber
    • Oriented strand board (OSB)
    • Plywood
    • Rough lumber
    • Splines and studs
    • Wood and wood lath
  • Uses of Wood in Buildings
    • Structural
    • Non-load-bearing
    • Roofing
    • Interior trim
  • Types of Wood-Frame Buildings
    • Log cabin
    • Post and frame
    • Balloon frame
    • Platform frame
    • Plank and beam
    • Truss frame
  • 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
  • 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.
  • 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
  • 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
  • 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
  • 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
  • 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
  • Constructing a Platform-Frame Building (1 of 2)
    • Rough carpentry
    • Sill 
    • Subflooring 
    • Header or bond course 
    • Trimmer
  • Constructing a Platform-Frame Building (2 of 2)
    • Bottom plate 
    • Top plate 
    • Rafters 
    • Ridge boards
    • Hip 
    • Valley 
  • 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
  • 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
  • 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
  • Lightweight Trusses and Other Wooden Members (2 of 2)
    • Lighter in weight than solid construction
    • Provides long clear spans
    • Can be delivered prefabricated
  • 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
  • Rigidity (1 of 2)
    • Geometric principle
    • Triangle is inherently stable
    • Economy
    • Chords
  • Rigidity (2 of 2)
    • Struts
    • Ties
    • Panel points
    • Web
  • 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
  • Principle Types (2 of 2)
    • Triangular Trusses
      • Triangular in shape in order to provide a peaked roof
      • Must be closely spaced
  • Connectors
    • A problem in truss design
    • Connectors now capable of transmitting heavy loads
  • Compression vs. Tension (1 of 2)
    • Normal truss:
      • Top chord in compression and bottom chord in tension
  • 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
  • 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
  • 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
  • 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
  • Problems with Trusses
    • Failure
    • Multiple truss failures
    • Rising roofs
    • Tables of allowable design stresses
    • Defective design
    • Competition in the supply business
  • Truss Failure in Fires
    • Economy of the truss
    • Bottom chord: under compression
    • Top chord: in tension
    • Compressive load
    • Ties
    • Large triangular trusses
  • 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
  • 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
  • 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
  • Catastrophe Potential (1 of 2)
    • Lateral extension of truss
      • May support a balcony that is the only exit for occupants
  • 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
  • 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
  • Lightweight Wooden I-Beams
    • Wooden beam
    • Sawn beam
    • Steel I-beam
    • Sawn wooden beam
    • Wooden I-beams
    • Web of the I-beam
  • 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
  • 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
  • Firestopping
    • Fire spreads through hidden voids
    • No tested standards for wood firestopping or draftstopping
  • Differences: Firestopping and Draftstopping
    • Both limit the spread of fire
    • Firestops typically limit vertical movement
    • Draftstops limit horizontal movement
  • Types of Firestopping
    • Inherent firestopping results from normal building construction
    • Legal firestopping meets the requirements of a code
  • 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
  • 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
  • Cutoff Ends of Joists
    • Used as firestopping
    • No seal because the wood “cut out” creates a space
  • West and East Coasts
    • Uniformly unsatisfactory practices
    • Sheet of gypsum board “buttered” into place
    • Thin plywood or flake board poorly fitted
  • 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
  • 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
  • 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
  • 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
  • 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
  • Underwriters Laboratories, Inc. (UL)
    • Provides various classifications of treated lumber
    • Consult “Lumber, Treated (BPW)”
  • Chemicals
    • Previously used ones impregnated the wood but leached out and corroded metal connectors
    • New products cite noncorrosive materials
  • 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
  • Surface Coatings
    • Intumescent coatings swell up when heated
    • People spread it thinner than recommended
    • Applying to existing installations leaves the unexposed surface untreated
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • Finger Joints
    • Made by cutting a series of long points into the end of each piece
    • The joints are glued together
  • Chipboard
    • Wood chips are often glued together to make flat sheets
    • Sometimes used for the floors of mobile homes
    • Some is water soluble
  • 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
  • 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
  • Sheathing
    • Covering applied to the studs or framing of a structure
    • Exterior surface covers the sheathing.
    • Many old houses were built without sheathing
  • Low-Density Black Fiberboard
    • Moisture and vermin proof
    • Carries the warning, “Combustible. May burn or smolder if ignited.”
    • Plumber’s torch
  • 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
  • Foamed Plastic
    • Also used for sheathing
    • May or may not be flame-inhibited
    • In a fire, may degrade and give off noxious fumes
  • Siding (1 of 2)
    • Novelty siding 
    • Batten 
    • Plywood siding 
    • Shingle and shake 
    • Asbestos cement shingle 
  • Siding (2 of 2)
    • Asphalt felt siding
    • Vinyl siding 
    • Metal siding 
    • Corrugated metal siding 
    • Stucco 
  • 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
  • Stone Veneer
    • Natural or artificial stone and cast concrete
    • Permastone is one trade name
  • 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
  • Wood Shingle Roofing (2 of 2)
    • A Strong Comeback
      • Many areas have wood-shingled roofs.
      • Permitted wherever frame buildings are permitted
  • 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
  • Tile Roofs
    • Heavy tile roof
      • Collapse of thousands of pounds of tile
      • Truss-supported tile failure
  • 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
  • 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
  • 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
  • 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