1. Chapter 7 Wood-Frame Construction

2. Objectives
Understand and correctly use the terminology associated with wood construction.
Identify and describe six types of wood-frame structures classified as Type V construction.

3. Objectives
Identify and describe the specific fire protection differences between balloon-frame and platform-frame construction.
Describe the construction of a platform-frame building.

4. Objectives
Understand how a truss is constructed and how it performs from a fire protection perspective.
Explain the difference between firestopping and draftstopping.

5. Objectives
Describe the behavior of engineered and manufactured wood products under fire attack.
Describe the different types of sheathing, siding, and roofing materials.

6. Introduction Most fires are fought on, in, or under wood. Wood
Is combustible.
Construction creates a combustible void.
Can have a very rapid flame spread.

7. Definitions
Building terms are local in origin; different trades use different terms.
Wood-framed
Wall-bearing
Curtain walls
Wooden-walled building

8. Wood Frame Terminology
Chamfer
End matched
Engineered wood
Glued laminated timbers
Heavy timber
Joists
© Ms Deborah Waters/ShutterStock, Inc.

9. Wood Frame Terminology
Lumber
Matched lumber
Oriented strand board (OSB)
Plywood
Rough lumber
Splines and studs
Wood and wood lath
© DigitalVues/Alamy Images.

10. Uses of Wood in Buildings
Structural
Non-load-bearing
Roofing
Interior trim

11. Types of Wood-Frame Buildings
Log cabin
Post and frame
Balloon frame
Platform frame
Plank and beam
Truss frame

12. 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.
© Fanfo/ShutterStock, Inc.

13. 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.
Courtesy of Glenn Corbett.

14. Balloon Frame Wall of ordinary studs nailed together
Almost universal construction method for multistory wooden buildings until the middle of the 20th century
© Steve Holderfield/ShutterStock, Inc.

15. Fires in Balloon-Frame Buildings
Fire found in the walls can quickly cross the building through the joist channels.
Use of plumbing torch to braze a copper tube or thaw out a pipe can often be a culprit.

16. Fires in Balloon-Frame Buildings
Basement is usually the worst place for a fire to start.
Fire fighters need to anticipate the spread.
Extension sector
Vermiculite

17. Fires in Balloon-Frame Buildings
An illustration of a rundown, overcrowded, old Victorian balloon-frame house.

18. Platform Frame 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

19. Platform Frame
Inherent barriers to limit the spread of fire through the walls
Open stairwell
Soffits
Kitchen fire can extend through soffits.

20. Platform Frame
An illustration of a platform-framed house.

21. Constructing a Platform-Frame Building
Rough carpentry
Sill 
Subflooring 
Bridging
Header or bond course 
Trimmer

22. Constructing a Platform-Frame Building
Bottom plate 
Top plate 
Rafters 
Ridge boards
Hip 
Valley 
Stringers

23. Plank and Beam 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.

24. Plank and Beam
Fire in high open spaces can spread rapidly and develop into a huge volume.
Intermediate structures should be sprinklered or be of noncombustible construction.

25. Plank and Beam
A plank and beam building.

26. Lightweight Trusses and Other Wooden Members
Fire service has gradually developed knowledge of trusses.
Contribute to lighter-weight structures
Allow offsite prefabrication
Satisfy many building requirements

27. Lightweight Trusses and Other Wooden Members
Lighter in weight than solid construction
Provide long, clear spans
Can be delivered prefabricated
© Renata Sedmakova/ShutterStock, Inc.

28. Lightweight Wood Trusses
In use since 1960s
Steel gusset plates (gang nails)
Courtesy of Glenn Corbett.

29. Lightweight Wood Trusses
Finger joints are used to create a longer piece of dimensional lumber.
Courtesy of American Wood Council, Leesburg, VA.

30. Dangers of Wood Truss Floors
Are a hazard to fire fighters
High surface-to-mass ratio
Heating of the gusset plate will decompose tensioned wood fibers.
No outward indication of truss building presence
May be disclosed by smoke or fire pushing through the wall at the floor line

31. Dangers of Lightweight Wood Truss Roofs
Equally hazardous as wood truss floors
Lack a ridge pole
Exposed roofs can fall
Ventilation
Roof collapse during a fire
© Portlandia/ShutterStock, Inc.

32. Truss Void
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.

33. Truss Void
The National Fire Protection Association (NFPA) Fire Protection Handbook
Concentration (in parts per million [ppm]) × duration (minutes) = 33,000 is likely to be dangerous.
The flammability range of carbon monoxide is from 12.5% to 74%.

34. Catastrophe Potential
Lateral extension of truss
Support a balcony that is the only exit for occupants

35. Catastrophe Potential
Firestopping is penetrated by lighting circuits.
Stairway exit can be involved in fire and collapse before the occupants have escaped.
Exit facilities should be totally separated from the truss void.

36. Automatic Sprinklers and Truss Voids
NFPA 13R
Intended to prevent flashover and save lives
Code describes partial systems that should not be expected to provide full fire suppression.

37. Lightweight Wooden I-Beams
Wooden beam
Sawn beam
Steel I-beam
Sawn wooden beam
Wooden I-beams
Web of the I-beam

38. Truss Frame
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.

39. Truss Frame
Loss of a stud could precipitate collapse of the integral roof or floor truss.
Design assumes that every truss member will remain in its assigned position under load.

40. Firestopping and Draftstopping
Fire spreads through hidden voids.
No tested standards for wood firestopping or draftstopping

41. Differences: Firestopping and Draftstopping
Both limit the spread of fire.
Firestops typically limit vertical movement.
Draftstops limit horizontal movement.

42. Types of Firestopping
Inherent firestopping results from normal building construction.
Legal firestopping meets the requirements of a code.

43. Effectiveness of Firestopping
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.

44. Effectiveness of Firestopping
Not all building inspectors are familiar with the basic gas law:
If the temperature rises and the volume remains the same, the pressure rises.

45. Cutoff Ends of Joists Used as firestopping
No seal because the wood “cut out” creates a space

46. West and East Coasts Uniformly unsatisfactory practices
Sheet of gypsum board “buttered” into place
Thin plywood or flake board poorly fitted

47. 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

48. 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.

49. 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.

50. Impregnation Wood can be impregnated in a variety of ways.
Pressure or chemically treated
Wood cannot be made fireproof or noncombustible.
It can be made fire retardant.

51. 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.

52. Underwriters Laboratories, Inc. (UL)
Provides various classifications of treated lumber
Consult “Lumber, Treated (BPW).”

53. Chemicals
Previously used ones impregnated the wood but leached out and corroded metal connectors.
New products cite noncorrosive materials.

54. 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.

55. Surface Coatings Intumescent coatings swell up when heated.
People spread it thinner than recommended.
Applying to existing installations leaves the unexposed surface untreated.

56. Dangerous Treated Wood
Treated plywood and lumber have been used for basement walls.
Widely used for exterior structures
Still combustible and might cause a collapse
Fumes are toxic.

57. 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.

58. Spliced Timbers Are joined by metal connectors to transfer loads
The spliced timber acts as a single member.
Heated metal connections can destroy the wood and the timber may fail.

59. Laminated Timbers
Plank-like sections of nominal 2-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.

60. 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.

61. Planks
Fabricated by gluing three boards together with the center board protruding on one side and indented on the other
May separate during fire, causing boards to fall from the overhead.

62. Chipboard Wood chips are often glued together to make flat sheets.
Sometimes used for the floors of mobile homes
Some is water soluble.

63. 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.

64. Sheathing Covering applied to the studs or framing of a structure
Exterior surface covers the sheathing.
Many old houses were built without sheathing.

65. Low-Density Black Fiberboard
Moisture and vermin proof
Carries the warning, “Combustible. May burn or smolder if ignited”
Plumber’s torch

66. 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.

67. Foamed Plastic Also used for sheathing
May or may not be flame-inhibited
In a fire, may degrade and give off noxious fumes

68. Siding Novelty siding Batten Plywood siding Shingle and shake
Asbestos cement shingle 
Asphalt felt siding
Courtesy of Glenn Corbett.

69. Siding Vinyl siding Metal siding Corrugated metal siding Stucco
Courtesy of Glenn Corbett.

70. 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.

71. Stone Veneer Natural or artificial stone and cast concrete
Permastone is one trade name.
Courtesy of Glenn Corbett.

72. Wood Shingle Roofing 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.

73. Wood Shingle Roofing A strong comeback
Many areas have wood-shingled roofs.
Permitted wherever frame buildings are permitted
© Design Pics/Thinkstock.

74. 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.

75. Tile Roofs Heavy tile roof Collapse of thousands of pounds of tile
Truss-supported tile failure
Courtesy of Glenn Corbett.

76. 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

77. 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.

78. Summary Type V construction has six types of wood-frame structures.
In a balloon-frame building, fire can spread from cellar to attic and across the ceiling.
The current practice of designing buildings of lighter and lighter materials and substituting geometry for mass has brought about significant strides in the architectural field.

79. Summary
One major problems of combustible construction is fire spread through hidden voids.
Firestopping is often required by code to be installed to prevent the spread of fire.
Wood cannot be made either fireproof or noncombustible.
Combustibility can be dealt with only by complete automatic sprinkler protection.