Building Construction Related to the Fire Service

1. Building Construction Related to the Fire Service

2. Learning Objective 1 Discuss the material properties of the wood products used in construction. Building Construction 7–1

3. Factors Affecting Wood Properties Wood is never dimensionally true Weather conditions can change size and shape Does not shrink or swell uniformly Defects Building Construction 7–2

4. Factors Affecting Wood Properties Strength varies Tensile strength Moisture content Lumber Building Construction 7–3

5. Solid Lumber Boards – Nominal thickness 2 inches (50 mm) or less Dimension lumber – Nominal thickness 2-4 inches (50 mm to 100 mm) or more Timbers – Nominal thickness 5 inches (125 mm) or more Actual dimensions of finished wood smaller than nominal dimension Building Construction 7–4

6. Laminated Wood Members Produced by joining flat strips of wood with glue Known as glulam beams Building Construction 7–5

7. Joints Used to Join Laminated Members Building Construction 7–6

8. Structural Composite Lumber Laminated veneer lumber Parallel strand lumber Laminated strand lumber Building Construction 7–7

9. Plywood Panels Building Construction 7–8

10. Nonveneered Panels Oriented stand board Particle board Wafer board Building Construction 7–9

11. Composite or Sandwich Panels Structural insulated panel (SIP) Building Construction 7–10

12. Span Rating of Panels Grading of wood panel products for structural use and exposure durability Panels stamped on back indicating intended application and suitability for exposure to water Building Construction 7–11

13. Span Rating of Panels Building Construction 7–12

14. Manufactured Components Prefabricated and shipped to construction site Trusses Light-frame Heavy-timber Building Construction 7–13

15. Manufactured Components Box beams and I-beams Building Construction 7–14

16. Learning Objective 2 Explain the variables that affect the combustibility of wood used as a construction material. Building Construction 7–15

17. Combustibility of Wood Structures Structural members provide large amount of fuel for combustion Voids in floor, roof, and wall cavities create combustible surface area surrounded by volumes of air for combustion Building Construction 7–16

18. Ignition Temperature Materials with lower ignition temperatures ignite easier Variables affecting ignition temperature Pyrolysis Building Construction 7–17

19. Heat of Combustion Total amount of thermal energy that could be released if fuel were completely burned Measured in BTUs/lb or kJ/kg Fire severity determined by several factors Release rate of energy determines fire growth rate and severity Building Construction 7–18

20. Surface Area and Mass Greater surface area for given mass permits more rapid combining of fuel vapors and air for combustion leading to overall greater rate of burning Surface-to-mass ratio Building Construction 7–19

21. Learning Objective 3 Describe the methods of treating wood with a fire retardant. Building Construction 7–20

22. Fire-Retardant Treatment of Wood Codes permit use of fire-retardant-treated wood for certain applications in fire-resistive and noncombustible construction Resists ignition Increases fire endurance NOT completely noncombustible Building Construction 7–21

23. Methods of Fire Retardant Treatment Surface coating Pressure impregnation Building Construction 7–22

24. Properties of Fire Retardants Most common are combinations of inorganic or organic salts Work by accelerating formation of charring in wood when wood is exposed to heat Intended to occur at temperatures lower than those developed in fires Building Construction 7–23

25. Disadvantages and Limitations of Fire Retardants Moisture Reduced strength of wood Stamping cannot be identified after placed in structure Building Construction 7–24

26. Thermoplastic Composite Lumber Produced from wood fiber and polyethylene or polyvinylchloride Not intended for use as structural framing Used for constructing outside decks and railings for its resistance to weathering Flame spread rating of 80 Building Construction 7–25

27. Learning Objective 4 Describe the framing systems constructed of wood and the purpose of fire stops in those framing systems. Building Construction 7–26

28. Heavy-Timber Framing Basic structural supported provided by framework of beams and columns with non-load-bearing walls Lower surface area-to-mass ratio, so greater structural endurance under fire conditions Building Construction 7–27

29. Heavy-Timber Framing Structural integrity in actual fire situation must be viewed conservatively Integrity affected by methods used to join joists, beams, and columns Design of connections must account for factors unique to wood Building Construction 7–28

30. Heavy-Timber Framing Connections must be able to transfer load from member to member Glulam beams used frequently for greater lengths Building Construction 7–29

31. Post and Beam Framing Beams less than heavy timber, but greater than light frame Creates square or rectangular shape that must be braced for diagonal stability Interior wood surface left exposed Exposed interior eliminates combustible voids Building Construction 7–30

32. Light Wood Framing Most popular Uses 2-inch (50 mm) nominal lumber Building Construction 7–31

33. Balloon Framing and Platform Framing Building Construction 7–32

34. Firestopping Required by codes to prevent rapid fire spread through concealed spaces within combustible construction Specific placement Draft stopping Building Construction 7–33

35. Learning Objective 5 Describe the materials used to construct the exterior and interior walls of a wood-frame building. Building Construction 7–34

36. Exterior Wall Materials Sheathing Building paper Insulation Combustible Noncombustible Siding material Building Construction 7–35

37. Brick Veneer Adds little structural support; adds insulation Protects wood frame from external exposure under fire conditions Very little fire behavior difference from wood frame Difficult to visually differentiate from brick Building Construction 7–36

38. Interior Finish Materials Interior walls can be left exposed, but most have an interior finish Most commonly used when degree of fire resistance is required Plaster Gypsum board Building Construction 7–37

39. Learning Objective 6 Discuss the considerations related to collapse, ignition-resistance, and deterioration as they relate to wood-frame construction. Building Construction 7–38

40. Collapse Once framing members exposed to fire, fairly rapid failure of structural system Fire can spread in four directions where truss joists used in floor construction Plywood or OSB subflooring with carpet or tile will fail within minutes Unfinished floor over basement space Building Construction 7–39

41. Ignition-Resistant Construction Decrease vulnerability of structures to exposure from wildland fires Codes for ignition-resistant construction Factors affecting hazard severity Ignition-resistant requirements Building Construction 7–40

42. Deterioration of Wood Buildings Causes unique to wood Insects Decay Shrinkage Causes common to other materials Settling Erosion Weathering Building Construction 7–41

43. Summary The distinguishing characteristic of a wood-frame building is the combustibility of the basic structural system. The structural integrity of the wood framing is lost as the wood is consumed, and structural failure will occur. Building Construction 7–42

44. Summary Wood-frame buildings, especially light wood, have numerous concealed spaces within walls, attics, and floor spaces that provide an avenue for fire spread. Concealed spaces contain building components that may lead to fires originating within the concealed spaces. Building Construction 7–43

45. Summary Fire-retardant treatments and wood products are continually changing so firefighters should stay current on the materials used in their response areas. Building Construction 7–44

46. Building Construction Review Questions 1. What are glulam beams? 2. How is pressure impregnation of wood performed? 3. What is the fire fighting advantage of post and beam framing? 7–45

47. Review Questions 4. What is platform framing? 5. When a degree of fire resistance is required, what are the most commonly used interior finish materials? Building Construction 7–46