Chapter 3 Building construction

Two major codes

NFPA 5000 Building Construction and safety code councils (ICC), International Building Code (IBC)

Five Types

1. Fire-resistive construction, provides highest level of protection from fire spread.

2. Non-combustible construction, composed of material that won’t contribute to spread or fire development.

3. Ordinary construction, commonly found in mercantile, business, and residential structures, older schools.

4. Heavy timber, characterized by the use of large-dimensional lumber/laminated wood.

5. Wood frame, the exterior load-bearing walls are composed entirely of wood.

Type 1 Construction (Fire-Resistive)

Composed of noncombustible or limited combustible materials with high fire-resistive rating to not add fuel to load, considered collapse resistant.

Incorrectly referred to FIREPROOF

Conditions

• Compartments can retain heat, contributing to the potential for rapid fire development.

• Rods may be extremely difficult to penetrate for ventilation purposes due to construction material and designs.

• Windows may be non-operating, causing them to be very difficult to open for ventilation.

Type 2 Construction (noncombustible)

Do not meet same strict requirements as Type 1 but still do not add fuel load.

Most common form includes

• metal framing members

• metal cladding

• concrete-block wall

• unprotected, open web joists supporting metal roof decks

More prone to collapse than type 1 because lighter-weight materials with lower fire-resistance ratings

Type 3 Construction (Ordinary Construction)

Exterior walls/structural members

• constructed of noncombustible/limited combustible materials.

Interior walls

Completely or partially constructed of wood

• Walls

• Columns

• Beams

• Floors

• Roofs

Fire behavior influences

• Void spaces inside wooden channels that roof and truss systems create between wall studs are less protected than Type 1 & 2. Fire spread through voids unless fire stops installed

• Prefabricated wood truss systems similar to those in Type 5 may be in NEW Type 3 structures. May fail fast when exposed to fire.

Type 4 Construction (Heavy Timber)

Vary of building code in use at time of construction.

Dimension of structure

Must adhere to minimum dimension sizing

• Columns

• Beams

• Joists

• Girders

Extremely stable/resistant to collapse due to sheer mass of structural members.

Exterior walls are noncombustible

Interior elements

• Floors, Walls, Roofs

• Constructed of solid or laminated wood, no concealed spaces.

Modern Type 4 may include small-dimensioned lumber glued together to form laminated structural element (glue-laminated/glulam elements)

Glue-laminated beams may fail when exposed to fire because heat affects the glue.

Fire behavior influences

• High concentration of wood can contribute to the intensity of fire once it starts

• Collapse of masonry walls can be caused by loss of structural integrity of timbers

Type 5 Construction (Wood Frame)

Veneer of stucco, brick, stone constructed over wood framing. Appear like Type 3 but provide little protection/structural support.

Examples

• Single-family residences

• Multistory apartment buildings

Type 5 consists of

• wood 2 × 4 or 2 × 6-inch studs

• Exterior covered with siding spread or help fire spread

• Nails, screws, glue attach siding

• Stucco spread of screen lattice and attached to framing studs

• Vinyl (petroleum-based fuel)

• Produces dense, dark, oily toxic smoke that melts away

• Insulation/sheathing exposed after fire melts siding are combustible and add fuel to fire

• Some include 6-inch exterior wall cavities for increase insulation, some use exterior insulation.

• Prefabricated wood truss system in place of solid floor joists (create large open voids)

• Wood I-beams (central piece of thin plywood/composite, glued to two 2 × 4-inch pieces forming top and bottom of the truss.) May have holes for plumbing, electrical, etc.

• Adhesives are no more or less reliable than other construction methods.

• Size-up, duration of fire, fireground actions at scene are more important indicators of collapse than construction methods used

Factory-Built Homes

Known as Manufactured, Prefabricated Modular Industrialized housing.

Manufactured (Mobile) Homes

• Wheels/Permanent steel undercarriage for towing

• One-section single wide to Three-section triple-wide homes

• Not required to conform to model building codes

• Conform to U.S. Department of Housing and Urban Development (HUD) standard similar to Type 5.

• HUD code based on performance standards and tends to encourage construction innovations

• Fire-resistance vary on age

• Before 1976 have less fire resistance

• Anchored to concrete slabs or have crawl spaces beneath them (additional source of O2 during fire)

• Fire spread fast because small walls, ventilation-limited fast as result. (Adequate ventilation cause fire spread faster)

• NFPA analysis of fire spread show DECLINE in manufactured homes since 1980

Reductions in Fire Loss/Fatalities

• Smoke/carbon monoxide alarms

• Flame-retardant materials in interior finishes

• Flame-retardant materials around heating/cooking equipment

• Safer heating/cooking equipment

• Gypsum board rather than wood paneling in interior finishes

• Fire suppression systems (sprinklers)

Other Types of Factory-Built Homes

Factory-based homes referred to

• Modular Homes - sectional homes comply with same local building codes as site-built homes, only 6% of all factory-built homes are modular

  • Can be stacked vertically/connected horizontally

  • Sections transported to site, attached to permanent foundation (maybe basement)

• Panelized Homes - assembled on-site from pre-constructed panels of foam insulation sandwiched between sheets of plywood. Panels 8 feet wide by 40 feet long.

  • Bottom edges of wall panels are recessed to fit over foundation

  • Each has wiring chases

  • Panels self-supporting, framing unnecessary

• Pre-cut Homes - individual parts custom cut, assembled on-site, variety styles

  • Pole houses

  • Post-and-beam construction

  • Log homes

  • A-frames

  • Geodesic dome

• Hybrid modular structure - most recent made factory-built homes, include elements of modular and panelized design. Modular core for bathrooms, mechanical rooms made in factory. Panels then added to modules complete build.

Floor, Ceilings, Walls

Floors & Ceilings

• Floor on ground is concrete/joist and deck for crawl space/basement

• Upper floors are joists and decking with ceiling attached to bottom

• Top level is ceiling, joist/rafters, roof

• Space between floor/ceiling or ceiling/roof

  • Duct work/open return air plenum

  • Electrical/Communications wiring

  • Water/Natural gas pipes

  • Pipes for fire suppression system

  • Recessed lights/audio system

  • Fiberglass, cellulose, foam insulation under roof/floors as sound proofing

• Floor/Ceiling construction

  • Poured reinforced concrete

  • Cellular concrete over metal decking

  • Finished wood, tile, carpet over wood subfloor attached to metal/wood joists

  • Ceilings generally

    • Gypsum board

    • Tin tiles

    • Lath & plaster attached to joist, roof trusses, beams

Walls

• Exterior wall maybe wood/metal siding attached to

  • Studs

  • Single layer of concrete

  • Concrete blocks

  • Logs

• Walls layout (bottom/top plate, vertical studs, horizontal braces, between two gypsum boards or lath/plaster)

• Cavity makes void spaces or filled with insulation

• Fire walls meet specified fire-resistance rating

• Fire wall layout include wall, window, door, other protected opening meeting required protection opening

• Fire wall for adjoining buildings/2 occupancy classifications

• Owners/Contractors penetrate walls for (pipes, wires, ducts) reduce/eliminate fire wall protection

Basement & Stairs

Basement

• Basement partially/fully below grade level, limited ingress/egress, limited ventilation

• Walk-out/daylight built on slope (one or more have door/windows)

• Some have exterior/interior stairs

• Maybe unfinished no drywall

• Exposed studs/joists less resistance making structure part of fuel load (if members fail, will collapse)

Stairs

• Means of egress stairs are protected/enclosed

• not requires as egress are access/convenience

• Fire escapes, escalators, fixed ladders egress in past they no longer allowed as egress

• Protected stairs - enclosed fire-rated construction with 1–2-hour rating based on building height

• Protected stairs normally serve two or more stories, required means of egress

• Control doors on protected stairs for integrity of stairwell

• Door allows for vent control and evacuation

• Secure door in open position to not endanger victim/firefighter

• High-rise may have pressurized system that fail if doors left open

Exterior Stairs

• Maybe open to air or enclosed

• Enclosed comply with requirements similar to interior stairs

• Open stairs ventilated but closed to weather

• Two adjacent sides open to ventilation

Unprotected Stairs

• Not enclosed with fire-rated construction, act as flow path for fire/smoke

• No protection from exposure

• Codes allow stair when only connecting 2 adjacent floors above basement level

Roofs

Roofs

Primary job to protect people/content from weather; shape/construction for drainage, support of snow, and wind pressure.

• Three prevalent types are (flat, pitched, arched)

• Common styles that compose these styles are

  • Pitched

  • Gambrel

  • Hip

  • Shed

  • Mansard

  • Lantern

  • Sawtooth (less common)

  • Butterfly (less common)

Flat Roofs

• Found in (commercial, industrial, multifamily residential buildings, single-family homes)

• Slope for drainage

• Chimneys, vent pipes, shafts, scuttles, skylights common features (penetrate roof)

• Parapet walls surround roof

• Fire separation walls may divide roof from neighbor roofs, from foundation up to roof

• Obstructions on roofs

  • Water tanks

  • Antennas

  • HVAC

  • Signs

  • Solar panels

Pitched Roofs

• Most common are elevated in center on ridge line, slope down to eaves along roof edge

• Shed roofs are pitched along one edge and slope down to eaves opposite edge

• Most pitched roofs use (beams/trusses) run from ridge line to top of outer wall at eaves level

• Roof decking/sheathing material (plywood/oriented strand board OSB) applied at right angles over beams

• Other applications have board/planks and void spaces between (skip sheathing)

• Roof paper applied before finish surface laid

• Finish may consist of

  • Wood/asphalt shingles

  • Asphalt rolling roofing

  • Slate

  • Tile

Arched Roofs

• Span large open areas, no columns, pillars, posts

• Made late 1800’s to mid 1900’s due to available inexpensive lumber

• Design depends on exterior walls for support

• Types are (ribbed, pleated barrels, diagonal grid {lamella}, bowstring)

Roof Construction

• 3 main components supporting structure, deck/sheathing, covering

• Can see roof coverings from outside certain construction

• Some obstruct view (parapet walls, height of building, adjacent buildings)

• Inside supports/deck maybe visible, if covered creates void spaces inches/feet thick

Roof Supports