Chapter 8 Heavy Timber and Mill Construction

Objectives Identify and describe the characteristics of heavy timber buildings and specific characteristics of mill construction (Type IV construction). Identify the dimensions of heavy timber members.

Objectives Describe why the misnomer “slow burning” is inappropriate for heavy timber buildings. Identify the specific hazards of these conflagration breeders. Identify specific problems with mill construction.

Objectives Identify the dangers of concealed spaces in renovated mill buildings. Identify the differences between new heavy timber buildings and those built in the past. Describe the hazards of vacant heavy timber buildings and structures under demolition.

A History of Mill and Heavy Timber Construction Buildings with noncombustible or limited-combustible exterior walls and floors made of large dimension combustible materials

A History of Mill and Heavy Timber Construction Type IV construction Origins in medieval England Early American settlements Barns and churches Courtesy of Glenn Corbett.

A History of Mill and Heavy Timber Construction Courtesy of Joseph E. B. Elliot/Library of Congress Prints and Photographs Division. Courtesy of Glenn Corbett. The Slater Mill in Pawtucket, Rhode Island, built in 1793. A reinforced concrete factory mimicking the look of heavy timber.

Mill Construction Exterior bearing and nonbearing walls are masonry. Columns and beams are of heavy timber with cast iron connectors. Courtesy of Glenn Corbett.

Mill Construction Floors are of thick grooved, splined, or laminated planks.

Mill Construction Roofs supported by beams or timber arches and trusses

Mill Construction Adequate fire barriers Ends of girders are fire cut Cast iron box Corbelled beams © Justin Kase zsixz/Alamy Images.

Mill Construction Scuppers Concealed spaces are eliminated Courtesy of Glenn Corbett.

Mill Construction Large number of windows provide maximum lighting to mill interior. Courtesy of Glenn Corbett.

Mill Construction Sawtooth mills Vertical openings are protected Automatic sprinkler system Special hazards put in detached buildings © Brians/ShutterStock, Inc.

Slow Burning? Proponents of heavy timber construction Believe “slow burning” means “collapse resistance” Statement true only if fire department can maintain interior offensive operations

Definition of Conflagration Breeder A structure that presents severe exposure problems that are capable of initiating a large, multiple building fire that is not easily contained

Characteristics of a Conflagration Breeder Radiant heat and fire brands Large collapse zones Fire spread Shut-off sprinkler systems, open equipment shafts, and uncompartmented areas

Characteristics of a Conflagration Breeder Improperly maintained fire doors Lack of compartmentation Sealed-up window openings Stair shafts Courtesy of Glenn Corbett.

Fighting a Conflagration Breeder Expect the fight of your life. You need: Large water supply Numerous heavy-caliber streams Large collapse zone Extensive brand patrol downwind Luck

Conversion, Modification, and Preservation Remodeling Often detracts from the original fire characteristics. Columns may have been removed. New trusses do not have the inherent resistance of the old columns and beams. Courtesy of Glenn Corbett.

Conversion, Modification, and Preservation Changes in use Conversions to tenant factories, storage, discount stores, and apartments Fire loads are often beyond capacity of the installed sprinklers. Unsprinklered areas are created Courtesy of Glenn Corbett.

Heavy Timber Building Requires careful maintenance Metal connectors Full fire sprinkler protection Renovations and conversion

Heavy Timber Building Concealed spaces Deficiencies should be clearly noted. Realistic prefire scenarios are required. Courtesy of Glenn Corbett.

New Buildings of Heavy Timber Construction Type IV construction Often lacks at least one feature vital for fire safety Unprotected steel columns, part-steel trusses, unsprinklered void spaces, or no sprinkler protection

Heavy Timber Structures Not being built as commonly Niche for certain types of occupancies Modern heavy timber church

Heavy Timber Structures Courtesy of Glenn Corbett Courtesy of APA - The Engineered Wood Association A laminated wood truss in a modern church. Large glue laminated timbers are used to form the roof and walls of this arena.

Heavy Timber Structures

Heavy Timber Construction Contractors Be wary of those who claim to be erecting a heavy timber structure. Many do not know the actual dimensions required.

Heavy Timber Theory Heavy timbers are difficult to ignite Will char on the surface only Over the years the floors may have been soaked with flammable and combustible fluids.

Vacant Buildings Cities with recent massive downtown fires Baltimore Philadelphia Lynn (Massachusetts) Minneapolis Indianapolis Montreal

Characteristics of Massive Downtown Fires Old combustible interior masonry buildings Fire barriers removed or inoperable Sprinkler systems removed or disabled Only fuel was the interior structure of the building

Vacant Structures Sprinklers are often turned off Open invitation to arson

Sprinkler Systems Full automatic sprinkler protection “Yard” hydrants may be turned off. Preplanning Courtesy of Glenn Corbett.

Summary Heavy timber construction has been used for large structures uniquely vulnerable to fire. Remodeling has detracted from original fire characteristics. Heavy timber construction is classified as Type IV construction.

Summary Proponents often advance the term slow burning. Slow-burning characteristic is an advantage only as long as the fire department can maintain interior offensive operations. Slow burning delays extinguishment and prolongs air pollution.

Summary A building conforming to the code definition of heavy timber construction probably lacks at least one or more of the features vital for fire safety. Full sprinkler protection is the only fire protection measure that can reasonably be expected to prevent a disaster in a heavy timber building.

Summary Problems arise when buildings are abandoned, are converted into a multiple-unit occupancy, or are prepared for rehabilitation into apartment or office occupancies. Today, heavy timber structures are not being built in record numbers. Sprinkler protection is often turned off in vacant buildings made of heavy timber.