Type III Ordinary Building Construction

Type III Ordinary Building Construction

• This chapter provides general information about Type III ordinary building construction classification.
• Each member is responsible for exercising appropriate control as dictated by their rank when implementing this manual chapter.
• Ordinary construction is the oldest form of masonry construction.

General Information

• Exterior and structural members are made of noncombustible or limited combustible materials.
• Interior partitions, floors, and roofs are made of combustible materials like wood.
• Wood joists are used as simple beams spanning from wall to wall, usually parallel to street frontage.
• Roof construction may mirror the floor construction or be peaked using rafters or trusses.
• A cockloft or void space is common between the top floor ceiling and the roof.
• Structures typically range from one to four stories, but can reach six stories in height.
• The wood used is smaller in size and dimensions than in Type IV Heavy Timber Construction.

Walls

• Walls must be masonry and considered structural to qualify as Type III Ordinary construction.
• Veneers can disguise the actual construction type if the walls are not structural.
• Non-reinforced masonry walls usually have a maximum height of six stories.
• Exterior wall thickness is dependent on the building's overall height.
• The minimum depth is generally 8 inches, with taller buildings having walls up to 30 inches thick.
• Walls thicker than 9 inches diminish in thickness as they rise, necessitating a larger foundation.
• Common bearing walls or party walls are typical in this construction.
• Adjoining buildings share the same bearing or party wall, visible at the roof line extending past roofing materials.
• In older structures, floor and roof joists from both buildings may sit in common wall sockets.

Materials Used

• Modern load-bearing masonry walls use materials like brick, concrete block, and stone.
• Brick is produced from locally available clays and shales in various sizes.
• Concrete blocks are common concrete masonry units ranging in multiple sizes and shapes, with the nominal size being an 8x8x16 inch block, which can be filled with cement or other materials for strength.
• Stone consists of rock pieces removed from a quarry and cut to the desired shape and size, including Limestone, Sandstone, Brownstone, Granite, Marble, and Slate.
• Exterior masonry walls are interconnected by metal trusses or common wall ties.
• Courses are horizontal layers of individual masonry units, strategically placed including brick and concrete block for strength and appearance.

Types of courses

• Stretcher Course has bricks placed end to end.
• Soldier Course has bricks placed vertically on end.
• Header Course has bricks placed with the end facing out, alternating with other courses for a stronger horizontal bond between two withes, which is a single vertical column of masonry units in a wall.
• Openings for windows and doors must be provided.
• Supporting the weight of masonry units poses a design problem.
• Mortar joints between bricks or blocks provide little tensile strength, requiring a lintel, arch, or corbelling over openings.
• The presence of an exterior masonry wall does not confirm that a building is of “Ordinary Construction”.
• Interior structural framing includes combustible columns that transfer loads to the exterior bearing walls.
• Combustible wood materials will be finished with plaster, drywall, or other interior finishes for fire resistance, which creates concealed combustible void spaces similar to Type V Wood Frame construction.
• Wall voids are created by framing walls, with the depth of the upright wall studs creating a wall space.

Roof/Floor Construction

• Commonly consists of wood joists resting on the masonry wall in a beam pocket.
• The end of the joist is cut at a fire cut, which allows the beam to fall away freely from the wall if failure of the beam occurs.
• The fire cut allows the floor to collapse down without pushing the masonry wall outward.
• Lightweight trusses or laminated wooden I-beams are common in newer construction for floor and roof assemblies.
• Older constructions used thicker tongue-and-groove wood boards interlocking together.
• Roofs were made of 1” to 2” thick wood planks laid side by side.
• Newer construction utilizes plywood or oriented strand board (OSB).
• Roof coverings include wood shingles, asphalt shingles, rolled asphalt, clay/slate tiles, tar and gravel, or a rubber roof.

Strengths

• Durability and resistance to weather, fire, and insects of masonry components.
• A strong construction method if properly maintained.

Weaknesses

• Common void spaces throughout the building.
• This causes concern for undetected fire travel.