Building Design and Construction Handbook - Merritt - Ventech!

WALL, FLOOR, AND CEILING SYSTEMS 11.19
temperatures over 2000�F, minimum height above any part of the building should
be 20 ft.) Masonry chimneys should be constructed of solid masonry units or reinforced
concrete and lined with firebrick or fire-clay tile. In dwellings, thickness
of chimney walls may be 4 in. In other buildings, the thickness of chimneys for
heating appliances should be at least 8 in for most masonry. Rubble stone thickness
should be a minimum of 12 in. Cleanout openings equipped with steel doors should
be provided at the base of every chimney.
When a chimney incorporates two or more flues, they should be separated by
masonry at least 4 in thick.
In seismic zones where damage may occur, chimneys should be of reinforced
masonry construction. They should be anchored to floors and ceilings more than 6
ft above grade and to roofs.
Fireplaces should have backs and sides of solid masonry or reinforced concrete,
not less than 8 in thick. A lining of firebrick at least 2 in thick or other approved
material should be provided unless the thickness is 12 in.
Fireplaces should have hearths of brick, stone, tile, or other noncombustible
material supported on a fireproof slab or on brick trimmer arches. Such hearths
should extend at least 20 in outside the chimney breast and not less than 12 in
beyond each side of the fireplace opening along the chimney breast. Combined
thickness of hearth and supporting construction should not be less than 6 in. Spaces
between chimney and joists, beams, or girders and any combustible materials should
be fire-stopped by filling with noncombustible material.
The throat of the fireplace should be not less than 4 in and preferably 8 in above
the top of the fireplace opening. A metal damper (12 ga or thicker) extending the
full width of the fireplace opening should be placed in the throat. The flue should
have an effective area equal to one-twelfth to one-tenth the area of the fireplace
opening.
11.6 PROVISIONS FOR
DIMENSIONAL CHANGES
In design and construction of masonry walls, allowance should be made for relative
movements of the masonry and contiguous construction. If this is not done, unsightly
or troublesome cracking or even structural failure may result. In the past,
such damage has occurred in masonry walls because of:
1. Restraint offered by contiguous construction to dimensional changes in the masonry.
Such changes may be produced by temperature changes or by absorption
of water by the masonry after construction.
2. Restraint offered by the masonry to movements of or dimensional changes in
contiguous or bonded construction, such as concrete frames or backup walls.
Such changes may be produced by drying shrinkage, elastic deformations under
load, or creep of the concrete after construction.
To avoid such restraints, it is necessary to install in walls expansion joints with
proper gaps, at appropriate intervals, and to break bond between the walls and
construction that would restrain relative movements (Fig. 11.10).
Vertical expansion joints should be installed in masonry walls to permit horizontal
movements of the masonry, and horizontal expansion joints, to permit vertical
movements. In the absence of specific information on thermal and water-