22

Recommended Practice Concrete House
Construction
AT
the convention of the American Concrete
Institute last month the Committee on Con-
crete Houses, of which Emile G. Perrot is chair-
man,
submitted as its
report a tentative draft of
recommended practice for concrete house con-
structoin. The report is confined to a considera-
tion of the monolithic, unit constructed and plast-
ered
types. It probably will be revised before its
final presentation and adoption by the Institute,
the main features of the report follow.
This recommended practice shall apply to the
construction of house not over three stories in
height and not exceeding 30 ft. in height between
top of first floor and under side of third floor ceil-
ing.
(a) Basement and foundation walls of mono-
lithic concrete shall be not less than 6 in. in thick-
ness and shall he supported on a concrete footing
or basement floor sufficient to prevent settlement
of the building The design of these footings
shall be based on the ability of the foundation
soil to carry loads and the monolithic character
of the concrete wall and footing or basement floor
shall he considered in determining the required
hearing area on the soil. Basement walls shall
he designed to resist the horizontal pressure of
the earth in contact with the exterior of the wall.
(b) Basement walls of precast units bonded
together hv registering or interlocking projec-
tions or depressions, grouted in place, or by re-
inforcing bars across joints embedded in cement
mortar, shall have a minimum thickness of 7
in., or not less than the minimum thickness of ex-
terior bearing wall of superstructure. The pre-
cast units shall conform in strength, quality and
absorption to the requirements of Recommended
Specifications and Building Regulaions present-
ed by the Committee on Concrete Products of the
American Concrete Institute.
Note I.—Allowing a total of 50 lb. per square
foot roof load, 75 lb.
per square foot for second
and third floors, and 100 lb.
per square
foot for
first floor, including weight of walls, the unit com-
pressive stress per square
inch on a 6-in. base-
ment wall would he slightly in excess of 100 lb.
The unit stress produced by the overturning ef-
fect of the wind on the side of the house would
not materially increase this. The effect of the
pressure on earth filling against the house is in
a majority of cases small as compared with the
verticle load of the superstructure and cannot
materially affect the stability of a monolithic or
properly bonded
precast unit wall.
Walls.
(a) The thickness of single exterior bearing
walls of plain concrete shall be not less than 4 in.
thick, but when reinforcing in excess of 2 to 1
per cent is used, the thickness shall be determined
by the usual method of reinforced concrete de-
sign for verticle loads and for a uniform wind
load of 30 lb. per square foot on exposed surface.
(b) The thickness of the bearing wall, of
double or triple concrete walls shall conform to
paragraph (a), this section, except that the thick-
ness required to carry the loads may be reduced
by the actual working shear value of ties between
the walls.
(c) Exterior walls which act merely as curtain
walls between reinforced concrete columns or
studs shall be designed to withstand a wind pres-
sure of 30 lb. per square foot on the
exposed sur-
face. Reinforced concrete curtain walls
may be
constructed by plastering and back
plastering on
expanded metal or wire mesh reinforcement, or
shot with a cement gun or by other mechanical
means of placing concrete or stucco.
(d) Exterior walls of precast units bonded
together by registering or interlocking projec-
tions, grouted in place shall conform in thickness
to the schedule of wall thickness provided for
concrete block, brick, tile and architectural trim-
stone of the Recommended Building Regulations
presented by the Committee on Concrete Prod-
ucts of the American Concrete Institute, except
that large or small reinforced concrete units con-
nected on two opposite ends to structural mem-
bers designed to carry all loads to foundations
originating from the
weight of the building or
from wind
pressure or which in themselves act
as structural members may have a thickness de-
termined by the
bending stresses produced by
wind
pressure of 30 lb. per square
foot to the ex-
posed surface.
(e) Solid concrete exterior walls shall be furn-
ished with furring on the inside so as to produce
an insulating air space between the interior finish
and the concrete walls. Double exterior concrete
walls, providing a dead air space between, may he
finished without further provision for insulation.
Floors.
Reinforced concrete floors shall he designed to
carry a live load of 40 lb. per square foot uniform-
ly distributed. The
advantage of continuity in
reinforced concrete floors shall not be assumed
unless the concrete is placed continuously over
intermediate supports for the entire length of
the floor, with appropriate reinforcing to take
care of
negative moments.
Roofs.
(a) Flat concrete roofs shall be designed to
carry the dead weight of the roof and 20 lb. per
square foot additional for houses constructed in
climates subject to heavy snowfall. Sloping roofs
shall be designed for 30 lb. per square
foot on the