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Foundation Work
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Adding the foundation framing - Month 1-day 17 |
installing the rebar - Month 1-day 22 |
the foundation pour - Month 1-day 23 |
the curing slab- Month 1 Day 25 |
Rainy Day and the beginning of framing.
Month 1 day 30 |
SUBSTRUCTURES
Excavation
The objective of the excavation is
to provide a safe and adequate support for footings and foundations.
Adequate clearance is needed to ensure protection against damage by decay
or insect attack. Good excavation also provides drainage for and access to
basement-less space.
The process usually involves
several steps. First, the location of the house is staked out by the
builder or surveyor and the topsoil is removed to a point where it is
stored during the construction process and re-spread as the final step in
the finish grading. Then the main hole is dug‑first, usually with the help
of a power shovel and then by hand to a depth 6 to 10 inches below the
floor level. Finally, trenches are dug for the footings and service pipes,
drains, dry wells and septic tanks.
Excavations for footings and
foundation walls should extend at least 6 inches into natural, undisturbed
soil to provide adequate bearing except where bearing is on a stable rock
formation and below the prevailing frost line.
Footings and Foundation Walls
The objective of the footing is to
provide support for the dwelling without excessive differential or overall
settlement or movement. The footing is the parametric base of concrete
that is laid by pouring the concrete into wooden forms set at a level
below the frost line and on undisturbed earth. All substructures will
settle to a certain extent unless they are located on solid bedrock.
Also,. excess shifting and settlement will cause cracks and leaks in the
foundation wall and uneven floors in the house. Thus, local building codes
specify the required depth for each region based on the local frost‑line
depth.
Because the foundation must
provide safe and adequate support for all vertical and lateral design
loads, all foundation walls are poured or laid on top of the footings.
Block walls must be properly laid and well mortared, then filled with
concrete and made watertight with cement plaster or other waterproofing
compounds. Cinder blocks are porous and thus are inferior to cement blocks
for a solid foundation. Brick and tile, although good foundation
materials, are costly and require substantial skill for proper laying, as
does stone, which once was very popular in the Northeast.
The three basic forms of
foundations, basements, crawl spaces and slab‑on‑ground. With the
exception of those houses being constructed in the northern portions of
the country, fewer and fewer houses are being built with basements. And,
where basements are built, there is an increasing trend to gain additional
living space by finishing portions into family rooms, utility areas, baths
and lavatories, workrooms, kitchens and even bedrooms. In the event that
the house has a basement, the height between the basement floor, which is
constructed similarly to a slab, and the bottom of the joists usually is 7
1/2 to 8 feet.
For basement-less houses, the
finish grade is a major factor in the choice between slab‑on‑ und or crawl
space as a foundation. For slab‑on‑ground construction, the finished
ground grade must fail sharply away from the house to prevent flooding.
Slabs are constructed by first building footings for support, although
some slabs, known as "floating slabs," are built without them. The
excavation then is covered with gravel and a vapor barrier and insulation
is installed around the edge.
Crawl spaces, which provide
flooding protection and also provide a convenient place to run heating
ducts, plumbing pipes and wires that must be accessible for repairs, are
constructed similarly as well as basements except that the distance from
the floor to the joists is 3 to 4 feet. The floor can be concrete, as in a
basement, or it can be dirt, often covered with a vapor barrier. In
northern regions, crawl spaces must be insulated or heated to prevent
pipes from freezing and floors from becoming cold.
A Wet or Damp Basement
Dampness is, of course, the main
problem with basements, for it damages wall and floor coverings,
furniture, clothing and other possessions. It also poses a health hazard ‑
‑especially when the basement is used for sleeping. Some of the causes of
basement dampness that can be thwarted by the careful builder are poor
foundation wall construction, excess ground water not properly carried
away by ground tiles, poorly fitted windows or hatch, a poorly vented
clothes dryer, gutters and downspouts spilling water too near the
foundation wall and a rising water table in the ground.
A basement that is wet or damp
only part of the year usually can be detected any time by careful
inspection. All the walls should be checked for a powder‑white mineral
deposit a few inches off the floor. Only the most diligent cleaning will
remove all these deposits after a basement has been flooded.
Stains along the lower edge of the
walls and columns and on the furnace and hot water heater are indications
of excessive dampness, as is mildew odor.
The causes of a wet and damp
basement are numerous. Some are easily corrected and others are almost
impossible to correct. In areas where the soil drainage is poor or the
water table is near the surface of the ground, well constructed footing
and foundation drains are needed to maintain a dry basement. They should
be installed when the house is constructed because this is expensive to do
afterward. The same is true of a vapor barrier under the basement floor,
which is very easy to put down during construction but impossible
afterward.
Cracks in the floor and walls may
be patched with various widely marketed compounds. A more drastic step is
to dig down and repair the wall from the outside.
What first appears to be a major
water problem might be traced to a leak in a window or the hatch door. A
simple caulking job will stop the water from coming in. Water will leak in
through a window at the bottom of a well that does not drain properly in a
heavy rainstorm. Extending the drain line or deepening the dry well stops
this problem.
The earth around the house should
slope away from the foundation wall so ground water will not collect along
the edge of the foundation. If there is an edge of the roofline without a
gutter, water may be running off and collecting next to the foundation
wall. The water that is collected by the gutter and flows into the leaders
must be diverted away from the foundation wall. The leader should run into
a sewer drain, dry vent or splash pan‑in that order of preference.
Dampness and mildew also may be
caused by moisture condensing on the walls, ceiling and pipes. Proper
ventilation eliminates this problem.
Main Bearing Beam and Columns
Because most houses are too large
for the floor joists to be spanned from one foundation wall to the
opposite foundation wall, one or more bearing beams resting on columns or
piers are used to support the floor joists. If only one beam is required,
it runs roughly down the center of the basement or crawl space.
Steel beams, because of their
great strength, can be used to span longer distances than wood beams of
the same size. Steel beams, however, are subject to fire damage from
relatively low heat. A steel beam will lose some of its strength at 500
degrees and at 1,000 degrees will buckle under a normal load. Beams that
are covered with metal lath and plaster, on the other hand, will maintain
their strength under much higher temperatures for long periods of time.
Wood beams, although not so strong
as steel, often are used and are quite satisfactory. When a solid beam is
used, it generally is 6 by 8 inches to 10 by 10 inches. Plank beams
consist of several 2‑inch by 6‑inch to 2‑inch by 10‑inch planks placed
side by side on end to achieve the desired thickness.
Most beams are supported by wood
posts, brick or block piers or metal Lally columns that are
concrete‑filled steel cylinders. The post, pier or column must rest on a
footing, which should be at least 2 feet square and I foot thick. If brick
and block piers are used, they should be at least 12 inches square but
preferably 16 inches square. If wood posts are used, they should be set on
a platform several inches off the floor so that any water on the floor
from leaks will not rot them. Steel columns require caps and base plates. |
Drilling the Piers
Pouring the piers
Diligent
Inspection Services