Foundation - First Task
The location of the foundation is determined by the site survey or plot plan. The plot plan will show all
property line setbacks, dimensions, easements, and any other normally determined by flood plane
restrictions or city and county codes. The surveyor can provide a marker or benchmark that serves
restrictions that might be required. Another important item required for the foundation is the elevation of
the foundation. The elevation is normally determined by flood plane restrictions or city and county codes.
The surveyor can provide a marker or benchmark that serves as a reference to establish the finish floor
elevation (FFE). In order to be able to start the foundation, the building pad needs to be complete. If fill
dirt is required, it needs to be compacted and rough graded to the correct elevation Once the pad is
complete and the corners established, batter boards can be put up. The batter boards and string lines will
allow you to get a true picture of the footprint Once the pad is complete and the of the house and finish
floor elevation. After the string lines are checked for correct dimensions and corners established, batter
boards can be put up. The batter boards and string lines will allow you to get a true picture of the
footprint of the house and finish floor elevation. After the string lines are checked for correct dimensions
and being square, you will be ready to start putting up forms and digging footings. The foundation forms
can be wood as in most residential construction or metal as in commercial construction. Once the forms
are set, they need to be braced off in order to prevent the concrete from pushing the forms out. After the
foundation forms are set and braced, the underground plumbing can be installed. The plumber can use
the form boards to lay out the position of the plumbing walls and pull string lines. With the plumbing wall
lines in place, the plumber can dig the plumbing ditches and be sure that the plumbing is installed correctly.
After the plumbing is installed, the ditches should be left uncovered until inspected by county or city
inspectors. Sanitary lines are checked for slope and for leaks. Sanitary lines should have at least a 1/4 inch
slope per foot. The sewer lines are checked for leaks by using a ten foot stack test. The stack test is
accomplished by extending the main vent stack, usually a 3 inch PVC vent up ten feet. The whole house
sewer system is then filled with water up to the top of the ten foot vent stack. All the underground
plumbing connections are then checked for leaks.
Concrete is one of the main building products used in the construction of a house. Depending on where
the concrete is used in the construction process, it can become a very critical factor in the overall
structural strength of the house. Just because the concrete comes premixed in the concrete truck does
not mean that the concrete is always good.
In normal residential concrete, the first conversations might be with the concrete company's outside sales
person. The size of the foundation and how much concrete will be required are usually the first questions
to be answered. The quantity of concrete is expressed in "yards". One cubic yard of concrete is equal to
twenty seven cubic feet of concrete. An example would be if there was a hole three feet wide, three feet
long, and three feet deep it would require one yard of concrete to fill the hole. Another value that is used
when pouring sidewalks and driveways is that a yard of concrete will cover eighty one square feet of area
(driveway or sidewalk) when the concrete is four inches thick.
The next issue discussed might be the strength of the concrete. Years ago, the only strength concrete
used in house foundations was 2000 psi (pounds per square inch) concrete. It's not unusual today to see
builders pouring 3000 psi and 4000 psi concrete, depending on the size and complexity of the project.
Some of the larger homes are designed by an architect and might require a structural engineer. The
structural engineer might require mix designs from the concrete company for his approval.
The sales person might ask next what kind of "slump" is required. This is sometimes where the concrete
subcontractor and the builder might try to reach a compromise. The lower the slump the greater the
strength but the harder the concrete is to work. The higher the slump the lesser strength but the easier
the concrete is to work. When a structural engineer is involved, he might specify that the concrete is to
be 3000 psi with a three to five inch slump. If this is specified, it is very important to stay within these
limits do not allow anyone to add water to the mix on site without permission from the individual doing
the testing. If the concrete is being pumped, there are additives that can be added to the mix in order to
allow a higher slump but not jeopardize the strength of the concrete. These additives can also be used in
dry and windy climates to allow a wetter mix and hopefully prevent surface cracking due to the fast
dehydration of the concrete. If the concrete is tested, the slump might be checked every fifty yards and
the cylinders might be taken at the same interval. Concrete cylinders are taken and tested to verify the
compressive strength of the cured concrete. The cylinders are compressed and broke at specified
intervals. A cylinder broke after 28 days should break at the designed strength or greater.
Also, usually the temperature of the concrete will be checked at this time. The temperature of the concrete might become more of a factor in the summer rather than
the winter. A rule of thumb might be that if the concrete temperature is above 95 degrees it is not acceptable to pour in the foundation or footings. Sometimes a good
starting point to monitor the temperature of the concrete in a truck is to check the ticket and see when the truck was loaded at the plant. In warmer climates, the
longer the concrete is in the truck the hotter the mix. In cooler climates the temperature might not be out of range but the time in the truck might become a factor.
Usually a rule of thumb might be that, if it has been forty five minutes to an hour since the truck was loaded, the load may have started setting up and might not be
acceptable to use.
As you can see there are a few more things to consider in foundation concrete other than just pouring the concrete out of the truck. As in most any other
construction process, a little pre-planning and basic knowledge might prevent a major mistake that could cost a lost of time and money.
As stated previously, the foundation is one of the most important phases in the construction of a house. This phase will require you to be familiar with
reading plans, dimensions, and formulas to determine quantities of required materials. Some of the more common quantities will be expressed as
length, width, depth, linear feet, board feet, square feet, cubic feet and cubic yards. All the materials in the foundation will be ordered and bought with
one of these descriptions. In order for you to be able to estimate and order materials correctly, there are certain formulas that can help you calculate
the correct quantities of concrete.
The following formulas are ones that will be necessary in order to calculate and order the required material for your foundation.
Linear Feet is probably the simplest quantity to calculate. Lumber yards sometimes sell lumber by the linear foot which makes it easy to calculate the
cost per piece.
Linear feet = number of items X the item length
220- 2 x 4's lumber X 16 feet in length = 3520 linear feet
Lumber is one of the main items that might be bought by the linear foot for a foundation. If you dig footings, labor might be charged by the linear foot.
Board Feet will add two other dimensions to calculating the cost of materials. Lumber suppliers sometimes sell their lumber per thousand board feet.
A board foot is one linear foot of lumber - one foot wide - one inch thick. A 1x12 piece of pine which is 12 feet long will equal 12 board/feet. In the same
way a 2x6 piece of pine 12 feet long will equal 12 board/feet.
Board feet = Linear feet X ((thickness inches X width inches) / 12 inches)
(3520 linear feet of 2x4) X ((2-inches X 4 inches) / 12 inches) = 2347 Board Feet
Lumber may be sold by the board foot form the building supply. The board foot price will be expressed so much per thousand board feet. Example: 2 x
6’s might be sold as 565.00 per M (Thousand board feet). This will equal .565 cents per board foot.
Square Feet is a simple process of multiplying the length X the width. You will need to know how many square feet there is in the foundation in order
to estimate how much vapor barrier to buy and to determine how much the termite pre-treat will cost.
Square Feet = Length X Width
Cubic Feet adds one other dimension to square feet. This dimension is depth. Items that require you to know the amounts of cubic feet are fill dirt and
concrete. Concrete and fill dirt are both sold by the cubic yard. There is 27 cubic feet in a cubic yard of fill dirt and concrete.
Cubic Feet = Length X Width X depth
Cubic Yard is used to determine how yards of concrete or fill dirt might be needed for the job. There is 27 cubic feet in a cubic yard of fill dirt and
Cubic Yard = Total Cubic Feet / 27 cubic feet
Category Construction Glossary