HOMEOWNERS E-BOOK ON TYPES OF FOOTINGS AND HOW
TO FORM THEM.
Welcome to Homeowners Construction E-books. In this e-book I will
cover the basics for installation of footings for various structures. Since
footings are the basic foundation piece of any building, it is important that
they be designed by a licensed professional who will determine the proper
size of the footing. The local soil conditions and the size of the building
itself will determine the physical size of the footing needed, steel
reinforcement needs, if any, and so on.
Footings no matter what is intended to sit upon them such as a wall or a post
must always sit upon virgin, undisturbed earth. When excavating for your
footing with machinery (backhoe or a powered post hole digger), it is
recommended that you dig to within a few inches of the actual depth you
need and finish the last few inches by hand. This will prevent you from
accidentally disturbing the earth below the bottom of your footing forms.
IF you over dig more than you need, place the footing on that level, DO
NOT place loose material back into the hole. Your footing will settle when
the weight of the concrete is placed on it causing the entire footing to settle.
If you have already placed your foundation wall or post on the footing, the
result will be a cracked wall or a sunken post. This of course leaves you with
a structurally unsound foundation wall or a deck post that sags in one corner.
Footing TypesFootings can be formed using scrap lumber, paper tubes, and in some areas,
concrete placement is allowed directly to the earth if the hole is shaped
properly and the soil is solid enough to hold its shape. Check with your local
building department to see if this is acceptable. When a structure such as a
home or a garage is built, it is common practice to open excavate the footing
trench to allow for the forming and pouring of the footings. If this is your
type of project, any sound scrap lumber in the proper dimension of the
footing for example 2 x 8, 2 x 10, plywood, etc. is acceptable. Since the
footings will be buried, knots or holes in the lumber are no concern as
appearance is not important.
Multiple paper preformed round footing tubes set in place. Diameter
required will be shown on your drawings.
Paper tubes most commonly used for decks can be installed, poured and later
the portion of the paper exposed above ground can be peeled away to
provide a neat finished appearance. As long as the forms are strong enough
to hold the weight of the concrete until it dries and the bracing is strong
enough to make sure the form does not move during placement of the
concrete, you are good to go. Footings are usually square but can be
rectangular, round or just about any shape you can form. If you have had
your footings designed by a professional, your drawings will show the shape
and dimensions of the footings required. Look at your drawings carefully to
determine the size and number of footings required. You will most likely
want to pour them all at once to save money on the concrete orders. If you
are hand mixing the concrete, you may pour them one at a time. A typical
footing size may show as 2'-0" x 2'-0" x 10". That will be a 2 foot square
footing that is 10 inches high or deep. The drawing will also show the
elevation of the top of footing needed. Usually this shown on the footing as
(-4'-0" or -8'-0") and so on. This means the TOP of the finished footing is
four feet or eight feet below the finished floor of the building. You must set
the first floor elevation and then deduct the four feet plus the 10 inches to get
to the bottom of the new footing. Sadly it seems it is never a nice even
amount like -4'. Due to dimensional lumber sizes, masonry sizes, the
elevation will read more like (-4'-4 5/8"). It's OK. It's just a little math work.
You want to get it right though. The top of the footing will setup the finished
heights of the entire rest of your building. Get it right. Making adjustments
later on, if possible at all, can be a nightmare. If you have obtained a
building permit for your work, the building inspector will check to see if you
have set the form the minimum depth below grade required in your area.
They will NOT check your elevation for you. That is your responsibility.
Your drawings will tell you all the information you need to properly install
the footing in the right place and at the correct elevation.
REINFORCEMENTMany footings require reinforcement to strengthen the concrete. Installation
is a simple task requiring only a pair of flat nosed pliers and a roll of light
gauge tie wire. Your drawing will indicate the size and number of rebar
pieces required. If it reads 4-#5 E.W. this means you need a total of 8 pieces
of #5 rebar. Rebar is based on 1/8" increments in size so a #5 bar is 5/8" in
diameter. #6 is 3/4" and so on. E.W. is shorthand for "each way", not EastWest..
Large rebar mat installed in a footing.
Lay the bars on the flat ground using 4 of the bars in each direction
perpendicular to each other to form a mat with 4 bars facing East-West and 4
bars facing North-South, one set on top of the other. For a 2' x 2' footing,
your bars will be 1'-6" long each. Concrete protocol requires 3" of clearance
from the end of each bar to the edge of the concrete. (that is just the way it
is).
Rebar installed in lineal footings.
Using your tie wire, tie at least 50% of the cross points of the rebar. Just
wrap the wire around both bars, twist with your pliers to make the tie tight
and cut off the wire. Keeping the mat as square as possible, tie enough of the
bar intersections to keep the bars from separating when the concrete is
placed on top of them. Place the mat in your form keeping it in the bottom
1/3 of the footing height. (again protocol). This will give the maximum
strength of your footing concrete. You do not want the rebar to touch either
the forms or the earth. The concrete must completely envelop the bars. The
best way to set the rebar mat is by hanging it in your form. Using two pieces
of scrap lumber long enough to reach across your formwork, just place each
piece of lumber about 1/3 of the way in from each side. Using your tie wire,
simply hang the mat by wrapping tie wire around the bottom bars of the mat
and then tying it to the support lumber. Make sure the mat is in the bottom
1/3 of the footing when you are done. Another method is to pour concrete
into the form until it is 1/3 full, level out the concrete and then place the mat
into the wet concrete. Complete filling the form until you are done. This is
easier but if working alone it is just another task you have to do besides
pouring the concrete. Vibrate your form by lightly tapping on the sides of
the form with a hammer to consolidate the concrete and remove any air
pockets. Finish off the top of the footing level with the forms and you may
be done. If you are using round paper for tubes for a deck you may need to
set an anchor bolt for the post hanger. If you are pouring a lineal footing for
a wall,
Typical lineal footing forms in place.
You may have to install a "key" slot and rebar for the wall supports. Look
for what is called a "section" on your drawings. If a key slot is required it
will show it. This can be formed with a 2 x4 hammered down into the wet
concrete and slid along to form the key slot. The concrete must be wet
enough but not too wet or the slot will refill and not too dry or you won't be
able to form it. A little hand work with a trowel will do a fine job.
Shows lineal footing with key formed to lock foundation wall in place.
Many foundation walls require what is called rebar dowels to be placed in
the footing. You will want to have these dowels pre-bent and ready
BEFORE YOU START POURING YOUR CONCRETE. A word of
caution here as well. Splattered concrete can cause severe damage to your
eyes and skin. Wear safety glasses or goggles whenever working with wet
concrete. Any concrete you get on your skin should be washed off as quickly
as possible to avoid skin burns.
Shows footings formed with rebar dowels tied into place before concrete is
poured.
Dowels are typically bent in an L shape with a short horizontal leg and
longer vertical leg. Your drawing will tell you how long these legs need to
be. An example will read #5 dowels, 4'OC, 12"x36", I.F. This means you are
to use # 5 rebar (5/8"), bent with the short leg 12" long and long leg 36"
long. The vertical rears will go 2" in from the inside face of the wall.
They are to be placed 4' (48") on center starting from the centerline of the
wall in one corner and proceeding around the foundation. When you come to
a corner you will have more than likely, less than the 4' spacing so just add
an extra bar at that point so each corner has a bar in the center.
Keep the bars as straight as possible. The advantage to installing them before
the pour is you don't have to rush around trying to get them in before the
concrete is too dry. The disadvantage is you have to finish the top of the
concrete around each bar. "Wet sticking" rebar is sometimes frowned upon
by architects if the concrete is moved around too much. If you carefully
insert the rebar in the wet concrete making sure you have full contact with
the concrete If is usually Ok. You cannot have holes around each bar when
you are done. Layout and marking of the footing forms as to where the
dowels go, is a must. You simply will not have the time nor likely the energy
to do it after the concrete is poured. Once the concrete is hard, it is too late.
If the dowels are not installed your building inspector will reject the work.
Leveling of forms-Before you are ready to pour the concrete you must make
sure your forms are level. Using a simple 3 point level (Nikon) and a ruler,
you can with a helper take elevations every 5-10 feet or so and make sure all
the forms are the same height. The footings may have a step or two in them
which is determined by the grades on the site. Make sure each area is level
within itself. If your foundation is masonry, the steps normally measure no
more than 16" high. If the foundation is poured concrete, larger steps can be
done. Ask your architect for the maximum step allowed. In any case, each
step must be level to allow for a level surface for the foundation walls to sit
upon. In warmer climates footings may sit almost on grade. In colder
Northern climates, footings may be 4, 5 or even more feet below the ground
to the bottom of the footings. This will protect against frost heave during
very cold weather.
CLEANUPOften ignored is the cleanup portion of footing work. It is required and
foolish not to, to remove all lumber from the excavation before you backfill.
In many parts of the country termites are a serious problem. Wet wood
buried underground is a tasty morsel for these guys and when their done
eating whatever is buried, they will move UP into the building above.
Remove all wood, paper, tar buckets or other items that are not made of
earth. You want a clean excavation when you start backfilling. I have failed
more than one job over the years because the builder thought the open
excavation was a landfill. The unknowing future homeowner inherits a
potential problem and the builder saves $5 on cleanup costs. Take the time
to do it right. Tar bucket residue can weep into the soil and if you are on a
private well, could contaminate your drinking water.
Closing
Footings are a critical part of any structure that is going to sit upon them.
Take your time to get them located properly, set at the correct elevation and
the rest of your work will become much easier to do.
As a purchaser of this e-book you are entitled to one months FREE email
support for your project. I cannot offer structural information as that must be
done by a licensed professional in the state you reside in but I can offer
many tips and tricks or if you need additional information on a particular
item regarding footings, feel free to email me and I will get right back to you
as quickly as possible.
Every area of the country has its own design criteria for different kinds of
footings. Warmer areas allow for the use of pre-made footing blocks
available at big box stores. Your local building department will gladly
advise you as to the minimum required depth of
footings in your area.
Thank you for visiting and if you gained some information you didn't know
from my book you will visit again. Feel free to print a copy for later
reference during the work.
author: Peter Ackerson
This E-Book cannot be re-printed or re-published without the express written consent . A homeowner
or municipal building department is free to print for self-reference but in no case for retail sale or
other use.