Mild Climate Footings
In mild winter climates
(12" or less frost depth) and well drained non-clay soil, there is
little chance
of freezing soil lifting the footings and piers. In this case you can
dig down into the soil and either pour a concrete footing
or fill the footing hole with clean crushed rock. The size of this
footing hole should be a 16" diameter circle or square for gravel or
rocky soils and a 24" circle or square for soils with mostly loam,
loose sand or gravel. The footing depth should be 1/2 the width or
more.
This foundation is used in the Little
House Plans kit.
Make sure the bottom of the footing rests
on undisturbed soil free of organic material. Don't build on fill or
soil that has been dumped on the site (unless it is incompressible
material such as crushed rock). Your footings will spread out the total
weight of the building over the bearing soil. Good solid material under
these footings is essential. When in doubt, make the footings larger
thus reducing the load per square foot (think snowshoes).
Note-1: This simple Little House foundation has been built even in quite
cold climates with well drained soil that does not expand when freezing
(such as clay) see this
owner built home story.
Note-2:
This is the most inexpensive and lightweight foundation option for a
small building. It would not be appropriate for larger, more expensive
houses or in areas of high wind or on steep sloping ground.
Cold Climate Footings
In colder climate areas
or locations with expansive clay type soils you need the footing to be
at
the bottom of a deeper hole
so that the bottom of the footing sits on soil that is below frost
depth. Coming up from the footing will be either a pressure treated
wood post or a concrete pier made out of mortared blocks or a
poured tube. Pour a concrete footing first with a cross of 1/2"
(#4)
rebar to reinforce and tie into the pier. Set these bars on rocks or
broken brick so that they sit 3" up from the bottom of the pour. Wire a
section of rebar vertical and this will tie into another bar running up
the core of the concrete pier. Overlap sections of bar 12" to 15". The
center of your tube or block pier will be poured with concrete and tie
the footing and beam straps or brackets together with a reinforced
concrete pier. The tube pier is shown at left - (Note: Your inspector
may require more rebar). A secondary advantage of
this concrete pier is that it has much better anchorage against
uplift and wind forces. Getting the beams level and in the right
place is most easily done by screwing or lightly nailing the metal
connector to a beam stand-in such as a couple of long 2xs, leveling
this "beam" in its
proper
location with temporary bracing and then filling the tube or cutting
the posts. The beam can then be assembled in the brackets and any
final adjustments made.
These foundation details are part of the
following small house building plans:
Block Piers
You can also build your
piers from 8 x 8 or 12 x 12 concrete blocks. For short piers use the
smaller blocks, for taller ones go larger. Tube piers come in various
diameters as well and larger ones should be used on the downhill side
of a sloping site where they will stand higher. A safe rule of thumb is
that a pier or post should not exceed 12 (for concrete) or 20 (wood)
times its width in unsupported height. Confirm this with your building
inspector or a local engineer.
When using concrete blocks for your piers,
the footings must all be level in order for the piers to be level under
the beams. If you have to change footing levels they must be in 8"
increments. With poured tubes you can cut them off level prior to
filling so the footings can be at different levels. Check for level
using an inexpensive water level made from clear tubing. Run this from
footing to footing or from tube to tube using the shortest pier as the
master.
Setting
the Tops of the Piers
Set the height of the
piers so that there is a minimum of 12" under the beams and 16" under
the floor joists of the floor platform. This will provide enough space
for plumbing, wiring and
insulation to be worked on from below.
Wood Post Foundation Piers
When using wood posts
get foundation grade 6x6 treated poles or posts. When using
a gravel footing, nail a square of pressure treated 2x10 to the bottom
to act as a foot. Use only hot dipped galvanized, "Z-max" or stainless
steel nails and bolts with PT material. Don't rely only on the bolts to
hold the beams. Notch the posts and then bolt or set the beams directly
on top of the wood posts and connect them with appropriate metal
brackets or wood plates as shown.
There are many different types of metal
brackets and strap anchors. Ask locally at the lumber yard as these
will vary by brand and the size of beam and post. A "Y" anchor that is
nailed to both sides
of the beam is sometimes more available than the Simpson hardware shown
in the diagrams.
Treated wood posts can be packed with crushed
rock or soil
cement made from 5 to 10 parts clean gravel and sand type
soils (no organic material) to 1 part cement. Mix well and add only
enough water to make workable. For longest service, the post holes
should drain and not hold water against the posts. You can also extend
service by painting the posts with asphalt roofing tar for 8" either
side of the final soil line. This is where posts are most likely to
experience organic attacks.
These foundations can be used to build
most of the cabin and small
home plans from CountryPlans.com. Most of our plans also
include other foundation options where post
and pier is not appropriate. These detailed plans have all the needed
structural information such a beam sizing, spacing of the piers and the
design and insulation of the platform
floor.
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