When building a small cabin it is important to set that cabin on an appropriate foundation. Fortunately, when dealing with small structures, you have many options not available to standard house construction. Quite literally a small cabin can be set right on the ground using treated skids if that is your desire. But there are several options to be discussed here such as the traditional concrete foundation, pillar foundation, and skid foundation.
A Word About Floor Joice Spans in a Small Cabin
Before you begin construction of your foundation, it is important to give some thought to what type of floor joists you will use and how far they will span. In general floor joist spans are as follows
Lumber size 16" centers 24" centers
2x8 12' 10'
2x10 15' 13'
2x12 19' 16'
If you decide to go with smaller lumber for your joists, keep in mind that you may need a beam along center of the joist section to cut down the span to a reasonable amount. If you need to install a beam, it's a good idea for the beam to be supported every 6' or so along its length.
Building Traditional Foundation for your Cabin
The traditional concrete foundation is by far the sturdiest and most expensive. Most likely it will require you to employ a contractor for completion. One alternative you have is to not poor concrete but to lay concrete blocks in its stead (you may consult other sources for description on how to lay blocks). Either way you will need to start by determining the frostline. For poured and pillar type foundations you should be certain that you are around 12" below frostline. Your local building inspector can tell you how deep frostline is in your area.
Once you have determined the frost line depth, you need to layout the foundation at the building site. A good way to start is with stakes drove into the ground and contractor string. For a 16x24 cabin you will try to create a 16x24 rectangle with the string. Use a string level to insure it is all level. Then measure diagonally from corner to corner to ensure the building is square.
Once everything is square, you can mark under the string with orange marking string. Remove the string and it is now time to start digging out the foundation. Many a foundation has been dug by hand with a shovel. You might, however, try searching your local rental stores. Sometimes a backhoe can be rented for a reasonable price for this purpose.
Building the Pier Foundation for your Cabin
Laying out the pier foundation isn't a hole lot different than laying out the traditional foundation. In fact you can layout the footprint with string using the method outlined above. The difference is that you do not need to dig out a trench below frostline around the entire length of the building. You simply need to mark every four foot along the string and dig a hole 12" below frostline.
You may bury treated 6x6 posts in each of the holes if you like. Recomended method is to use sona tubes. Set the tubes in the holes and fill with concrete, setting an anchor bolt in the center of each. Additionally, these tubes can be poured seperately if you cap off one end so that you have a canister(For example see: http://mlhalloutdoors.com/?page_id=82).
Metal post anchors can be attached to the top of the concrete pillars. The post can then be attached to the pillars and cut to lenth to facilitate leveling of your floor. If you decide, however, to just bury the posts in the ground then it is advisable to at least set them in concrete.
Building a Skid Foundation for Your Cabin
This is the simplest form of skid foundation. It consists of treated 4x4, 6x6, or nailed together 2" lumber the length of the cabin. No digging is necessary and light loading is expected so only consider this type for smaller cabins.
Depending on your desires and how much clearance you want underneath, it is important to select the skids appropriately. The most clearance can be had by nailing together treated 2x12 lumber. How far apart and how many skids will be needed is dependent upon floorjoice spans and lumber types.