Selecting and Building Your Small Cabin FoundationThe foundation keeps your small cabin wooden frame structure from being placed directly on the ground where it would be more susceptible to rot and insects.
The choice of your small cabin foundation primarily depends on the ground type, how level it is (slope), availability and cost of related materials, and whether you intend to hire a professional building service contractor or to do it the work yourself.
- Prefabricated concrete blocks (precast piers)
- Poured Concrete
- Pressure Treated Timber
- Posts (locked in concrete or sona tubes)
Small Cabin Foundation Guidelines and Suggestions:
- If the ground is rocky OR there are a lot of tree roots underground, digging holes (for posts) may be a problem
- If the ground has a small slope, you may be able to compensate with different-sized, or additional blocks, or raise the ground level on one side by laying gravel.
- If the ground has a fairly steep slope, you will need to use posts or raise a wall from concrete blocks on low-level side.
- It is not recommended to place concrete blocks directly on the ground, unless it is bare solid rock. Blocks should be placed on a flat rock/slab and/or gravel, and be well leveled.
Make sure any gravel is compressed/stomped well. Otherwise it will settle later and skew your cabin structure.
- One of the advantages of using concrete blocks is that over time, some blocks may settle more than others. This can be fixed by slightly lifting one side of the cabin with a car jack and shimming the blocks with flat stone, ceramic tile, etc.
- If using posts, they normally should be dug into the ground deep enough to firmly hold their load and below the freezing level. The freezing level depends on your geographical zone. Generally, you should dig the post at least 4 ft deep.
- If pillars or posts are not dug deep enough (i.e., above the frost line), this may cause warping or movement within the structure over time as moisture in the ground freezes and thaws. Cabin structure warping can lead to cracked windows, skewed doors, etc.
- If a post cannot be dug into the ground, another option is to place it into a concrete footing or a concrete (deck) block. However - very important - this can only be done on some (1 or 2) support points. Posts that are not secured deeply will not withstand horizontal forces. Other supports points (posts/blocks) that can withstand these forces must be firmly mounted.
- When placing posts into the ground, it is recommended to use concrete footing, at least in the top half. Sona tubes are supposed to be even better options, but they require more concrete, are more labor-intensive and cost more money as a result.
- Poured concrete is an applicable option only on a well-leveled ground. However, it is also a more expensive and more labor-intensive option.
- For posts you can use prefabricated pressure-treated 4"x4" or 6"x6" posts, or wooden posts formed using tree trunks. (You can paint them with oil paint first for better protection).
- Sometimes the best option is to place the entire structure on a set of two double support beams (sometimes called girders). This is especially useful on unlevel ground, when used in conjunction with posts. Use two (or more) double-sets of 2"x10" or 2"x12" beams. (Keep in mind that beams add height to the cabin floor - your small cabin will look and feel "raised").
Also, see other small cabin foundation options on our Forum pages.I chose prefabricated concrete "4-way" deck blocks for the construction of my small cabin foundation. In addition, I had to do minor ground leveling using flat stones and some gravel. These concrete deck blocks are inexpensive ($7 apiece), easy to do work with, and offer better hold of the cabin floor frame than plain rectangular concrete blocks or slabs.
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