Ask Andy – What Foundation is Best

by Andy Sheldon

in Ask Andy, Designing

I was recently asked what type of foundation is best for a small cabin. Unfortunately there really is not one right answer.

What are the typical foundation types?

  • Basement
  • Crawlspace
  • Slab on grade
  • Pier and Beam
  • Skids
  • Wheels

Each foundation type has its pros and cons and which will be the best for any situation will be based on many things, such as:

  • Your land
  • Your budget.
  • Your needs.
  • Your soil conditions

Let’s look at each type and see if we can determine where they might be best used.

Basements:

Basements are usually the most expensive solution but also offer extra area for storage and mechanical equipment. They are best used in well-drained soil conditions or where you have enough slope in a lot to “drain to daylight”.  A leaky basement is worse than no basement at all. Also basements generally require good access for construction equipment to excavate. Basements also are economical when you have a decent slope for a walkout basement or where the footing depth for frost is so deep that the extra cost for a basement is very small.

Crawlspaces:

Crawlspaces are generally less expensive than basements due to the less masonry and less excavation required. They are best used in flat or moderately sloping lots or where the footing depth for frost is shallow or where there is rock that would prevent the installation of a basement. Crawlspaces can also contain “lowboy” types of mechanical equipment, and if ample access is provided and the crawlspace is dry, it can be used for storage. Ductwork is also easily installed in crawlspaces.

Slabs on Grade:

This type of foundation is generally less expensive than a crawlspace. It will work best on substantially flat land where the frost depth is not too deep or where there is little access for larger excavation equipment. If there is a significant amount of bedrock or shale that makes excavation expensive, difficult or impossible, the slab on grade maybe your best choice. The disadvantage is that it offers no storage or mechanical space and running utilities under the slab must be done initially before the slab is poured and cannot easily be altered later. Depending on the finished floor material, some people may feel the floor is too hard.

Pier and beam:

This foundation type is also called “post and beam” or “column and beam”. The cabin is supported by beams instead of a perimeter foundation wall and the beams are supported by piers, posts, or columns. This type of foundation is good to use for lots that are environmentally sensitive. The piers offer little disturbance to the natural drainage. They are also appropriate for sloping lots, difficult to excavate rocky lots, complicated conditions or areas that might be subject to flooding like shore or coastal areas.

Skids:

The advantage of this type is that it is inexpensive. Basically skids are similar to the pier and beam foundation where the skid acts as the beam. But instead of being supported by piers, the skid is continuously supported by the ground, usually on a bed of compacted crushed stone. This provides a level and well-drained surface.

This is best used in level conditions and where the there is little frost. Since there is no part of the foundation that is below frost, the cabin can be subject to frost heaving in cold climates. This is generally not a problem for garden sheds, but for a finished cabin it could be. If the cabin is small enough, like a tiny house, then the building will be small enough to rise and fall as one unit with the frost. The disadvantage is that you must build in flexible connections to the utilities in colder areas.

Wheels:

This type of foundation has become popular with the tiny house movement. The basic benefit obviously is that the tiny cabin becomes easily movable. The best source of details for this type of foundation can be found in Jay Shafer’s  Small House Book.

Do you have have any foundation questions? Please leave a comment. As always, your comments are very valuable not only to me but to the others who drop by.

Best,

Andy