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

Leave a Comment

{ 10 comments… read them below or add one }

thomas harmon June 25, 2013 at 3:27 pm

what would be a good foundation for a 14 foot by 24 foot cabin with loft? Location is tough to get to,off a rocky logging road. the building site is in a pine grove ridge with a little slop. Ground has roots and big rocks in the soil.?

Reply

Andy Sheldon September 3, 2013 at 7:44 am

I would suggest a pier and beam foundation. This will lift the cabin off the rocks and roots and will be much easier to build. You can normally find and area with a root structure to place a pier and if you hit bedrock, you can anchor directly to that as well.

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Jordo April 15, 2013 at 11:15 am

Wondering what you would recommend for me. We are going to build on really rocky ground in northern BC Canada and would like to avoid getting concrete brought in because of expense. I’ll be building a 16 x 24 cabin, single floor with a large loft. Can’t seem to pin down an effective way to build a foundation. We will have access to a small (D3) dozer for a couple days but other than that its all hand work.

Reply

Yuri June 16, 2013 at 8:55 am

You might want to take a look at a diamond pier foundation – pinfoundations.com. No real digging is involved. I am in New England and we have similar soil.

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DMS52 February 24, 2012 at 12:40 pm

Andy My wife and I own some acreage on the Gasconade River in Missouri. We are going to put a cabin there but we want to elevate the cabin above the 500 year flood plain. Is there a special type of concrete to use for the piers?

Reply

Andy Sheldon February 24, 2012 at 8:09 pm

Concrete that cures under water is actually quite strong. My biggest concern would be to use the correct reinforcing that would not be affected by salt water. Flood waters are also a very strong force, and so you should have the piers engineered for your location and circumstance. The engineer who designs the piers will be able to specify the exact concrete and reinforcing to use for your conditions.

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Ernest February 17, 2012 at 10:19 am

We had some real trouble when digging a foundation because we hit ledge and our hole was filling with water. We had to design an complicated drainage system to get the water to day light. Here is an interesting article that may be a good add on to your information:

http://aghbuilders.com/archives1462/

Thanks,
Ernie

Reply

Andy Sheldon February 17, 2012 at 2:32 pm

Thanks Ernie… Looks like it could have been a real mess. As we all know… Mother Nature always wins.
Best, Andy

Reply

Andy Wilson February 12, 2012 at 6:12 pm

Hi Andy,
Thanks for the nice concise outline of the many ways to set out the foundation of the building.
Can I put in a plug for timber post foundations in non freeze locations with a simple array of bearers and joists built to whatever the local code allows for spans and spaces?
This is topped by plywood or panelfloor sheets plus insulation between the joists and a vermin barrier to keep rats out of the insulation.
Poured concrete slabs have a huge amount of embodied energy and generally need professional help while the timber floor can be done by an owner builder and mistakes can be identified and rectified at leisure. Nothing worse than 12 tons of ready mix going off as you struggle to fix a problem with the clock ticking!
The ply flooring sheets automatically square up the job and cross walls come out exactly at right angles using sheet edges as guides.
Every amateur builder needs to spray can the words Level, Plumb and Square on a large sign at the worksite and read aloud this mantra each morning. Saves an infinity of bad words later!
I love your buildings, keep it up and thanks.
Andy Wilson

Reply

Andy Sheldon February 13, 2012 at 3:57 pm

Thanks Andy,
To be honest, post foundations just slipped my mind. If done correctly, the footers and posts can be set below the frost line and work for cold weather too. “Pole Barns” have been using this type of construction for some time, although the barns usually do not have a wood floor system. Thanks again for the reminder…
Andy

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