Is building a foundation below frost line necessary?

A lot of small / tiny houses use concrete deck blocks for their foundations. Is it not necessary however to build the foundation below the frost line to prevent frost heave?

Tiny houses on blocks may have more to do with:

1)  Ability to pick up and transport, considered non permanent structure and therefor cost less in Municipal land tax, and require fewer permits.
     Because they sit on blocks on the ground there is little in the way of frost heave that would damage the structure.

2)  Buildings on foundations are considered "immobile" and Municipal by-laws require building permits, and land tax is greater.

Cheers!  K

From what I've seen, I think it has a lot to do with how the tiny house is constructed. Like many sheds, they are designed to be mobile and to be moved. So, they are constructed on a trailer frame or built on a very sturdy and aggressively cross-braced timber frame. As a result, they don't really sag and deform.

If the tiny house is permanent and depends on the foundation for its structural strength, though, it is wise to go deep with the pilings. Otherwise, cracks and ill-fitting windows and doors, and even water incursion will make you miserable. Screw pilings, which you can generally install yourself, have a threaded "jack" section at the top that lets you adjust the height in case of unexpected movement. They work great for decks; I think they would be excellent for tiny houses as well. My 2c.

In northern MN, I have seen people float barns on top of the soil.  The one I have followed up on was built about 1978 and is still standing.   It measures around 40 x 60 ft.  I have also seen houses over 100 years old built in same way. In all cases the foundations were railroad ties or similar. In all cases the soil had a high amt of sand.  Now, I would hope, we could select something other than ties.

Agree with the need to know what type of TH being planned. Could be small and mobile enough to sit on skids or trailer; could be a TH on a foundation, requiring similar foundation types as are used in other stick-built homes.

If a permanent foundation is desired, then you have all the choices that are typical for your area, and that you or the homebuilder (and engineer?) is comfortable with designing and installing; building codes are also in play.

Having said all that, perhaps a frost protected shallow foundation (FPSF) can be utilized in your area ...

Regardless of foundation type, you can't spend enough time and money in making sure water is kept away from the foundation or pad area; raising height of pad, swaling water away from the pad, draining water with french drains to daylight, sealing/insulating, etc. Once the foundation is done, there is less opportunity and interest to go back in and fix issues.

Up in the Canadian North (in the tundra), there are vast areas of muskeg (peat) which can be 50ft deep. The general solution is to excavate it all out and then fill the hole with crushed rock that they excavate from a nearby rocky formation called an esker.

It's extremely expensive and difficult to do (just getting the heavy equipment in is a major undertaking), and the availability of above ground rock is quickly diminishing.

Engineers are trying a lot of different alternative systems, one being where the building sits on concrete blocks, which in turn sit on Styrofoam blocks that distribute the weight over a larger surface area. The concrete blocks have a threaded rod set in them, and the building has a coupling that allows for it to be levelled periodically as the underlying foundation rises and falls.