What are the foundation options for a prefab house?

Richard Bowie
Updated: Nov. 23, 2020

I am trying to decide on a suitable foundation for a 1200sqft prefab house to be shipped in 2 sections, with a final resting place in the mountains of western BC.  The site slopes along the long axis of the house approximately 3 feet over 50 feet.

I've considered the following options, each with it's pros and cons:

1. Screw Piles: Pros are speed of installation, minimal site grading, no curing time, high capacity for foundations, elevated foundation to manage slope, access to utilities and low cost.  Cons are insulation challenges under the skid and enclosing requirements under the house.

2. Concrete Piers: Pros are low cost (marginally higher than screw piles), low tech so I could install myself, elevated foundation to manage slope, access to utilities and all materials are easily accessible.  Cons are excavation and site grading required, cure time, and the same insulation and skirting requirements as screw piles.

3. Frost wall and crawl space: Pros are conditioned space for utilities and HVAC, elevated foundation to manage slope, prevents critters in crawl space and some storage.  Cons are managing moisture, cost, and cure time.

4. Slab on grade: Pros are insulates under skid, protection of underskid utilities and ease of installation.  Cons are doubling up of insulation with skid being on concrete, management of sloped site and curing times.

Overall it's a bit of a toss up so I'd like to see if there are key advantages or challenges I'm not clear on for my application.

Thanks in advance.


Responses (2)

Richard Bowie 3 years ago

Thanks for the quick response.  The double insulation I meant was that the slab would be insulated and then I will put an insulated skid on top of it.  Would there be any point in putting anything more than a small amount of insulation in the skid?

Further, a lot of the slab will be structurally redundant due to the skid.   

The other issue is the amount of dirt work to achieve a level base for the slab while not creating drainage issues by having the slab notched into the slope.