Which foundations are used in ADU’s?

Foundations are critical as they bear and distribute the load of your home. They also prevent groundwater and soil vapors from getting into your home to protect it from mold & warp. Below are a few of your most popular choices:

  • Basement
    • Most expensive option.
    • Provide a lot of value, add square footage to your home without increasing your footprint.
    • If the water table runs higher on your property – probably not the best location.

  • Slab
    • Most common type of foundation in CA
    • Usually one of the cheapest options
    • Less maintenance than other foundations
    • Earthquakes + expansive soils (Clay) will cause these foundations to crack. Post tension cables in the slabs have helped prevent cracks. 
    • Ground should be faily level, not a great choice when there is a slope

  • Crawlspace 
    • Can be used in place of or with a slab foundation
    • Footings are poured then cinder blocks are placed on top to support the house’s walls. 
    • Positioned a few feet above the ground (hence a ‘crawlspace’, which leaves an opening underneath the structure.
    • Plumbing repairs are easier because you have a space beneath the home.
    • Provide protection against moisture
  • Pier and Beam
    • Piers are drilled into the soil to rest on rock which in turn support beams to support the house.
    • House is less likely to shift around as a result of movement in the soil directly underneath your home.

  • Helical Piles
    • Provide foundational support for structures of all types and sizes. Just like old-fashioned pile-foundations, helical piles (also referred to as screw piles, helical piers, helical anchors, etc.) are embedded deep underground in order to disperse the enormous weight which sits atop them. 
    • Multiple piles are installed to create a platform, on which a building can rest.

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