Construction coexisting with trees

January 18, 2023 1:24 PM

What foundation types that are allowed by California building code will do the least damage to tree roots?

Google only wants to tell me about how tree roots can damage foundations. I want to know the opposite...

What is the best foundation for building a house in a location surrounded by trees - mostly old Oak and Bay - that have extensive root systems in the top few feet of soil? What will require the least excavation?

posted by sibilatorix to Home & Garden (5 answers total)

Palm trees have shallow, compact rootballs. If you mean large trees like oaks, getting equipment in and underground plumbing lines are bigger deals than actually scraping the foundation - it's not very deep in the south and west (assuming you aren't in the mountains). Oaks have fairly compact root systems too, that generally aren't bothered by a few roots being damaged.



You can also build your foundation up a bit.
posted by The_Vegetables at 1:48 PM on January 18, 2023

Screw/helix piles, and float the building on a steel frame mounted to the piles. Some variants require very little headroom for installation (the rig can fit into an existing basement).
posted by aramaic at 2:02 PM on January 18, 2023

Yep, helical piles will be by far the least impactful, and will also be one of the most effective supports if you have weird soils. They are also surprisingly affordable!
posted by rockindata at 3:44 PM on January 18, 2023

nthing helical piles - soil type depending (if soils rocky, but the driller will know best for your site), also helical preserves near-surface groundwater movement compared to a slab: soil water conditions changes fro9m construction are yet another way in which building harms tree health.

Helical piles are also a one-hit job and at the house scale can often be done using a long-reach excavator arm or a telehandler (search images: telehandler helical pile). The multiple operations involved in making a slab result in over-pressure effects on roots as well as compacted soil helical avoids this.

Also to install buried services consider horizonal drilling/directional drilling, or a similar type called thrust boring (up to 30metres).
posted by unearthed at 5:30 PM on January 18, 2023

There is no single statewide code governing your choice. You need to consult with your municipality's (or, if you're in an unincorporated area, your county's) building department. In my experience, they will be helpful and also advise you about where to seek additional information (from, say, a licensed structural engineer who can join you on the construction site and make useful code-compliant suggestions).
posted by Scarf Joint at 7:08 PM on January 19, 2023