Best to use fill or excavate on basalt rock for residential foundation
Best to use fill or excavate on basalt rock for residential foundation
(OP)
I am in the process of getting excavation bids to lay the foundation of a residential home situated in central Washington on basalt rock. The garage (4 car) will be slab on grade and the remaining 1 story home on crawl space.
The slop has a 4.5' grade, from north to south, and I don't want the foundation to go over 4' if possible due to county engineering requirements.
A septic system also needs to be installed.
I also don't want to go dig too low and lose the view (lot sits on a cliff).
My question is which is the best way to go? Should I excavate, which has many unknown factors due to the rock, or go with fill.
I am a first time General Contractor/owner/builder. This first step could be potentially one of the most expensive of the project.
Any thoughts, ideas, suggestions would be extremely helpful
The slop has a 4.5' grade, from north to south, and I don't want the foundation to go over 4' if possible due to county engineering requirements.
A septic system also needs to be installed.
I also don't want to go dig too low and lose the view (lot sits on a cliff).
My question is which is the best way to go? Should I excavate, which has many unknown factors due to the rock, or go with fill.
I am a first time General Contractor/owner/builder. This first step could be potentially one of the most expensive of the project.
Any thoughts, ideas, suggestions would be extremely helpful





RE: Best to use fill or excavate on basalt rock for residential foundation
By GC/owner/builder, does that mean you're going to own the thing when you're done? If I were you, I'd start with a pretty detailed geotechnical investigation, including soil borings, to determine exactly where the rock is. You should also get perk tests where you think you're going to put your septic field, and hire someone to design it before you get too happy with your lot layout. If the infiltration rate is too low, that septic field could get a lot bigger than you think.
Outside of the septic issues, your question becomes one of cost. Price trucking fill dirt to the site, price blasting rock, then raise/lower your building pad on your grading plan until it's the cheapest. Pretty typical grading VE exercise.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Best to use fill or excavate on basalt rock for residential foundation
Is it a septic tank that you're considering? You'll need to get a copy of the local regulations and plan this to be near the road for occasional emptying.
RE: Best to use fill or excavate on basalt rock for residential foundation
RE: Best to use fill or excavate on basalt rock for residential foundation
RE: Best to use fill or excavate on basalt rock for residential foundation
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Best to use fill or excavate on basalt rock for residential foundation
Using fill only, gets the house higher than I originally wanted, but it also improves our already spectacular view. We would do decking instead of patio.
RE: Best to use fill or excavate on basalt rock for residential foundation
Cheers