Will a 24 inch wide, 8 inch thick, Footer work on my two story home when we don't know the soil condition. The Blue Prints say around 14 inch wide and 6 inch thick,but we need to be very safe and we only get one shot at this project. Please advise or give your option.Answer:
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First of, footing sizing depends on a lot of factors. You mentioned soil condition, that is one factor. Since you don't know the soil condition, 1500 psf is the number to use for unknown soil condition.
The short answer to your question is if you feel more comfortable with 8 inch thick by 24 inches wide, I think that will work fine. A two story building is not very heavy that will require much bigger footing.
Myself being an islander, I can relate to your life in the Philippines. Islands are more susceptible to high winds. Your footing will help stabilize the building to withstand high wind from hurricane and such but you will need a very Sophisticated calculations in order to come up with heavier footings that will counter the wind effects. That will be a topic for another day.
The weight of the building is another very important factor that help determine the size of footing. If your building is wooden walls, and wooden floor joists, beams, trusses, etc - that would mean your dead load will not be as heavy as a structure made from concrete or block framed structure, or even structural steel.
If you can calculate how much your building weighs and divide that total weight by two assuming you have two sides of the building that have footings. Use that number divide by the length of one side of the footing - that will give you pounds for every foot of footing. Whatever your result here divide by the 1500 psf mentioned above. Your answer should be a number between 1 and 2 for every foot of footing. I'm sorry if I have lost in this but it's kind a complicated.
If you can give me a sketch of the framing and how the floor and roof frames works, I can help you better.