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Adding a basement can give you more space above what is normally allowed
by Jennifer Kretschmer, AIA
Q: I would like to purchase an older home with character in San Jose. These homes often have small (barely usable) basements and foundations in poor condition. By replacing the foundation and creating a full finished basement at the same time, I can increase the living space. What are the potential issues I might face in doing this- what should I be aware of or concerned about?
A: Creating a full finished basement under an existing house is an expensive and timely process, but in certain areas can be well worth it. That's especially true if you are already at the maximum floor area allowed for your city. In San Jose the maximum floor area ratio (FAR) for most single family homes (not requiring a special review) is .45 represented as 45% of the square footage of the lot. For example, a typical lot in San Jose is around 6000 square feet. With a FAR of .45 the maximum square foot for the house would be 2700 square feet. In San Jose you may be allowed a larger FAR if you apply and go through the review process called a “Single Family House Permit.” This special review will cost more in city fees as well as increase the time it takes to review the home with the Planning Department.
A full basement gives you extra square footage that is not included in that FAR calculation in San Jose. However, some cities do include basements in their FAR calculation, so check with the local planning department to confirm the city regulations regarding basements.
The new basement will have to comply with current building codes including ceiling heights, egress (exit) wells, stairs and possibly a sump pump/sewage ejector. You will also need to hire an architect and/or structural engineer to do calculations and design the concrete foundation structure.
The new basement, which will be the new foundation for the house, will need to have hold downs that anchor the wood structure of the home to the foundation. It is also likely that the original house will have to have shear walls added to it. Shear walls are walls that are anchored to the foundation with anchor bolts and have special plywood and nailing. The walls must be continuous from the foundation to the roof framing and should not have any openings cut through them.
While the foundation is being built, the house will be raised on a few steel beams. The house may be raised up in this precarious position for a few months and the house should not be occupied during that time.
The price for such an endeavor is determined by how much work will need to be done to the existing house, the construction of the concrete walls and floor of the basement as well as architect, engineering, and city/county fees.
For more detailed information on residential basements in San Jose please visit the Building Department’s website:
http://www.sanjoseca.gov/building/Building.asp and download the document titled, “Basement Policy.”
by Jennifer Kretschmer, AIA
Q: I would like to purchase an older home with character in San Jose. These homes often have small (barely usable) basements and foundations in poor condition. By replacing the foundation and creating a full finished basement at the same time, I can increase the living space. What are the potential issues I might face in doing this- what should I be aware of or concerned about?
A: Creating a full finished basement under an existing house is an expensive and timely process, but in certain areas can be well worth it. That's especially true if you are already at the maximum floor area allowed for your city. In San Jose the maximum floor area ratio (FAR) for most single family homes (not requiring a special review) is .45 represented as 45% of the square footage of the lot. For example, a typical lot in San Jose is around 6000 square feet. With a FAR of .45 the maximum square foot for the house would be 2700 square feet. In San Jose you may be allowed a larger FAR if you apply and go through the review process called a “Single Family House Permit.” This special review will cost more in city fees as well as increase the time it takes to review the home with the Planning Department.
A full basement gives you extra square footage that is not included in that FAR calculation in San Jose. However, some cities do include basements in their FAR calculation, so check with the local planning department to confirm the city regulations regarding basements.
The new basement will have to comply with current building codes including ceiling heights, egress (exit) wells, stairs and possibly a sump pump/sewage ejector. You will also need to hire an architect and/or structural engineer to do calculations and design the concrete foundation structure.
The new basement, which will be the new foundation for the house, will need to have hold downs that anchor the wood structure of the home to the foundation. It is also likely that the original house will have to have shear walls added to it. Shear walls are walls that are anchored to the foundation with anchor bolts and have special plywood and nailing. The walls must be continuous from the foundation to the roof framing and should not have any openings cut through them.
While the foundation is being built, the house will be raised on a few steel beams. The house may be raised up in this precarious position for a few months and the house should not be occupied during that time.
The price for such an endeavor is determined by how much work will need to be done to the existing house, the construction of the concrete walls and floor of the basement as well as architect, engineering, and city/county fees.
For more detailed information on residential basements in San Jose please visit the Building Department’s website:
http://www.sanjoseca.gov/building/Building.asp and download the document titled, “Basement Policy.”