Flood plain construction

Substantial improvement projects

A project deemed by the city to be a FEMA "substantial improvement" must bring the entire structure into compliance with current FEMA standards and the city's Flood Damage Prevention Ordinance. If your project is a FEMA substantial improvement, then an elevation certificate shall be submitted along with a planning or building permit application.

The links below explain city policy on how we decide whether a building project is a substantial improvement under FEMA regulations. Also provided is a template worksheet to assist you in calculating whether your project meets this definition. This worksheet provides only a preliminary determination. The Engineering Division will make the final decision after reviewing plans submitted with the building permit application.

Construction standards

If the project is a substantial improvement, then it will need to bring the whole structure into compliance with current FEMA standards and the City's Flood Damage Prevention Ordinance (Municipal Code §§ 12.42.51 and 12.42.52).

Engineering submittal requirements

This list of requirements will assist engineers and architects in drawing plans that the Engineering Division can review and approve quickly and economically.

Information for land surveyors

FAQs

I’m adding on to my house which is in the flood zone. What rules do I have to follow?

First, decide whether the project is a “Substantial Improvement” under FEMA regulations (see question 2, below).

If the addition is a FEMA substantial improvement, then the project must comply with FEMA regulations for building in the flood plain and with the City’s Flood Damage Prevention Ordinance. In short, these requirements include:

  1. Elevating the building above the BFE (requirements will vary on type of project - refer to question 6.)
  2. Anchoring the building to prevent flotation and lateral movement
  3. Using materials below BFE that are resistant to flood damage
  4. Using construction methods that minimize flood damage
  5. Placing utilities above the BFE (HVAC system, electrical and communication wiring, etc)
  6. Wet-flood-proofing parts the building that are below BFE

What is a Substantial Improvement?

A “substantial improvement” is any addition or home improvement project that costs more than half the value of the existing house. See the City’s guidance on how to value the existing house and the improvement project. You may also use the City’s worksheet or call the Engineering Division at 650-330-6740.

If the improvement is being made to a commercial building, the City has a separate worksheet. Call the Engineering Division at 650-330-6740.

What is a Base Flood?

This is a flood having a 1% chance of occurring or being exceeded in any given year (previously referred to as the 100 year flood).

What is the Base Flood Elevation (BFE)?

The Base Flood Elevation (BFE) is how high the water will go, in feet above sea level, when a 1% flood occurs. BFEs are shown on the Flood Insurance Rate Maps (FIRMs) for flood zones AE.

If I want to build a new house or substantial improvement in the flood zone, can the crawl space floor be below the BFE?

Yes, City Code allows the crawl space to be below BFE if

  1. The building is wet-flood-proofed
  2. The crawl space height does not exceed four feet
  3. The crawl space floor is no greater than two feet below the lowest adjacent grade

What does wet-flood-proofed mean?

  1. Finished Floor is 12" above BFE for residential projects and at or above BFE for non-residntial projects
  2. Flood vents are installed so that flood water can flow freely into and out of the crawlspace
  3. All parts of the building below BFE are built with flood resistant materials
  4. All utilities are installed 12" above the BFE for residential projects and at or above BFE for non-residential
  5. The building is anchored to prevent flotation and lateral movement
  6. The design complies with the City’s Flood Damage Prevention Ordinance (Menlo Park Municipal Code 12.42) and FEMA technical bulletins.

What are flood resistant materials?

  1. Concrete
  2. Pressure treated Douglas fir
  3. Redwood
  4. Other wood with a minimum dimension of four inches or larger (such as girders).

If I want to build a new house or substantial improvement in the flood zone, can the crawl space floor be below the lowest adjacent grade of the soil surrounding the building?

Yes, as long as these other requirements are also met:

  1. The crawl space floor is no greater than two feet below the lowest adjacent grade
  2. The crawlspace height does not exceed four feet
  3. The building is wet-flood-proofed

For a new accessory building, can the floor be below BFE?

Yes, as long as these other requirements are met:

  1. The building is used only for storage or parking
  2. The building is wet-flood-proofed
  3. The building doesn’t make flooding worse on someone else’s property
  4. The building design complies with the City’s Flood Damage Prevention Ordinance (Menlo Park Municipal Code 12.42.51 (3) (E)) and FEMA technical bulletin 7-93.

If I want to make a substantial improvement to my house in the flood zone, do I have to raise the house if the bottom of my floor joists are below BFE?

Yes. Keep in mind that a house built in compliance with FEMA regulations may be safer for you and your family if you get trapped inside during a flood. The house and its contents may also be less likely to suffer damage in a flood.

Raising your house may reduce the cost of your flood insurance. Ask your insurance agent how much you will save. Multiply the yearly savings by the years you plan to spend in the house. Compare that expense to the cost of raising the house.

Is it possible for a property owner to avoid triggering the City’s Substantial Improvement Ordinance requirements by phasing their improvements?

No, a property owner may not construct improvements to their single family house in phases with the intention of avoiding compliance with FEMA requirements.

The City encourages all building projects in the flood zone, even those that are not FEMA substantial improvements, to comply with FEMA regulations and City ordinance. Structures in compliance with FEMA regulations keep people safer, improve the City’s emergency preparedness and disaster resilience.

All projects completed less that 36 months prior to an application for a building permit are counted toward the cost of the improvement project when deciding whether it is a substantial improvement. If 36 months have elapsed between the issuance of the ‘certificate of occupancy’ for a prior project and the date of application for a new project, then only the new project is counted when determining whether it is a substantial improvement.

Can the floor of a garage which is attached to the main house be constructed below the base flood elevation?

Yes, the slab of the garage floor can be below BFE if the garage is wet-flood-proofed.

However, if the garage slab is below BFE then the lowest adjacent grade (driveway approach) will also be below BFE. This will make it impossible to reduce the cost of flood insurance by removing the home from the flood zone through the LOMA process.

When determining whether a project is a FEMA substantial improvement do I add the value of improvement projects to my house and my detached garage?

No, treat each structure separately when deciding whether the improvements to that structure are a FEMA substantial improvement.

When determining whether a project is a FEMA substantial improvement how do decide the house value if part was built pre-FIRM and part was built post-FIRM?

Calculate the value of the portion of the house that is pre-FIRM using an appropriate depreciation factor for the year when it was built. Calculate the value of the portion that is post-FIRM using a different depreciation factor for the year it was built. Add the two together.

Where is the City’s Flood Management Protection Ordinance online?

Visit the City’s website and view Municipal Code section:
"12.42.51 Standards of Construction."

Who do I call if these FAQs don’t answer my questions?

Call the Engineering Division at 650-330-6740.