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Residential Additions Guidelines


                        TABLE OF CONTENTS

  • Background
  • Energy Requirements
  • Plot Plan
  • Enforcement
  • Sample Plans


The purpose of this handout is to provide direction to those wishing to provide additional floor space to their homes. This handout is intended to provide information regarding the planning, plan preparation, permit, and construction inspection processes.

The addition of living space usually takes one of two forms:
1. Living area constructed within the existing foundation, such as rooms downstairs;
2. Living area constructed outside the original foundation, such as a one or two story rear addition.

Generally, adding rooms downstairs is feasible if the rooms do not or intrude into required parking areas. Additions to the outside of the house are limited by the lot coverage ordinances. Contact the Planning Division for specific lot coverage information at (650) 991-8033.

Prior to designing an addition, it is a good idea to visit the Planning and Building Divisions in City Hall. Staff will provide specific information regarding the requirements and regulation of the proposed project. This initial direction may save time and money.


After consulting with the Planning Division regarding parking and lot coverage, design and preparation of plans may begin.

The City requires three complete sets of plans be submitted for review. A set of plans consists of:

  • A plot plan
  • Floor plans
  • Any required elevations and details
  • Energy calculations

Three complete sets of plans are to be submitted. This enables all City divisions and departments to review the plans simultaneously, thereby saving you time. The minimum paper size for plans is to be 11 inches by 17 inches or larger. Sample floor and plot plans are attached (see pages 9 and 10).


The City does not require plans be prepared by an architect or engineer in most cases. This includes:

  • Construction of rooms downstairs, inside the original foundation;
  • One and two story additions prepared in accordance with the conventional light-frame construction provisions of the California Building Code (CBC).

Second story additions and one or two story additions not meeting the CBC conventional construction provisions require drawings prepared by a California registered architect or engineer. Supporting calculations will need to be provided demonstrating structural compliance with the building code. The designer's wet stamp and signature will need to appear on the first page of the calculations and on each plan sheet.


Applications for rooms down and additions must be accompanied by Title 24 energy calculations. Forms CF-1R and MF-1R signed by the owner and designer must appear on the plans.


The plot plan shows the layout of the house on the lot. Plot plans are normally drawn on a one eighth inch (1/8") to one foot (1') scale. The plot plan must show:

  • the length and width of the lot;
  • the location of the building structure(s) on the lot with the new and existing portions clearly indicated;
  • the length and width of the existing and proposed driveway;
  • utility connections;
  • if the project is an addition, the method of carrying roof runoff from the addition to the street is to be shown.


Floor plans are drawn on a ¼" to 1' scale. Floor plans must include:

  • all floors, the garage and all rooms;
  • the usage and ceiling height of each room;
  • all plumbing fixtures, existing and new;
  • windows, including existing and proposed, and indicate size and type;
  • doors, including size and type;
  • all proposed electrical fixtures, switches, outlets and smoke detectors in the addition;
  • furnace, water heater and the laundry facilities.

Clearly indicate what is new and what is existing.


Plans for additions outside the existing foundation must include details and elevations.
Details should include:

  • footing/foundation design;
  • the method of attachment of the addition to the existing structure at the foundation, each floor level, and the roof;
  • a flashing detail;
  • a nailing schedule;
  • a plan for erosion control during construction;
  • details for any other feature which may require additional explanation.


The CBC requires smoke detectors be installed when rooms are added or additions are made to single-family homes. Install smoke detectors:

  • in each (existing and new) bedroom or sleeping area, and
  • at points centrally located outside of each bedroom or sleeping area.

Smoke detectors are to receive their power as follows:

  • in existing construction, from a battery;
  • in new construction, from the building's electrical system with a battery backup.


The installation of a fire separation is required when additional living space is created. When new habitable space is added, the garage is to be insulated and sheetrocked as follows:

  • Insulate walls with R-13 insulation and floor/ceiling assemblies adjoining living spaces with R-19 insulation.
  • Sheetrock walls supporting living space above, and walls and garage floor/ceiling assemblies separating the garage from living space.
  • Sheetrock must be 5/8 inch thickness type - X, fire-rated material.

The water heater, if located in the garage, must be raised:

  • The code requires the unit be elevated so that the flame is a minimum of eighteen inches (18") above the floor. This eliminates a potential fire hazard.
  • Strapping the water heater to prevent movement during earthquakes is also required.

For more information, obtain the water heater handout from the Building Division.

The use of plastic piping materials for plumbing drain, waste and vent systems is not permitted. This material is more subject to fracture than metallic piping in the event of an earthquake.

The City requires all new roof assemblies to have a minimum Class B fire rating. For more information, obtain the roofing requirements handout from the Building Division.

Compliance with these special code requirements will need to appear as notes or details on the plans as applicable.


A completed application form is to be submitted along with building plans. It is a simple application that may be completed in advance, if you wish. Applications are available at the Building Division.

A plan check fee is collected at the time of application. The fee is dependent upon the size and extent of the proposed construction work.

Plans are normally reviewed within ten (10) working days. Or you may take advantage of Express Plan Check:

  • Express Plan Check is available on Tuesday mornings between 8:00 and 10:00 a.m.
  • It provides same day plan review.
  • Single story residential additions or rooms constructed within the existing walls are eligible for Express Plan Check.

Following completion of the plan check, the City will mail you notification either approving or denying your application:

  • If approved, permits are ready to be obtained and permit fees will be calculated. You will need to come into our office to pay these fees and obtain the permits prior to beginning work.
  • If denied, you will receive a list of plan check comments. Plans will need to be revised and resubmitted to comply with the comments.


Permits may be obtained by the homeowner or a licensed contractor:

  • A homeowner may obtain permits if he/she or the immediate family intends to do the work.
  • If the work is to be done by others without compensation, the owner will need to furnish proof of worker's compensation insurance.
  • If the work is to be done by others for compensation, the permit will need to be obtained by a State of California licensed contractor.

After paying permit fees and obtaining permits, the work may begin. As work progresses, inspections must be obtained before any work is covered or concealed. Normally, inspections are scheduled for the following:

  • Foundation (before concrete is placed)
  • Underfloor plumbing
  • Framing
  • Rough electrical, plumbing and mechanical
  • Insulation
  • Sheetrock nailing
  • Final inspection

Inspections are scheduled by telephoning our office before 3:30 p.m. the working day before you need the inspection. You will be given the choice of a morning or afternoon inspection. Inspection hours are normally between the hours of 8:30 and 12:00 and 1:30 and 5:00 Monday through Friday.

You may call our office between 8:00 and 8:30 the morning of the inspection to obtain a more specific time.

PLEASE NOTE: If the work inspected is found to be incomplete or incorrect, or if no one is present when the inspector arrives, a reinspection fee in the amount of $70 will be charged. This fee covers the City's cost of having to return to the site for another inspection.

Rooms are not to be occupied or otherwise used until a final inspection has been approved.


  • A building permit expires if work is suspended or abandoned for a period of 180 days.
  • The building code requires the permittee make substantial progress on the construction project and schedule an inspection within this time period to maintain an active permit.
  • If a permit expires, it will need to be renewed before work may recommence.
  • Permit renewal fees will need to be paid.


If your application was submitted as a result of the City undertaking enforcement action on your property, it is important that the application materials be approved, permits be issued and the work be completed in a timely fashion. Lapses in any of these processes will result in resumption of enforcement action and incurring of enforcement fees at our standard hourly rate for staff time incurred.


For zoning, parking and lot coverage information, contact the Planning Division at (650) 991-8033.

For building code, application, or permitting requirements, contact the Building Division at (650) 991-8061.


When the house does not have a fire-resistive occupancy separation between the house and garage, provide 5/8" type X gypsum board on all walls and ceiling of the garage; and provide R-13 insulation in the walls between the habitable space and garage and R-19 insulation in the ceiling of the garage (DCMC 15.08.060).

2. OCCUPANCY SEPARATION DOORS. Provide a self-closing, tight-fitting solid wood door 1-3/8" in thickness, or, a self-closing tight-fitting door having a fire-protection rating of not less than 20 minutes between the garage and habitable areas (CBC 302.4, Exception 3).

3. WATER HEATERS - PROTECTION FROM FIRE DAMAGE. Water heaters generating a glow, spark or flame capable of igniting flammable vapors may be installed in a garage, provided the pilots and burners or heating elements and switches are located at least eighteen inches (18") above the floor level in residential garages (DCMC 15.20.060).

4. WATER HEATERS - PROTECTION FROM SEISMIC DAMAGE. Water heaters shall be anchored to resist horizontal displacement due to earthquake motion (CPC 510.5).

5. CEILING HEIGHTS. Habitable space shall have a ceiling height of not less than 7'-6". Kitchens, halls, bathrooms and toilet compartments may have a ceiling height of not less than 7'0" (CBC 310.6.1).>


a. New bedrooms or legalized bedrooms: Provide smoke detectors, hardwired with battery backup, in all bedrooms and adjacent spaces.
b. Existing bedrooms; Provide smoke detectors, battery operated, in all existing bedrooms and adjacent hallway or spaces.

7. HEATING. Dwelling units shall be provided with heating facilities capable of maintaining a room temperature of 70 F at a point 3 feet above the floor in all habitable rooms (CBC 310.11).

8. PLUMBING PIPING. Note on the plans: no plastic plumbing pipe allowed (DCMC 15.20.040 and 15.20.090).

9. RESIDENTIAL ENERGY REGULATIONS. (State Title 24, Climate Z.3).
(a) Provide Residential Energy Calculations - revised January 1992.
(b) Provide Certificate of Compliance CF-1R form on the plans.
(c) Provide Mandatory Measures MF-1R form on the plans.
(d) Provide notes on the plan for R-value of the insulation called for on the energy calculations.
(e) Provide notes on the plan for the U-valve of all exterior windows and glass doors called for on the energy calculations.
(f) Provide notes on the plan for the general fluorescent lighting in the bathroom and/or kitchen called for on the energy calculations.

10. BEDROOM EMERGENCY EGRESS. Specifying openable dimensions of the proposed bedroom window on plan. Bedroom window for purposes of emergency escape and rescue shall have a minimum clear openable Width dimension = 20 inches; and minimum clear openable Height dimension = 42 inches (CBC 310.4).


Sample Plans