Major Changes to the Title 24 Building Code

From insulation to ventilation, here's what builders will need to know.


Residential Envelope


  • Above Deck Roof Insulation is no longer a prescriptive option.
  • Below deck insulation is still a prescriptive option. New insulation requirements below the roof deck increased from R-13 to R-19 in climate zones 4, 8-16. For multifamily, R-13 is allowed in Zones 10 and 16.
  • The location of ducts and AHU in conditioned space is still an option.
  • Builders can still use above deck insulation with performance modeling.


In Climate Zones 1-5 and 8-16 requires more wall insulation. High-performance walls are specified with a u-factor reduced to 0.048. That reps a 2x6 wall with R-21 insulation in the cavity and additional 1” rigid (R-5) installed on the outside of the wall.


This is any wall with density greater than 45 lbs/cu.ft. There are two options for compliance:

  • Interior insulation R-13 Continuous (R-17 in Zone 16)
  • Exterior insulation R-8 Continuous (R-13 in Zone 16)


  • Two options for compliance:
    • Interior insulation R-13 Continuous(R-15 in Zone 16)
    • Exterior insulation R-5 Continuous (R-10 in Zones 14-15, R-19 in Zone 16) QII Quality Insulation Installation (QII) is now required on most residential buildings under prescriptive compliance.
  • Insulation can have no voids.
  • It requires insulation by a HERS Inspection of insulation in under floor, wall, roof ceiling, air barrier. Inspections must be done before the walls are closed up.
  • It will set the baseline in performance approach. This is prescriptive Not mandatory but if you don’t do it you will have a 10-15% hit in terms of compliance.
  • Applies to new construction as well as additions larger than 700 square feet.
  • It is not required for multifamily in Climate Zone 7 (Coastal San Diego).


  • Maximum U-Factor 0.30
  • Maximum SHGC 0.23
  • No requirement in Zones 1, 3, 5, and 16
  • Zone 16 is now treated like the other heating zones (above), not like the cooling climate zones. In all the heating zones, passive design to take advantage of heat gain is encouraged.
  • All climate zones basically require an R-5 insulated door; includes doors to outside and to unconditioned spaces but does not apply to doors from the house to the garage.
  • Subject to a maximum NFRC rated U-factor of 0.20
  • Doors with 25% or more glass now treated as a window and must follow the window requirements.


  • Extended walls that are 2x6 require R-21 insulation
  • QII required on additions larger than 700 square feet
  • Attic insulation in additions 700 square feet or less:
  • Zones 1, 11-16 require R-38
  • Zones 2-10 require R-30
  • Rafter roofs can be R-22 using the performance approach offsetting the penalty.



  • An exception for ducts in support platforms and wall cavities to be uninsulated.
  • Minimum 2” filter (larger face area formula will allow for 1”)
  • Minimum MERV 13 filtration
  • Filter not required if 10 feet or less of ductwork. MERV 13 filter not required for alterations to existing systems, only to new systems (new ducting, AHU and condensor)


Fan wattage must be HERS tested on forced air system with cooling to be no more than 0.45 W/cfm if the unit is a gas furnace aligning with the new furnace efficiency requirements starting in July, 2019 for the Department of Energy.. Other air handlers such as heat pumps and fan coils can still be 0.58 W/cfm. Small Duct High Velocity Forced Air Systems must test at 250 cfm per ton and no more than 0.54 W/cfm.


The CEC released a more stringent calculation for how airflow is calculated. It will result in significantly more IAQ CFM (or airflow) required for the home. (For new multifamily dwelling units must include either a balanced ventilation system, a continuously operating supply ventilation system or a continuously operating exhaust ventilation system. If using a continuous system, it requires HERS blower door testing to show no more than 0.3 cfm/sf leakage based upon the envelope surface area.)


Hoods must be HERS inspected in the field to verify:

  • Minimum airflow per ASHRAE 62.2 (100 cfm)
  • Maximum sound ratings per ASHRAE 62.2 (3.0 sones)
  • Other airflow options are provided in ASHRAE 62.2 for continuous ventilation


  • Heat pumps that are high efficiency (HSPF greater than 8.2) must be HERS verified in the field.
  • Heat pump heating capacity values at 47 degree and 17 degree ratings must be HERS verified in the field when non-default sizes are used in performance modeling.
  • Whole House Fan airflow and rated wattage must be HERS verified in the field.
  • Central Fan Integrated Cooling systems must be HERS verified in the field.


  • Applicable to units serving individual dwelling units
  • Any number of gas or propane tankless water heaters
  • A large gas or propane water heater (greater than 55 gallons) must be accompanied by windows with a U-factor of 0.24 or less and one of the following (all of which must be HERS verified):
  • Compact hot water distribution
  • All piping insulated
  • A drain water heat recovery system


There are two pathways to compliance. Mixed fuel pathway with the baseline being a gas water heater, and electric. The most viable approach is to use a Tier III NEEA rated unit (must increase the PV size by 0.3 kW in Zones 1 and 16)

Others include:

  • Compact hot water distribution HERS verified plus
  • A drain water heat recovery system HERS verified
  • Or in Zones 2-15 increase PV size by 0.3 kW
  • Or in Zones 1 and 16 increase PV size by 1.1 kW


A replacement water heater can be one of the following:

  • Natural gas or propane unit
  • An electric resistance unit if no gas is at the water heater location
  • If no natural gas, may replace an electric water heater (60 gallons or less)
  • A heat pump water heater located indoors in climate zones 1-15


Luminaire Requirements: Night lights, step lights, and path lights require a vacancy sensor if light is over 5 watts or 150 lumens. Light source internal to drawers, cabinetry or linen closets require a vacancy sensor if light is over 5 watts or 150 lumens unless they are equipped with controls that automatically turn the lighting off when closed. In bathrooms, garages, laundry rooms and utility rooms there needs to be at least one luminaire controlled by either a vacancy sensor or an occupancy sensor (must be configured in Vacancy Sensor mode before final).


This is applicable to units serving multiple dwelling units (central system), and still requires a solar system:

  • 20% net solar fraction in Zones 1-9
  • 35% net solar fraction in Zones 10-16  You can reduce the NSF by 5% if each dwelling unit has a drain water heat recovery system HERS verified.