Builders: Title 24 for a Tract That Spans Two Climate Zones

The 50 percent rule, step by step

Section 150.1(a)3 requires a single-family building to meet the performance or prescriptive standards for its climate zone. Its exception then says that where a single contiguous subdivision or tract falls in more than one zone, all buildings in it may be designed to the zone that contains 50 percent or more of the dwelling units. It counts dwelling units, not acreage.

1. Confirm the tract is one contiguous subdivision, then count the planned dwelling units in each climate zone, using the zone boundaries the Commission publishes in Joint Appendix JA2.
2. If one zone holds half or more, you may model every plan to it.
3. State the chosen zone on the submittal so the plans examiner can see the basis.

The rule says "may", so each lot can still be modeled in its own zone.

Why it matters

The Commission has defined typical weather data, prescriptive packages and energy budgets for 16 climate zones, so prescriptive values differ by zone. For example, the maximum window U-factor is 0.27 in some zones and 0.30 in others (Table 150.1-A). One zone for the whole tract means one set of values to specify, buy and inspect.

Pairing it with one model for many facings

The zone rule can be combined with the multiple orientation alternative. The performance model is then run facing north, east, south and west, and one CF1R carries all four results for each unique or reversed plan. In the ECC registry the houses of a master plan are tied back to that CF1R, and the plans examiner confirms that every facing passes.

What each house still needs

• Its own CF2R and CF3R, since installation and verification belong to the actual dwelling.
• Solar-ready provisions where they apply. Section 110.10(a)1 covers single-family homes in subdivisions of ten or more that do not have a photovoltaic system installed.

The exception changes only the design target, so confirm details with your plans examiner. Read reusing a Title 24 report for model homes, Title 24 for builders and developers. See solar-ready requirements; a residential report is prepared per plan.

More Title 24 Guides

1. What Every California Homeowner Should Know About Title 24
2. 12 Things to Know Before Ordering a Title 24 Report
3. Title 24 Checklist: What to Have Ready Before You Order
4. How to Read Your CF1R, Page by Page
5. 15 Title 24 Mistakes That Trigger Plan Check Corrections
6. How to Choose a Title 24 Consultant

Frequently Asked Questions

Does a 50/50 split qualify?

Does this let an individual lot in a different zone use the majority zone?

Explore Who Needs Title 24?

1. What Every California Homeowner Should Know About Title 24
2. Title 24 Reports for Homeowners
3. Title 24 for HVAC Contractors
4. Title 24 for Property Managers
5. Title 24 for Solar Installers

View all Who Needs Title 24? guides → · Title 24 Guide · Title 24 guide