Prescriptive vs Performance Compliance for Home Additions
Prescriptive means meeting every applicable item of Section 150.2(a)1 for the addition and filing CF1R-ADD-01-E, ADD-02-E or, at 1,000 square feet and over, CF1R-NCB-01-E. Performance means modeling and filing CF1R-PRF-01-E. One failing item, such as glass area, sends the project to performance.
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The prescriptive side
Three paths follow the addition's total floor area: 400 square feet or less, over 400 to 700, and over 700. Several separate additions under one permit add together. Under 1,000 square feet the certificate is the CF1R-ADD-01-E, or the CF1R-ADD-02-E when no field verification is needed. At 1,000 or more it is the CF1R-NCB-01-E. All applicable items must be met, or the building complies by performance.
What usually pushes a job to performance
- Glazing over the tier cap, such as more than the greater of 175 square feet or 20 percent in an addition above 700 square feet.
- A cool roof where the addition exceeds 300 square feet; the manual's 450 square foot example says a model can trade it away (Example 9-17).
- Electric baseboard heat in the new room rather than extended ducts (Example 9-37).
- An instantaneous gas heater as a second water heater (Example 9-32).
- A window reused from the old wall that misses the limits (Example 9-10).
Two ways to model it
Addition alone models only the new space and needs little data on the house, but some prescriptive allowances do not carry over and improvements to the existing house cannot be traded. Existing + addition + alteration offers the most flexibility at the cost of plans and data for the old building (how that method works).
Items that never depend on the path
PV is not required for additions under any approach (Example 9-6). Quality insulation installation above 700 square feet is prescriptive, yet it can be traded off in a model (Example 9-8).
The generic comparison is on prescriptive versus performance. Size-specific rules: 300 square feet, 700 square feet and 1,000 square feet. Forms: residential CF1R. Order from residential reports.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
It usually involves less modeling, but one item that cannot be met forces the performance path. The right route is whichever lets the design be approved as drawn.
Under 1,000 square feet, the CF1R-ADD-01-E, or the CF1R-ADD-02-E if no field verification is required. At 1,000 square feet or more it is the CF1R-NCB-01-E.
Explore Performance Calculations
- Prescriptive vs Performance Compliance
- How Much Compliance Margin Should I Keep Before Construction?
- Title 24 Trade-Offs: A Worked Example of What Can and Cannot Move
- What Does Compliance Margin Mean on a Title 24 Report?
- What Is the Title 24 Energy Budget? LSC, Source Energy and the Old TDV
View all Performance Calculations guides → · Reports and Calculations · Title 24 guide