How Much Compliance Margin Should I Keep Before Construction?
The code needs zero or better, and it names no larger target. The right cushion is whatever covers the substitutions you expect: a different window, a swapped unit, thinner insulation. A zero-margin design has no room, so any change that lowers a modelled input can turn the result negative and send amended documents to the building department.
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Why zero is a thin place to stand
Section 150.1(b) only asks that the proposed design use no more energy than the standard design. A design sitting at exactly zero passes, and it also fails the moment one input is made worse. The code does not say how much room to leave, so decide before materials are ordered.
What eats margin
- Windows: a higher U-factor or SHGC, or a window moved to another wall.
- Equipment: a unit with a lower rating than the one modelled.
- Insulation: a different R-value or installation method.
- Orientation: a rotated plan. A design checked in several orientations must comply in every one.
What happens when a change is made
If a specification changes before final construction so the building may no longer comply, the building must be brought back into compliance, with amended plans, specifications and certificates submitted for approval. The manual sorts changes into clear and doubtful: swapping a single-glazed metal window for a high-performance double-pane vinyl one is a clear-cut downgrade, while a change of orientation or window location may be hard to judge. The installer's certificate declares the installation matches the approved plans, so a substitution is caught at the CF2R and at inspection. After the fact the steps are on the installer-equipment page and the architect-change page.
Re-runs can land on new values
Rule updates come no more than twice a year, in January and July, and a previous version expires 60 to 90 days after a new one is approved. A re-run months later may use different values than the original, which a thin margin cannot absorb.
How to hold a margin cheaply
- Ask your consultant for a what-if run before ordering windows or equipment, using the two or three substitutes you expect.
- Fix the items that cost little to improve at design stage, not on site.
- Put the modelled values on the schedules so installers know what not to change.
See what the margin number means and what revisions are included. Orders start on the residential report page.
Common Title 24 Questions
- What is Title 24?
- Do I need a Title 24 report?
- How much does a Title 24 report cost?
- How long does a Title 24 report take?
- What is included in a Title 24 report?
- What plans do I need to upload?
Frequently Asked Questions
It complies, but any later change that lowers a modelled input can push it below zero. Ask for a what-if run if substitutions are likely.
No. Part 6 requires that the proposed design not exceed the standard design budget.
Explore Performance Calculations
- 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
- Which Title 24 Performance Credits Need an ECC-Rater Test?
- Why Did My Project Fail Title 24? How to Read a Failing Result
View all Performance Calculations guides → · Reports and Calculations · Title 24 guide