Air Sealing and the Air Barrier: What Title 24 Requires in a House
Section 110.7 requires every joint, penetration and opening in the building envelope that can leak to be caulked, gasketed, weather-stripped or otherwise sealed. It applies to new construction, additions and altered components. An air barrier is a continuous set of joined, sealed materials that passes one of three leakage tests.
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The one mandatory sentence
Section 110.7 reads, in effect: all joints, penetrations and other openings in the envelope that are potential sources of air leakage shall be sealed to limit infiltration and exfiltration. No product or leakage number is attached to the sentence. It reaches additions through Section 150.2(a) and altered components through Section 150.2(b)1.
What counts as an air barrier
The definition in Section 100.1 and Appendix RA3.5.2 describes interconnected materials and assemblies joined and sealed to form a continuous barrier between conditioned and unconditioned space. It must pass one of three tests:
- Individual materials with air permeance of 0.004 cfm per square foot or less at 75 Pa (ASTM E2178).
- Assemblies averaging 0.04 cfm per square foot or less at 75 Pa.
- A completed building tested at 0.40 cfm per square foot or less at 75 Pa.
Materials that qualify
The appendix lists plywood or OSB at least 3/8 inch, 1/2-inch gypsum board, cement board and particleboard, 1/2-inch XPS or foil-faced polyisocyanurate, closed-cell spray foam at least 2 inches thick, open-cell foam at least 5-1/2 inches, built-up and modified bitumen membranes, 5/8-inch parge or plaster, concrete, fully grouted block, and sheet steel or aluminum. Each counts only when installed to the manufacturer's instructions with joints sealed.
Where a remodel must seal
- An altered vented attic with under R-19 existing: all accessible ceiling-plane areas are air sealed in zones 2, 4 and 8 to 16, except where atmospherically vented combustion appliances sit inside the pressure boundary.
- New and replacement windows must be caulked and sealed around the frame; field-fabricated windows and doors must also be weatherstripped, with unframed glass doors and fire doors excepted.
Where QII adds a step
Under quality insulation installation the air barrier must enclose the whole building and be verified by the ECC-Rater before insulation goes in, with product data sheets and installation guidelines on file. A leakage test is a separate matter, covered in the blower door page.
Related: quality insulation installation, attic insulation for remodels, the attic hatch and re-stuccoing. See our 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
Caulk seals joints. The barrier itself is the material or assembly that passes a leakage test, such as sheathing, gypsum board or plaster, with its joints sealed.
No for the attic ceiling rule. Exception 1 to Section 150.2(b)1Jii excuses dwelling units with at least R-19 existing. Section 110.7 still applies to any altered component.
Explore Insulation
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- Attic Hatch Insulation and Gasket: What Title 24 Requires
- Attic Insulation Certificate: What the Contractor Must Give You
- Attic Insulation Requirements for California Remodels
View all Insulation guides → · Windows and Building Envelope · Title 24 guide