Commercial Air Barrier Under Title 24: The 25 Percent Wall Alteration Rule
New nonresidential buildings need a continuous air barrier designed and detailed on the drawings, and an existing wall where at least 25 percent of the wall area is altered must comply too. Testing is optional; if done, the target is 0.40 cfm per square foot at 75 pascals. The performance method cannot trade the requirement away.
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What the drawings must show
Section 140.3(a)9 asks for a continuous air barrier designed and built to control air leakage into and out of conditioned space. Construction documents must show the barrier boundaries, interconnections and penetrations, with square foot calculations for all sides. Relocatable public school buildings are excepted. The nonresidential manual adds that the requirement cannot be traded off in the performance approach.
What counts as a barrier
The barrier is sealed at all joints and made of one of three things: materials with air permeance of 0.004 cfm per square foot or less, assemblies averaging 0.04 or less, or materials Table 140.3-A deems to comply. The table includes 3/8-inch plywood or oriented strand board, 1/2-inch gypsum board, 2 inches of closed-cell spray foam at 2.0 pcf, cast-in-place concrete and fully grouted concrete block. Painted or sealed concrete masonry and structural insulated panels are deemed assemblies.
Testing: optional, with consequences
Verification of the installed barrier "may be performed." If it is, the whole building must test at 0.40 cfm per square foot or less at 75 pascals, with a sectional method for buildings over 50,000 square feet of conditioned floor area. A miss triggers a visual inspection and diagnostic evaluation, sealing of observed leaks wherever that can be done without destroying existing components, and a retest if the first result exceeded 0.6.
The 25 percent trigger in alterations
Section 141.0(b)2Q applies the air barrier requirement to an existing wall where at least 25 percent of the wall area is being altered. Healthcare facilities are excepted. The Standards do not explain how altered area is counted, so ask the building department before you size the scope, and keep the wall-area arithmetic in your submittal.
Homes handle this differently
A house gets its air sealing through Section 110.7 and QII, explained at quality insulation installation. Commercial wall values are on commercial wall insulation, additions are on commercial additions, and the alteration versus new-build split is on alterations versus new construction. For a quote, start at commercial Title 24.
Common Title 24 Questions
- When does a commercial project need Title 24?
- Does an office tenant improvement need Title 24?
- Does a restaurant remodel need Title 24?
- Does a retail tenant improvement need Title 24?
- What plans are needed for a commercial Title 24 report?
- What is an NRCC certificate of compliance?
Frequently Asked Questions
No. The Standards say verification of the installed air barrier may be performed. If it is, the 0.40 cfm per square foot target applies to the whole building.
Only if at least 25 percent of an existing wall area is altered. The department decides how that area is measured.
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