Burying Attic Ducts Under Blown-In Insulation: What Title 24 Says
Burying attic ducts under blown insulation is a performance-method compliance credit, not a prescriptive shortcut. Ducts designed to be buried need R-4.2 or more, vertical markers at least every 8 feet and a warning sign at the attic access, and the layout is verified before the ducts are covered.
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Two credits, one set of marker rules
Appendix RA3.1.4.1.5 covers buried ducts on the ceiling and RA3.1.4.1.6 covers deeply buried ducts. Both use the same field requirements:
- Ducts designed to be buried are insulated to R-4.2 or greater.
- Ducts designed to touch the ceiling sit no more than 3.5 inches from the drywall.
- A sign near the attic access reads "Caution: Buried Ducts. Markers indicate location of buried ducts."
- Completely buried ducts carry vertical markers visible after the insulation goes in, at least every 8 feet and at the start and end of each run.
Verification comes before the insulation
An ECC-Rater inspects before the ducts are covered, confirming that the installed layout matches the Duct Design Layout. That layout is a prerequisite: it goes in with the building plans and the registered compliance document, the enforcement agency approves it, and a copy stays available on site. Deviations need a revised layout approved by the agency.
Sealing and QII ride along
Table RA2-1 states that for buried duct measures, duct sealing and High Quality Insulation Installation are required. The sealing side is covered in duct leakage testing, and the insulation side in quality insulation installation.
Why it is not a prescriptive route
The credit appears in the performance method. Exception 2 to Section 150.0(a)1 lets ducts buried within insulation in an attic that complies through Section 150.1(b), verified per RA3.1.4.1, skip the roof deck rule that otherwise requires U-0.184 in newly constructed attics above conditioned space in zones 4 and 8 to 16. The two routes are compared in prescriptive versus performance.
A caution for retrofits
On the prescriptive path, new ducts in unconditioned space in an alteration still follow Table 150.2-D, R-6 or R-8 by zone (Section 150.2(b)1Di). Burying is not a way around that table. For the values, see duct insulation, and for ducts kept out of the attic altogether, ducts in conditioned space. New builds start at new home Title 24.
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
The buried-duct requirements are written as a verified compliance credit with a design layout and a pre-cover inspection. Check with your report preparer and building department before relying on it for an existing house.
"Caution: Buried Ducts. Markers indicate location of buried ducts." It hangs near the attic access.
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View all Ducts guides → · HVAC and Water Heating · Title 24 guide