QII Hard-to-Insulate Spots: Corners, Tub Walls, Bump-Outs and Steel Framing
QII gives seven awkward wall spots their own rules: stud corners, tub and shower walls, double walls, structural steel, equipment closets, pipes in cold zones, wiring. Most of them must be insulated before the tub enclosure, sheathing or lath is installed, because afterward nobody can reach the cavity.
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Before the tub goes in
Corner channels, wall intersections and the cavity behind a tub or shower enclosure must reach the proper R-value, and the appendix admits this can usually be done only before the enclosure, the exterior sheathing or the stucco lath goes on. An air barrier also goes on the inside of the exterior wall next to the tub or shower. The manual tells the inspector to look behind obstructions such as a bathtub at the insulation visit.
Gaps too small for a batt
Spaces under 2 inches wide, such as corners and partition-to-exterior intersections, are filled with snugly fitted insulation or minimally expansive foam. At window and door jambs the limit drops to 1 inch.
Double walls and bump-outs
Insulation fills the whole cavity, or an extra air barrier goes inside and touches the insulation so it fills the cavity formed. The entire double wall or framed bump-out must be airtight.
Structural steel, bracing and tie-downs
These must be identified on the plans with diagrams. Insulation limits thermal bridging and encloses or adheres to all sides and ends of the structural framing that divides conditioned from unconditioned space, and the structural parts are airtight.
Equipment closets
Walls of closets for HVAC or water heating equipment that needs combustion air are insulated at least like demising walls, such as the wall to an attached garage.
Pipes and wiring
Batts are cut or split around wiring and plumbing, with compression limited to 30 percent of nominal thickness, and insulation is placed behind electrical boxes that are shallower than the cavity. In zones 2, 11 to 14 and 16, where water pipes may freeze, at least half of a batt installation goes between the pipe and the outside surface. The spray foam version asks for two thirds, in zones 14 and 16.
The general method is on quality insulation installation. Related details: headers, rim joists and kneewalls. For wall values see wall insulation, or order a residential report.
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
They apply where QII applies: new homes and additions over 700 square feet. A performance model can trade QII away.
Several spots are unreachable after the tub, sheathing or lath is installed, so the insulation has to be in and seen first.
Explore Walls
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- Commercial Air Barrier Under Title 24: The 25 Percent Wall Alteration Rule
- Advanced Framing and 24-Inch Stud Spacing: How Title 24 Counts Wall Insulation
- Brick, Block and Concrete Walls: Mass Wall Insulation Under Title 24
- Insulating the Wall Between the House and an Attached Garage
View all Walls guides → · Windows and Building Envelope · Title 24 guide