Re-Siding a House: Does Title 24 Require Wall Insulation?
The Standards do not name re-siding as a trigger for wall insulation. Section 150.2(b)1 sends an altered component to Section 150.0(c), so the question is whether the wall itself is altered, not just its covering. If it is, the minimum is U-0.095 in 2x4 framing or U-0.069 in 2x6. The building department decides how it treats the permit.
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Where Part 6 mentions siding
In the single-family Standards, siding appears only in the addition rules. An existing wood-framed wall whose siding is not being removed or replaced takes cavity insulation alone, R-15 in 2x4 framing and R-21 in 2x6, with no continuous layer (Sections 150.2(a)1Aiv and 1Bvi). Take the siding off such a wall and that allowance stops applying. Section 150.2(b), the alterations rule, never names siding, and the Standards set no requirement on the cladding material.
When the wall itself is altered
Insulation added or replaced in the cavity, or framing rebuilt, makes the wall an altered component. It must meet Section 150.0(c): U-0.095 in 2x4 framing, which R-15 at 16 inches on center achieves, or U-0.069 in 2x6, which R-21 achieves. An existing 2x4 wall already at R-11 or U-0.110 is excepted. The manual's alterations table words the item as adding exterior framed wall insulation.
Foam behind the new siding
The manual notes that rigid insulation may be integral to siding, and the residential code has fastener rules for exterior foam in Section R703.15. JA4 Table 4.3.1 shows what a layer buys: R-5 continuous over a 2x6 wall with R-21 reaches U-0.048, the new-home figure. That is a target for new homes, not a demand on an old one. A performance model credits such an upgrade only against the Table 150.2-G baseline, which is the mandatory value unless an ECC-Rater verifies the existing wall.
Windows are the usual catch
If windows are replaced during the job, replacement glazing falls under Section 150.2(b)1B. Up to 75 square feet of vertical replacement glass may meet U-0.40, and SHGC 0.35 in zones 2, 4 and 6 to 15. Glass replaced in an existing sash and frame is a repair if it performs at least as well as the original. More is on window Title 24.
Next steps
Wall assemblies are compared on wall insulation. The plaster-and-lath case is re-stuccoing a house, and whole-house scope is on remodel Title 24. Order from residential Title 24 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
The building department decides. Whether a permit and an energy certificate are needed depends on the scope it sees, so ask before the siding comes off.
It can in a performance model, but credit is measured against a baseline set by Table 150.2-G. Without verification of the existing wall the baseline is the mandatory minimum.
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