Brick, Block and Concrete Walls: Mass Wall Insulation Under Title 24
Walls with a heat capacity of at least 7.0 are mass walls and follow their own rows of Table 150.1-A, not the R-15 and R-21 stud-wall shortcut. You meet the row either with an assembly U-factor or with continuous insulation of at least the tabulated R-value, on the inside face or the outside face.
- Choose your report
- Upload your plans
- Pay securely
- Permit-ready report by email
Does your wall count as mass?
The test is heat capacity, written in footnote 5 of Table 150.1-A as 7.0 or more. Appendix JA4 carries thermal mass data for masonry and concrete assemblies. The mandatory rule in Section 150.0(c) sends mass and masonry walls to Table 150.1-A, and caps an opaque non-framed assembly that is not mass at U-0.102. Other unframed walls that are not mass use the framed-wall values.
Two ways to pass, and which face
Section 150.1(c)1B lets a mass wall meet the table by its assembly U-factor or by continuous insulation with an R-value at least equal to the table. "Interior" means the layer sits on the inside surface and "exterior" on the outside. Above grade in zones 1 to 15, the table reads U-0.077 or R-13 inside, and U-0.125 or R-8 outside. Zone 16 is tighter: U-0.059 or R-17 inside, U-0.077 or R-13 outside.
Below grade
- Interior: R-13 in zones 1 to 15, with R-15 in zone 16.
- Exterior: R-5 in zones 1 to 13, R-10 in zones 14 and 15, and R-19 in zone 16.
Adding a layer to an existing wall
Appendix JA4 supplies the base U-factors for the wall in Tables 4.3.5 to 4.3.7. Table 4.3.14 gives the effective R-value of an added inside or outside layer. A system that is only insulation, such as EIFS, uses row 26 of that table.
The air barrier and QII
Quality insulation installation applies to non-framed walls, and its definition names masonry, concrete and concrete sandwich panels. Fully grouted block, cast-in-place or precast concrete and 5/8-inch Portland cement parge or gypsum plaster all count as air barrier materials. The rater verification and paperwork still apply.
Framed walls are on wall insulation and, for secondary units, ADU wall insulation. Read quality insulation installation, re-stuccoing and air barrier requirements. A residential report models the mass wall type you choose.
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
It depends on heat capacity, which is the test in the table footnote. Both are non-framed assemblies; one that is not mass must reach U-0.102.
Yes. The table gives separate exterior values, and exterior insulation may be met by U-factor or by continuous R-value.
Explore Walls
- Insulating the Wall Between the House and an Attached Garage
- Kneewall Insulation Under Title 24: R-Value, Air Barrier and What QII Checks
- QII Hard-to-Insulate Spots: Corners, Tub Walls, Bump-Outs and Steel Framing
- Window and Door Header Insulation: R-3, R-5 and the Four QII Header Designs
- Commercial Air Barrier Under Title 24: The 25 Percent Wall Alteration Rule
View all Walls guides → · Windows and Building Envelope · Title 24 guide