Crawl Space Insulation Requirements Under Title 24

Which crawl space do you have

With ordinary vents, the floor above is insulated like any raised floor, R-19 between the joists. A controlled-ventilation or unvented crawl space can take a different route, in which the walls around the crawl space are insulated instead of the floor above it.

The four conditions for omitting floor insulation

1. The foundation walls are insulated to the wall minimums in Table 150.1-A.
2. A Class I or Class II vapor retarder covers the entire crawl space floor.
3. Vents to the outside have automatically operated, temperature-actuated louvers.
4. The criteria in Residential Appendix RA4.5.1 are met.

Section 150.0(d) and Section 150.1(c)1C carry the same conditions, so the route works under the mandatory and prescriptive rules alike.

What Appendix RA4.5.1 adds

• The dampers must be shown on the plans, fully closed at about 40 degrees Fahrenheit and fully open at about 70.
• Vent area is reasonably distributed between opposing foundation walls for cross ventilation.
• Foam touching the earth must be closed-cell and water resistant, meeting the 0.3 percent absorption and 2.0 perm per inch limits that apply to slab edge insulation.
• Eligibility is at the enforcement officials' discretion. Where the site has drainage doubts, the applicant must prove the drainage will work.

The vapor retarder is not optional

Section 150.0(g)1 requires a Class I or II retarder over the earth floor of an unvented crawl space in all 16 zones, and extends the same rule to a controlled-ventilation crawl space that uses the exception.

When you are altering, not building

The manual's alterations table lists adding raised floor insulation at R-19 or an equivalent U-factor, with the exception for floors over controlled-ventilation or unvented crawl spaces. The floor itself is covered on raised floor insulation, and the full package on insulation requirements. Lower-level conversions are on basement conversions. Our residential Title 24 reports start from the plans.

Common Title 24 Questions

1. When is Title 24 required for a home?
2. Does a remodel need Title 24?
3. Does a room addition need Title 24?
4. What plans are needed for a residential Title 24 report?
5. How much does a residential Title 24 report cost?
6. How long does a residential Title 24 report take?

Frequently Asked Questions

Does a crawl space with ordinary vents need floor insulation?

Who decides whether my site qualifies?

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