24 CFR § 3280.502 - Definitions.

---
identifier: "/us/cfr/t24/s3280.502"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "24 CFR § 3280.502 - Definitions."
title_number: 24
title_name: "Housing and Urban Development"
section_number: "3280.502"
section_name: "Definitions."
chapter_name: "OFFICE OF ASSISTANT SECRETARY FOR HOUSING—FEDERAL HOUSING COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT"
part_number: "3280"
part_name: "MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "15 U.S.C. 2697, 42 U.S.C. 3535(d), 5403, and 5424."
regulatory_source: "40 FR 58752, Dec. 18, 1975, unless otherwise noted. Redesignated at 44 FR 20679, Apr. 6, 1979."
cfr_part: "3280"
---


# 3280.502 Definitions.

(a) The following definitions are applicable to subpart F only:

(1) *Pressure envelope* means that primary air barrier surrounding the living space which serves to limit air leakage. In construction using ventilated cavities, the pressure envelope is the interior skin.

(2) *Thermal envelope area* means the sum of the surface areas of outside walls, ceiling and floor, including all openings. The wall area is measured by multiplying outside wall lengths by the inside wall height from floor to ceiling. The floor and ceiling areas are considered as horizontal surfaces using exterior width and length.