7.3 Blower-Door Testing, ACH50 Limits & Dwelling-Unit Alternatives (R402.4.1.2–R402.4.1.3)

7.3 Blower-Door Testing, ACH50 Limits & Dwelling-Unit Alternatives (R402.4.1.2–R402.4.1.3)

Quick Answer: The building or dwelling unit shall be tested. For any compliance path, leakage shall not exceed 5.0 ACH50 or 0.28 cfm/ft² of dwelling-unit enclosure area. Test per ANSI/RESNET/ICC 380, ASTM E779, or ASTM E1827 at 0.2 inch w.g. (50 Pa). On the R401.2.1 prescriptive path, R402.4.1.3 then requires 5.0 ACH in Climate Zones 0, 1, and 2 and 3.0 ACH in Climate Zones 3 through 8. Attached dwelling units and buildings or units 1,500 square feet or smaller may use 0.30 cfm/ft² of enclosure area at 50 Pa in all climate zones.

Table R402.4.1.1 is the visual checklist. R402.4.1.2 is the number that proves the envelope was actually closed. Independent OpenExamPrep material for ICC Exam 79 treats the 2021 first-printing test rules as national IECC text, not a state energy-subcode overlay.

Who must test, and when

The building or dwelling unit shall be tested for air leakage. Testing shall be performed at any time after creation of all penetrations of the building thermal envelope have been sealed. A mid-drywall test that leaves later plumbing, electrical, or range-hood penetrations open is too early. Where required by the code official, testing shall be conducted by an approved third party. A written report of the results shall be signed by the party conducting the test and provided to the code official.

The any-path cap (R402.4.1.2)

The maximum air leakage rate for any building or dwelling unit under any compliance path shall not exceed:

• 5.0 air changes per hour, or
• 0.28 cubic feet per minute per square foot of dwelling unit enclosure area.

Reported pressure is 0.2 inch water gauge (50 Pascals). That is why inspectors say ACH50 even though R402.4.1.3 writes "air changes per hour" — the test method in R402.4.1.2 is a 50 Pa test.

Dwelling unit enclosure area is the surface area of the unit's enclosure, not conditioned floor area. Using CFA in the denominator makes a large ranch look tighter than it is and a two-story townhouse look leakier than it is. The 0.28 cfm/ft² option is useful for attached housing where ACH50 is driven by shared walls, but it is still an any-path alternative to 5.0 ACH50, not a free pass on the prescriptive 3.0 ACH rule in Section R402.4.1.3.

The 5.0 ACH any-path cap is the backstop. The prescriptive 3.0 ACH target in cold climates is tighter. Meeting 5.0 ACH50 does not finish a Climate Zone 5 house on R401.2.1.

Field scenario: Climate Zone 5 house at 4.2 ACH50 on the prescriptive path

A detached Climate Zone 5 house uses Section R401.2.1 (prescriptive R401 through R404). The rater reports 4.2 ACH50. That result is under the any-path 5.0 ACH50 cap, so R402.4.1.2's backstop is met. It is not under the 3.0 ACH cap in R402.4.1.3 for Climate Zones 3 through 8. The house fails prescriptive air leakage.

What can change the outcome:

• Seal the remaining leaks and retest to 3.0 ACH50 or less.
• Switch the project to a path that is not R401.2.1, still staying at or under the 5.0 ACH50 or 0.28 cfm/ft² any-path cap (performance, ERI, or tropical, each with its own additional rules).
• The 0.30 cfm/ft² dwelling-unit alternative does not apply to this detached house unless the building or dwelling unit is 1,500 square feet or smaller.

A 4.2 ACH50 result on a Climate Zone 1 prescriptive house would pass R402.4.1.3, because Climate Zones 0–2 keep the 5.0 ACH prescriptive number.

During testing — the protocol list

R402.4.1.2 tells the tester how to set the house. Teach this list; exam items copy it.

1. Exterior windows and doors, fireplace and stove doors shall be closed, but not sealed, beyond the intended weatherstripping or other infiltration control measures.
2. Dampers including exhaust, intake, makeup air, backdraft, and flue dampers shall be closed, but not sealed beyond intended infiltration control measures.
3. Interior doors, where installed at the time of the test, shall be open.
4. Exterior or interior terminations for continuous ventilation systems shall be sealed.
5. Heating and cooling systems, where installed at the time of the test, shall be turned off.
6. Supply and return registers, where installed at the time of the test, shall be fully open.

Taping extra plastic over windows, foaming a damper shut for the test, closing bedroom doors, leaving an ERV termination open, running the air handler, or shutting registers are all protocol fails. The test is supposed to measure the building as it will operate, with only the continuous-ventilation terminations temporarily sealed so those designed openings do not dominate the reading.

Heated private-garage exception

Exception to the tightness test: for heated, attached private garages and heated, detached private garages accessory to one- and two-family dwellings and townhouses not more than three stories above grade plane, building envelope tightness and insulation installation shall be considered acceptable where the items in Table R402.4.1.1, applicable to the method of construction, are field verified. Where required by the code official, an approved third party independent from the installer shall inspect both air-barrier and insulation-installation criteria. The heated garage space shall be thermally isolated from all other habitable, conditioned spaces in accordance with R402.2.12 and R402.3.5, as applicable.

This exception is for the garage, not a free skip of the dwelling's blower-door test. Isolation, Table R402.4.1.1 verification, and the 1–2 family / townhouse / three-story limit all have to be true.

Dwelling-unit alternative (0.30 cfm/ft²)

When testing individual dwelling units, an air leakage rate not exceeding 0.30 cfm/ft² of dwelling unit enclosure area, tested to the same standards and reported at 0.2 inch w.g. (50 Pa), shall be permitted in all climate zones for:

1. Attached single- and multiple-family building dwelling units, and
2. Buildings or dwelling units that are 1,500 square feet (139.4 m²) or smaller.

Do not mix 0.28 (any-path enclosure option) with 0.30 (this attached / small-unit alternative). The 0.30 option is slightly leakier on a cfm/ft² basis and exists because attached units share walls and small units have a high surface-to-volume ratio that makes ACH50 harsh.

Mechanical ventilation

R402.4.1.2 closes by requiring mechanical ventilation in accordance with IRC Section M1505 or IMC Section 403.3.2, as applicable, or other approved means. A tighter house still needs outdoor air. R403.6 repeats that buildings complying with R402.4.1 shall be ventilated to those same sections, with automatic or gravity dampers on outdoor-air intakes and exhausts. Fan efficacy and airflow testing are Chapter 8; the air-leakage chapter's job is to remember that the tightness test does not delete ventilation.

Plans-examiner checklist

1. Which R401.2 path is on the energy forms? If R401.2.1, write 5.0 ACH (CZ 0–2) or 3.0 ACH (CZ 3–8) on the inspection card, not only 5.0.
2. Is the project attached or ≤ 1,500 ft²? Then 0.30 cfm/ft² of enclosure is available.
3. Require the signed report, the standard used (380 / E779 / E1827), and the 50 Pa result.
4. Reject a test performed before envelope penetrations were sealed, or a protocol that extra-sealed windows or closed interior doors.

Independent OpenExamPrep study material for Exam 79 treats 4.2 ACH50 in Climate Zone 5 on the prescriptive path as a fail, even though it is under 5.0.