6.3 Fenestration Air Leakage, Opaque Doors & Replacement Units (R402.4.3, R503.1.1.1)

6.3 Fenestration Air Leakage, Opaque Doors & Replacement Units (R402.4.3, R503.1.1.1)

Quick Answer: Windows, skylights, and sliding glass doors: air infiltration ≤ 0.3 cfm/ft². Swinging doors: ≤ 0.5 cfm/ft². Test to NFRC 400 or AAMA/WDMA/CSA 101/I.S.2/A440 by an accredited independent laboratory; list and label. Site-built windows, skylights, and doors are excepted. Replacement units that include sash and glazing shall meet Table R402.1.3 U-factor and SHGC; more than one replacement unit may use an area-weighted average. Glass-only replacements in an existing sash and frame are repairs (R504.2), not that replacement rule.

A tight NFRC U-factor on a leaky slider still fails the envelope. Independent OpenExamPrep material for Exam 79 splits the job: Section 6.1 rated U-factor and SHGC, Section 6.2 averaged them, and this section checks air leakage of the product, opaque swinging doors, R402.5 tradeoff caps, and existing-building replacements. National 2021 IECC residential provisions, not a state overlay.

R402.4.3 — fenestration air leakage

Windows, skylights, and sliding glass doors shall have an air infiltration rate of not greater than 0.3 cfm per square foot (1.5 L/s·m²), and for swinging doors, not greater than 0.5 cfm per square foot (2.6 L/s·m²), when tested in accordance with NFRC 400 or AAMA/WDMA/CSA 101/I.S.2/A440 by an accredited, independent laboratory and listed and labeled by the manufacturer.

0.3 versus 0.5 is the first trap. Sliding glass doors travel with windows and skylights at 0.3. Side-hinged swinging doors — including opaque entry doors — are allowed 0.5. Do not fail a swinging door for 0.4 cfm/ft², and do not pass a slider at 0.5 because “it is a door.”

cfm per square foot of fenestration is not ACH50 and is not the 0.28 or 0.30 cfm/ft² enclosure leakage in R402.4.1.2. Chapter 7 will test the blower door. This section tests the product label.

Who tests. An accredited independent laboratory. The manufacturer then lists and labels. A contractor fog test on the jobsite is not NFRC 400. AAMA/WDMA/CSA 101/I.S.2/A440 is the other listed standard — remember the full designation; “AAMA” alone is a weak exam answer.

Exception: site-built windows, skylights, and doors. Site-built units are not required to carry the R402.4.3 NFRC 400 / AAMA listing. They are still fenestration for U-factor and SHGC (NFRC 100/200 or defaults), and the rough-opening seal in Table R402.4.1.1 still applies: the space between framing and skylights, and the jambs of windows and doors, shall be sealed. Product leakage listing and jamb air sealing are different rows on the inspection.

Opaque swinging doors. Treat them as fenestration products. They need a U-factor (NFRC 100 or Table R303.1.3(2) default) unless R402.3.4 exempts one ≤ 24 ft² assembly from the R402.1.2 U-factor — that exemption does not erase R402.4.3. A 20 ft² side-hinged opaque door can skip the 0.30 U-factor on the R402.1.2 path and still must meet 0.5 cfm/ft² if it is a factory swinging door subject to R402.4.3. Sliding glass doors never use the 24 ft² opaque exemption and never use the 0.5 cfm/ft² swinging-door rate.

R402.5 — tradeoff caps, reinforced

Chapter 3 taught Total UA. Repeat the backstop here because glazing items will try to spend extra wall insulation on terrible glass.

The area-weighted average maximum fenestration U-factor permitted using tradeoffs from R402.1.5 or R405 shall be:

• 0.48 in Climate Zones 4 and 5 for vertical fenestration
• 0.40 in Climate Zones 6 through 8 for vertical fenestration
• 0.75 in Climate Zones 4 through 8 for skylights

The area-weighted average maximum fenestration SHGC permitted using tradeoffs from R405 in Climate Zones 0 through 3 shall be 0.40.

That SHGC 0.40 cap is an R405 tradeoff cap, not a Total UA SHGC holiday. On R402.1.5, SHGC still comes from Table R402.1.2 (0.25 in Climate Zones 0–3; 0.40 in Climate Zone 4 except Marine; NR for Climate Zone 5 and Marine 4 on that table). Exception: the R402.5 maxima shall not be required in storm shelters complying with ICC 500. That is not a sunroom exception.

A Climate Zone 5 UA worksheet that averages vertical glass to U-0.50 fails 0.48 even if ceiling UA more than pays for it. A Climate Zone 7 worksheet that averages vertical glass to U-0.45 fails 0.40.

R503.1.1.1 — replacement fenestration

Existing-building Chapter 5 is a 16 percent domain. This section plants the window-specific rule; Chapter 12 will place it among additions, alterations, and repairs.

R503.1.1.1 Replacement Fenestration. Where some or all of an existing fenestration unit is replaced with a new fenestration product, including sash and glazing, the replacement fenestration unit shall meet the applicable requirements for U-factor and SHGC as specified in Table R402.1.3. Where more than one replacement fenestration unit is to be installed, an area-weighted average of the U-factor, SHGC, or both of all replacement fenestration units shall be an alternative that can be used to show compliance.

Table R402.1.3, not Table R402.1.2. New construction may have declared the U-factor table. Replacements are sent to the R-value table’s fenestration columns. That swap changes SHGC in Climate Zone 5: Table R402.1.2 lists SHGC NR for Climate Zone 5 and Marine 4, but Table R402.1.3 lists 0.40. A Climate Zone 5 replacement window with SHGC 0.50 fails R503.1.1.1 even if a new house next door on Table R402.1.2 would have seen NR. Climate Zones 0–1 replacements still see Fen U NR on Table R402.1.3, with SHGC 0.25 and skylight U 0.75 still in force.

More than one unit. Average U-factor, SHGC, or both across the replacement units. Do not average new replacement glass with remaining original 1970s aluminum singles that are staying in place. The average is among the units being installed.

Trigger: sash and glazing. New product including sash and glazing is a replacement unit. Pulling the old vinyl frame and installing a new framed window is R503.1.1.1.

Glass-only work is a repair

R504.2 lists what this code considers repairs. Item 1 is glass-only replacements in an existing sash and frame. That work is not R503.1.1.1. Do not require a Table R402.1.3 U-factor and SHGC showing for a broken insulated-glass unit slipped back into the original sash. (Other codes and the contract still care about safety glazing; Exam 79 energy items care about the repair-versus-replacement split.)

R503.1.1 also lists alterations that shall not be required to comply with new-construction envelope provisions provided energy use is not increased, including storm windows installed over existing fenestration and surface-applied window film installed on existing single-pane fenestration assemblies to reduce solar heat gain, provided the code does not require the glazing or fenestration assembly to be replaced. Those are not “replacement units” under R503.1.1.1.

R503.1.1 does pull R402.3.1, R402.3.2, and R402.4.3 into alterations. Averaging and product air leakage still matter when new windows are part of an alteration. It does not list R402.3.3 or R402.3.4. Do not give a replacement job the 15 ft² glazed exemption or the 24 ft² opaque-door exemption unless a later existing-building provision actually grants it — R503.1.1.1’s own rule is Table R402.1.3.

Field and plans scenarios

New house, factory slider. NFRC label shows U-0.29, SHGC 0.38, air leakage 0.22 cfm/ft² in Climate Zone 4 except Marine on Table R402.1.3. U-factor and SHGC pass (0.30 and 0.40). Air leakage passes 0.3. Jambs still get sealed per Table R402.4.1.1.

New house, swinging opaque door. NFRC air leakage 0.42 cfm/ft². That is ≤ 0.5, so R402.4.3 passes. U-factor is a separate 0.30 (or 24 ft² exemption, or average) check.

Replacement job, Climate Zone 5. Three new vinyl windows, sash and frame included, SHGC 0.32, 0.38, and 0.45 with equal areas. Table R402.1.3 SHGC is 0.40. The 0.45 unit fails by itself; the three-unit average is (0.32 + 0.38 + 0.45) ÷ 3 = 0.383, which is ≤ 0.40 if areas are equal. Document the areas. Air leakage labels still need 0.3 / 0.5 as applicable.

Repair job. One IG unit replaced in a 1995 aluminum sash. R504.2 repair. Do not write a failed inspection solely because the new pane lacks a whole-unit NFRC 100 U-0.30 label.

Site-built storefront at a dwelling covered by the residential provisions. No R402.4.3 listing is required under the site-built exception. U-factor and SHGC still need a rating or a default, and the perimeter still gets sealed.

Keep this independent: OpenExamPrep teaching of 2021 IECC R402.4.3, R402.5, R503.1.1.1, and R504.2 for Exam 79 study, not an ICC bulletin on existing buildings.