12.2 Alterations, Replacement Fenestration & Repairs (R503, R504)

12.2 Alterations, Replacement Fenestration & Repairs (R503, R504)

Quick Answer: R503.1 requires alterations to comply with new-construction requirements without forcing unaltered portions to comply. The existing building shall not be less conforming than it was, shall not be made unsafe or overloaded, and shall not use more energy than it did before the alteration. Envelope assemblies that are part of the alteration follow R402.1.2 or R402.1.3, R402.2.1–R402.2.12, R402.3.1, R402.3.2, R402.4.3, and R402.4.5, unless a listed exception applies and energy use is not increased. Replacement fenestration that includes sash and glazing shall meet U-factor and SHGC in Table R402.1.3; multiple units may use an area-weighted average. R504 keeps true repairs — including glass-only replacements in an existing sash and frame — out of the alteration rules. Lighting alterations that replace less than 10 percent of the luminaires in a space are excepted from R404.1 if installed interior lighting power does not increase.

This section is the rest of the 10 percent Exam 79 task on conditioned-space additions, alterations, repairs, and window replacements. Independent OpenExamPrep material for ICC Exam 79 uses the 2021 IECC residential provisions (first printing). Do not import a state's energy-subcode amendments from a public viewer.

R503.1 general alteration rules

Alterations to any building or structure shall comply with the requirements of the code for new construction, without requiring the unaltered portions of the existing building or building system to comply. Alterations shall be such that the existing building or structure is not less conforming to this code than it was prior to the alteration.

Two more limits sit in the same section. Alterations shall not create an unsafe or hazardous condition or overload existing building systems. Alterations shall be such that the existing building or structure does not use more energy than it did prior to the alteration. Replacing R-38 attic insulation with R-19 because the contractor had leftovers fails that last sentence even if no table was opened.

Alterations to existing buildings shall comply with R503.1.1 through R503.1.4 — envelope, heating and cooling ducts, service hot water, and lighting.

Do not confuse this charging language with R502. An addition adds floor area or systems. A change in space conditioning converts unconditioned or low-energy space to conditioned space and is sent to R502 by R501.2. R503 is for work on assemblies and systems that are already part of the conditioned building, unless a listed exception applies.

R503.1.1 envelope and the six exceptions

Building envelope assemblies that are part of the alteration shall comply with R402.1.2 or R402.1.3, R402.2.1 through R402.2.12, R402.3.1, R402.3.2, R402.4.3, and R402.4.5. That is a tighter list than the addition pointer in R502.3.1. Air-leakage testing (R402.4.1.2) is not in the alteration envelope list. Fenestration U-factor and SHGC still arrive through the tables and through R503.1.1.1.

Then comes the exception. The following alterations shall not be required to comply with the requirements for new construction provided that the energy use of the building is not increased:

1. Storm windows installed over existing fenestration.
2. Existing ceiling, wall, or floor cavities exposed during construction provided that these cavities are filled with insulation.
3. Construction where the existing roof, wall, or floor cavity is not exposed.
4. Roof recover.
5. Roofs without insulation in the cavity and where the sheathing or insulation is exposed during reroofing shall be insulated either above or below the sheathing.
6. 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.

Exception 2 is the field favorite. Opening a 2x4 wall and filling the cavity with insulation satisfies the listed exception. It does not silently require the cavity to reach the Climate Zone 5 wood-frame wall R-value in Table R402.1.3. Leaving the cavity empty after it was opened fails the "filled with insulation" condition, so the exception is lost.

Exception 3 protects work that never opens the cavity: siding overlay, interior paint, a new drywall skin over an unopened wall. Exception 4 roof recover is not the same as tearing the roof down to the sheathing. Exception 5 is the reroofing rule for a roof that had no cavity insulation and whose sheathing or insulation is exposed: insulate above or below the sheathing. That is still a requirement, even though it lives in the exception list. Do not treat exception 5 as permission to recover a bare roof with no insulation.

Exception 1 storm windows and exception 6 film are not replacement fenestration. They sit over or on the existing glass. Energy use still must not increase.

R503.1.1.1 replacement fenestration — Climate Zone 5 U-0.35 trap

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 for Climate Zone 5 and Marine 4 lists vertical fenestration U-0.30 and SHGC 0.40. A contractor who orders U-0.35 replacement windows for a Climate Zone 5 house has not met the table. One U-0.35 unit cannot hide behind averaging. Averaging is available only when more than one replacement unit is installed, and the area-weighted U-factor of all replacement fenestration units must still meet 0.30 (and SHGC 0.40 where the table requires it). Mixing a few U-0.28 units with U-0.35 units can work if the area-weighted U-factor is 0.30 or less. Installing only U-0.35 units cannot.

NFRC labels still matter. The rated U-factor and SHGC on the replacement product are what you compare to the table, not a center-of-glass marketing number.

R503.1.2 through R503.1.4 systems

R503.1.2 Heating and cooling systems. HVAC ducts newly installed as part of an alteration shall comply with R403. Exception: where ducts from an existing heating and cooling system are extended. Same idea as the addition exception in R502.3.2: stretching the existing trunk is not scored as a brand-new duct system. A new air handler and a new duct system installed during a gut remodel are newly installed and take R403.

R503.1.3 Service hot water systems. New service hot water systems that are part of the alteration shall comply with R403.5.

R503.1.4 Lighting. New lighting systems that are part of the alteration shall comply with R404.1. Exception: alterations that replace less than 10 percent of the luminaires in a space, provided that such alterations do not increase the installed interior lighting power. Replacing 2 of 24 kitchen cans is under 10 percent if lighting power does not go up. Replacing every luminaire in the space is not this exception, even if the new lamps are high-efficacy. Count luminaires in a space, not in the whole building, unless the alteration is defined that way on the drawings.

R504 repairs versus alterations

R504.1 sends repairs to R501.3 and this section. Work on nondamaged components necessary for the required repair of damaged components shall be considered part of the repair and shall not be subject to the requirements for alterations in this chapter. Replacing a cracked window's adjacent casing so the new glass will seat is still a repair if that casing work is necessary to complete the glass repair. Routine maintenance required by R501.3, ordinary repairs exempt from permit, and abatement of wear due to normal service conditions shall not be subject to the requirements for repairs in this section.

R504.2 lists what this code considers to be repairs:

1. Glass-only replacements in an existing sash and frame.
2. Roof repairs.
3. Repairs where only the bulb, ballast, or both within the existing luminaires in a space are replaced, provided the replacement does not increase the installed interior lighting power.

Inspector scenarios: U-0.35 windows and glass-only versus sash replacement

Replacement windows, U-0.35, Climate Zone 5. Twelve double-hung units are pulled and replaced with new sash-and-glazing products labeled U-0.35 / SHGC 0.32. Table R402.1.3 requires U-0.30 in Climate Zone 5. SHGC 0.32 meets the 0.40 Climate Zone 5 SHGC cap. The U-factor does not. Because every replacement unit is 0.35, an area-weighted average is still 0.35. Fail R503.1.1.1. Storm windows left in the truck do not convert this into exception 1; the sash was replaced.

Glass-only repair. A baseball breaks one lite. The sash and frame are sound. The glazing contractor installs a new insulated-glass unit in that existing sash and frame. R504.2 item 1 calls that a repair. Do not demand a U-0.30 NFRC label on a glass-only replacement as if R503.1.1.1 applied. If the same opening later gets a new sash and new glazing, it leaves the repair list and becomes replacement fenestration.

Roof repair versus reroof. Replacing a torn-off patch of shingles after a tree limb is a roof repair (R504.2 item 2). Stripping the whole roof to the sheathing on a house that had no cavity insulation, and leaving that sheathing exposed, is the R503.1.1 exception 5 alteration: insulate above or below the sheathing.

Plan-review and field sequence

1. Confirm the work is an alteration or a repair, not an addition and not a change in space conditioning (R501.2).
2. Apply R503.1 so unaltered portions stay put, the building is not less conforming, and energy use does not increase.
3. Walk R503.1.1 exceptions before writing an envelope correction. Empty opened cavities lose exception 2.
4. If sash and glazing are new, open Table R402.1.3. Climate Zone 5 vertical fenestration is U-0.30. Allow area-weighted averaging only across replacement units.
5. If only glass is replaced in the existing sash and frame, stay in R504.2.
6. Count luminaires in the space for the less than 10 percent lighting exception, and keep lighting power from increasing.

Change of occupancy, historic buildings, and maintenance are the next section.