Energy Code Air Sealing Inspection Checklist Under IRC 2018

Quick Answer

IRC 2018 Section N1102.4.1 provides a mandatory air barrier and insulation installation inspection checklist in Table N1102.4.1.1. This table lists specific locations that must be air sealed and insulated — including ceiling and attic top plates, walls, windows and doors, rim joists, plumbing and wiring penetrations, showers and tubs on exterior walls, electrical and HVAC penetrations, and common walls between units. The inspector works through each item on this list during the rough-in insulation inspection, or as supplementary verification even when a blower door test is also required by N1102.4.

What N1102.4.1 Actually Requires

Section N1102.4.1 of IRC 2018 requires that the building thermal envelope be durably sealed to minimize uncontrolled air movement between conditioned and unconditioned spaces. The code provides Table N1102.4.1.1, which lists specific building components and the required air sealing method for each. The inspector uses this table during the rough-in insulation inspection before drywall is installed over the air barrier components.

Key items from Table N1102.4.1.1 include: ceiling with attic above — the air barrier must be at the ceiling level, any dropped ceiling or soffit must be air-sealed at the top, and the insulation must be installed without gaps or voids. Wall assemblies — the air barrier must be on any exposed edge of insulation, and all gaps at penetrations through the wall thermal envelope must be sealed. Windows, skylights, and doors — the space between window and door jambs and surrounding framing must be sealed with an appropriate sealant or low-expansion foam. Rim joists — the cavity between floor joists at the perimeter must be both insulated and air-sealed, typically with closed-cell spray foam or rigid foam with sealed edges. Plumbing and wiring penetrations — every pipe, conduit, and wire penetrating through top plates, bottom plates, or the ceiling must be sealed at the penetration point.

Additional items include: showers and tubs located on exterior walls, which must have insulation between the fixture and the exterior wall and an air barrier at that location; recessed lights and electrical panels in the ceiling thermal envelope, which must be sealed and rated IC-AT (Insulation Contact and Air Tight) if installed in the ceiling; HVAC register boots in floors, ceilings, and walls, which must be sealed to the subfloor, ceiling surface, or wall surface at the boot-to-surface interface; attic access hatches and pull-down stair assemblies, which must be insulated and weather-stripped; and walls adjoining porches, garage spaces, and other unconditioned volumes, which require air barriers at their shared boundaries.

Why This Rule Exists

The air barrier checklist recognizes that a complete building air barrier is a system of many components, each of which must be properly installed to achieve the whole-building air tightness that N1102.4 requires. A single missed penetration — an unsealed plumbing stack through a top plate, an unfoamed recessed light fixture, or a dropped soffit open to the attic — can substantially increase whole-house air leakage even when all other locations are well-sealed. By enumerating the specific locations most prone to leakage failures, the code directs both contractors and inspectors to the high-risk areas that are most commonly missed in field construction. The checklist transforms air sealing from a vague requirement into a specific inspectable list of verifiable locations.

Air infiltration and exfiltration account for 25 to 40 percent of heating and cooling energy loss in typical residential buildings. The air barrier requirements in N1102.4.1 address the construction practices that most commonly produce high air leakage — they are directly responsive to failure modes documented in energy audits of new construction in U.S. climate zones.

What the Inspector Checks at Rough and Final

At the insulation rough-in inspection before drywall is installed, the building inspector physically works through Table N1102.4.1.1 and checks each listed location. For ceiling and attic areas, they verify that the top plate line is caulked or foamed, that attic bypasses at interior partition walls are sealed with a physical barrier, and that dropped soffits are air-sealed at their tops before insulation is installed over them. For rim joists at the foundation perimeter, they confirm the joist cavities are sealed and insulated. For plumbing and wiring penetrations through plates and the ceiling, they look for caulk, foam, or firestop putty at each penetration location.

The inspector also evaluates insulation installation quality for each location, checking that batts fill the cavity without gaps at electrical boxes, that insulation contacts the air barrier without voids or compressions, and that the overall installation reflects the quality required for the specified R-value. In jurisdictions where a blower door test under N1102.4 is also required, the visual air sealing inspection is in addition to the blower door test, not a substitute for it.

What Contractors Need to Know

Walk through the complete air sealing checklist before scheduling the insulation rough-in inspection. The most commonly missed items in field construction are: top plates at the intersection of interior walls and the ceiling, which are often not caulked; recessed light fixtures in the ceiling that are not IC-AT rated (standard recessed cans leak significant air into the attic even when surrounded by insulation); attic knee walls behind finished rooms that have no air barrier on the rafter side; the gap around plumbing supply and drain pipes through the bottom plate and subfloor; and HVAC register boots that sit on top of the subfloor without being sealed to the subfloor surface. Addressing all of these proactively before the inspection significantly reduces the chance of a failed inspection and the cost of corrective work after drywall installation.

For rim joists, two-component closed-cell spray foam is the most effective single-product solution — it both air-seals and insulates the rim joist in one application. Apply at least 2 inches of closed-cell foam to achieve approximately R-12 while simultaneously sealing the full perimeter of the joist cavity. Rigid foam cut to size can also be used, but all four edges of each rigid foam piece must be sealed with caulk or low-expansion foam — the rigid foam itself does not seal the edges, and unsealed edges make the installation air permeable.

Keep documentation of the air sealing products used at each location, particularly at firestop-required penetrations. The inspector may ask to verify that the correct firestop material was used at penetrations through fire-rated assemblies — standard expanding polyurethane foam is not an approved firestop material.

What Homeowners Get Wrong

Homeowners undertaking DIY insulation upgrades frequently focus on replacing batt insulation or adding blown-in insulation in the attic without addressing air sealing first. Adding insulation over unsealed air leakage paths captures the thermal benefit of insulation but does not address the air convection losses that often dominate energy use in leaky homes. In most existing homes, addressing the major air sealing locations before adding insulation depth provides more energy savings per dollar invested than the insulation upgrade alone. Seal the attic floor top plate penetrations, the attic hatch, recessed lights, and the rim joist before adding insulation depth.

Homeowners also commonly use inappropriate products. Standard polyurethane expanding foam such as commercially available spray cans is not appropriate for firestop penetrations through fire-rated assemblies — listed intumescent firestop materials must be used in those applications. However, low-expansion foam is appropriate for sealing most non-rated penetrations such as plumbing and wiring through standard interior wall and floor plates.

A third common mistake is adding blown-in attic insulation up to or over the eave area without air-sealing the top plate first. Blowing insulation over unsealed top plates buries the air leakage path under insulation but does not seal it — the top plate-to-ceiling gap remains an active air bypass into the attic. Fixing it after insulation is installed requires moving insulation to access the top plate area, which is significantly more time-consuming than sealing before insulation installation.

State and Local Amendments

IRC 2018 states including TX, GA, VA, NC, SC, TN, AL, MS, KY, and MO adopted the N1102.4.1 air sealing checklist requirements through the 2018 IECC. The checklist in Table N1102.4.1.1 applies identically in all climate zones — air sealing requirements are not adjusted by climate zone the way R-value requirements are. All new construction in all climates must address the same list of required air barrier locations. Local jurisdictions may require the inspector to physically verify each item on the checklist rather than accepting a contractor-signed affidavit as adequate documentation.

IRC 2021 retained the air sealing checklist in N1102.4.1 with the same Table N1102.4.1.1 items. Clarifications were added for specific configurations such as shallow attics and spray foam wall assemblies, but no checklist item was removed and no major change to the list of required air sealing locations was made from IRC 2018 to IRC 2021.

When to Hire a Licensed Contractor

Air sealing as part of new construction is typically performed by the framing contractor and insulation contractor as part of their scope of work. For existing home energy retrofits, a BPI-certified building performance contractor should perform a diagnostic blower door test first to identify the major leakage locations using instrumentation, then seal those locations and retest to verify improvement. DIY air sealing in existing homes is practical for accessible locations such as attic top plates, rim joists, and around windows and doors, but a professional energy audit identifies the highest-value leakage locations that may not be obvious to an untrained observer working without diagnostic equipment.

Common Violations Found at Inspection

• Top plates at interior wall-to-ceiling intersections not caulked or foamed — the most common attic air bypass location in new construction.
• Recessed lights in the ceiling not IC-AT rated (Insulation Contact and Air Tight) — standard recessed cans leak significant air into the attic.
• Rim joist not insulated or sealed — a major thermal bridge and air leakage path at the floor perimeter in every floor level above unconditioned space.
• Plumbing stack and drain pipe penetrations through top and bottom plates not sealed with appropriate sealant or firestop material.
• Shower or tub on an exterior wall with no air barrier between the fixture rough-in and the insulation, allowing unconditioned air to contact the fixture.
• HVAC register boot not sealed to the subfloor or ceiling surface — allows direct air exchange between the crawlspace or attic and the duct supply airstream.
• Attic hatch not insulated or weather-stripped, creating a high-leakage bypass point in the ceiling air barrier every time the hatch is opened and closed.