Quick answer
Air sealing is the work of closing the cracks, holes and gaps in a home’s outer shell so that heated or cooled air cannot leak out and outdoor or attic air cannot leak in, using caulk, foam, gaskets, weatherstripping and rigid blocking.
It targets the air barrier, not the insulation. A remodel is the best time to do it, because walls, ceilings and floors are open and the leaks that hide behind finishes can be reached.
Quick facts
The key facts about Air Sealing, with sources:
Key takeaways
- Air sealing blocks drafts; insulation slows heat flow. A house needs both, and sealing usually comes first.
- The biggest leaks are often hidden: attic bypasses, rim joists, recessed lights and holes for pipes and wires.
- A blower door test measures how leaky a house is in air changes per hour at 50 pascals.
- The 2021 IECC caps new-home leakage at 3.0 ACH50 in most U.S. climate zones and 5.0 in the warmest.
- Tighter homes need planned ventilation and safe venting for gas appliances.
Air sealing in plain English
A house leaks air through hundreds of small openings. Some are obvious, like a gap under a door. Most are hidden: the hole where a plumbing vent passes into the attic, the seam where the wall meets the foundation, the space around a ceiling light. Together they act like an open window you never see.
The U.S. Department of Energy puts the difference this way: insulation is like a sweater, and air sealing is like a windbreaker 2.
A sweater keeps you warm in still air, but wind goes right through it. Fiberglass and loose-fill insulation work the same way. If air moves through them, they lose much of their value.
Air sealing builds or repairs the air barrier, the continuous layer that stops air movement. In a typical house that layer is a mix of drywall, sheathing, framing, sealed joints and gaskets.
The job is to find the breaks in it and close them. For how the air barrier fits with the other layers, see our building envelope page.
How air leaks happen and how sealing stops them
Air moves when there is a pressure difference. In winter, warm air rises and pushes out through the top of the house, while cold air is pulled in low. Wind and exhaust fans add more pressure.
DOE notes that leaks often show up where rising warm air is replaced by cooler air, such as between an attic and the rooms below, and where dirty spots on insulation show air passing through 2.
Sealing works by closing the path. Small gaps get caulk. Larger gaps get spray foam. Big openings, like a chase or a dropped soffit, get rigid blocking sealed at the edges. Moving parts, like doors and windows, get weatherstripping 2.
The code also asks that sealing allow for movement. The 2021 International Energy Conservation Code (IECC) says sealing methods between different materials must allow for differential expansion and contraction 1. A rigid caulk across a joint that moves will crack and leak again.
- Attic floorPlumbing vents, wiring holes, chases, attic hatch
- Ceiling fixturesRecessed lights and fan housings
- Rim joistWhere floor framing sits on the foundation
- Windows and doorsGaps behind trim; worn weatherstripping
- Wall penetrationsPipes, vents, wires, outlets on outside walls
- Ducts and fansDuct joints and fan boxes in unconditioned space
Locations drawn from DOE’s air-sealing consumer guide and the 2021 IECC air barrier table. Source: [2] [1]
Types of air-sealing materials and where each fits
| Material | Best for | Notes |
|---|---|---|
| Acrylic latex caulk | Small, stable gaps: trim, drywall edges, sill joints | Listed by DOE for DIY sealing 2 |
| High-temperature silicone caulk | Around flues, vents and pipes from chimneys, furnaces, water heaters | DOE recommends a professional for this work 2 |
| Expanding polyurethane foam | Larger gaps around pipes, wires and rough openings | Some foams also insulate 2 |
| Water-based foam | Gaps where less expansion is wanted | Listed by DOE 2 |
| Weatherstripping | Moving parts: doors, sashes, attic hatches | Many types: tension seal, felt, foam, door sweeps, bulb seals 2 |
| Gaskets | Recessed lights, outlet boxes on outside walls | IECC requires sealed recessed lights and air-sealed boxes in the envelope 1 |
| Rigid blocking (board) sealed at edges | Large openings: chases, soffits, kneewalls | Required by the IECC air barrier table at some locations 1 |
Example: what a blower door number means
A blower door test pulls the house to 50 pascals of pressure and measures airflow. Results are reported as air changes per hour at that pressure (ACH50) 1. Here is how the 2021 IECC sorts those results for new homes and additions that use the prescriptive path 1.
| Result | Climate zones 0–2 | Climate zones 3–8 |
|---|---|---|
| 2.5 ACH50 | Meets the 5.0 limit | Meets the 3.0 limit |
| 4.0 ACH50 | Meets the 5.0 limit | Fails the 3.0 limit |
| 6.0 ACH50 | Fails; also above the 5.0 cap for any path | Fails; also above the 5.0 cap for any path |
The 2021 IECC sets 5.0 ACH50 as the maximum for any compliance path, and 3.0 for the prescriptive path in climate zones 3 through 8 1.
Testing must follow ANSI/RESNET/ICC 380, ASTM E779 or ASTM E1827, and the signed report goes to the code official 1. Existing homes being remodeled are not always tested; ask your building department. For the test itself, see our blower door test page.
Where air sealing shows up in a remodel
In the bid. Look for a line that names air sealing separately from insulation, and lists the locations: top plates, penetrations, rim joist, recessed lights. “Insulation per code” alone often means no sealing.
In the inspection. The IECC lets the code official require an approved third party to inspect air barrier and insulation work 1. Some jurisdictions add an insulation or air-barrier inspection before drywall.
In an energy assessment report. A home energy assessor uses a blower door and an infrared camera to find leaks and gives you a prioritized list 2. See our home energy audit entry.
In your schedule. Sealing has to happen after rough-ins and before insulation and drywall. Our remodel timeline tool shows where that window falls.
Seal first, then insulate
Once loose-fill insulation is blown over an attic floor, the leaks under it are buried. DOE notes that hard-to-find attic leaks covered by insulation are the ones a do-it-yourself approach misses 2. Seal while you can still see the holes.
Benefits and limits of air sealing
Benefits
What air sealing cannot do
Air sealing does not add R-value. A sealed, uninsulated attic is still cold. It also does not fix leaky ducts in the attic on its own; ducts are their own sealing job.
And it cannot replace a vapor retarder where one is needed, since vapor moves by diffusion as well as with air. See our vapor retarder page for that layer.
Savings claims vary by source, and none is a promise.
ENERGY STAR’s consumer page says sealing and insulating can save up to 10% on annual energy bills 3, while its methodology page reports an average 15% on heating and cooling costs, or 11% of total energy costs, from modeling typical homes built 1970 to 1989 4. Your house may differ.
What drives the cost of air sealing
We do not quote prices. The cost drivers are access, scope and testing. Open walls and ceilings during a remodel make sealing far easier than working through finished surfaces.
Attics with deep existing insulation take longer, because the insulation must be moved to reach the leaks. The number of penetrations, recessed lights, chases and kneewalls sets the hours.
Adding a blower door test before and after adds a measured result.
Life span depends on the material and on movement. Weatherstripping on doors wears out with use. Caulk across moving joints cracks. Foam and sealed blocking at hidden locations last as long as nothing disturbs them.
For budgeting a whole project, see our remodeling cost guide. Federal tax credits for home improvements have changed; the 25C credit expired on 31 December 2025.
How air sealing fits into a remodel
- Have a home energy assessment or blower door test to find the big leaks, if the budget allows 2.
- Plan ventilation and check gas appliances before tightening the house 2.
- After rough-ins pass, seal penetrations through top plates, floors and outside walls.
- Seal and gasket recessed lights and outlet boxes in the envelope, or use air-tight rated parts 1.
- Block and seal large openings: chases, soffits, kneewalls, rim joists 1.
- Insulate after sealing, then test again if a number is required 1.
Keeping the seal intact
- Replace worn door weatherstripping and sweeps when you see light or feel drafts.
- Re-seal around new holes: every new cable, pipe or vent through the shell opens a leak.
- Check the attic hatch gasket and latch.
- Ask trades to seal what they cut, and check it before drywall.
Risks, warning signs and when to call a pro
- Gas appliances that are not sealed-combustion. They need enough air; poor venting can release carbon monoxide 2.
- Condensation on windows or musty smells after sealing. Signs the house may need more ventilation 2.
- Foam or caulk against flues and chimneys. These need heat-rated materials and clearances 2.
- Older recessed lights in the attic floor. Non-IC fixtures must stay clear of insulation; check before sealing over them.
Check combustion safety before tightening
DOE warns that if combustion appliances such as furnaces, water heaters, stoves and fireplaces do not get enough air, they can release carbon monoxide into the home. Have a certified assessor or HVAC contractor test venting and plan ventilation as part of any air-sealing job, and install CO alarms 2.
Codes and standards for air sealing
2021 IECC Section R402.4. R402.4.1 requires the thermal envelope to be sealed, with methods that allow for movement between materials.
R402.4.1.1 requires installation to follow Table R402.4.1.1 and the maker’s instructions, and lets the code official require third-party inspection.
R402.4.1.2 requires testing at 50 pascals by ANSI/RESNET/ICC 380, ASTM E779 or ASTM E1827, with a 5.0 ACH50 maximum.
R402.4.1.3 sets 5.0 in zones 0–2 and 3.0 in zones 3–8 for the prescriptive path. R402.4.5 requires sealed, IC-rated recessed lights, and R402.4.6 air-sealed outlet boxes 1.
Remodels. The IECC treats alterations to existing homes differently from new homes, and the model code does not force a whole-house test for every remodel. Additions are often held to new-home rules. Ask your jurisdiction which edition it uses and what applies.
Where to check adoption. The U.S. DOE Building Energy Codes Program tracks which energy code each state uses 5.
Air sealing vs related layers and tests
| Term | What it controls | Main difference |
|---|---|---|
| Air sealing | Air movement through gaps | Closes holes in the air barrier 2 |
| Insulation (for example blown-in insulation) | Heat flow by conduction | Slows heat; does not stop air 2 |
| Vapor retarder | Moisture diffusion | Slows water vapor, not drafts |
| Whole-house ventilation | Planned fresh air | Adds controlled air after sealing 2 |
| Blower door test | Measures leakage | Tells you how well sealing worked 1 |
Air-sealing myths
- Myth A house needs to breathe, so sealing is bad.
- Reality Uncontrolled leaks are not good ventilation; DOE says to pair sealing with planned ventilation 2.
- Myth More insulation fixes drafts.
- Reality Insulation does not block air movement; sealing does 2.
- Myth Sealing windows and doors is enough.
- Reality Those leaks are the most obvious, but many are hidden in attics, rim joists and walls 2.
- Myth Any caulk works anywhere.
- Reality Flues and chimneys need high-temperature materials; moving joints need flexible sealants 2 1.
- Myth Every remodel requires a blower door test.
- Reality Testing is set for new homes in the model code; remodel rules vary by jurisdiction 1.
Climate zone changes the target
The 2021 IECC sets a looser prescriptive limit, 5.0 ACH50, in the hottest climate zones 0 through 2, and a tighter 3.0 ACH50 in zones 3 through 8, which covers most of the country 1.
In cold zones the payoff is mostly in winter heating; in hot, humid zones sealing also keeps damp outdoor air out of walls and attics. Your state may use an older or amended energy code; the DOE Building Energy Codes Program lists adoption by state 5.
When air sealing should be on your remodel list
If walls, ceilings or the attic floor will be open, add air sealing to the scope. It is cheapest then. It matters most on top-floor ceilings below an attic, on additions, in basements with exposed rim joists, and anywhere you add recessed lights.
Pair it with a ventilation plan and a combustion safety check. Then decide on insulation. Planning a whole-house project? Our whole-home renovation page covers how energy work fits the sequence.
- If Attic insulation is being added or replaced
- Then Seal the attic floor first
- If Walls or ceilings are open
- Then Seal penetrations and top plates before drywall
- If House has older gas appliances
- Then Get a combustion safety test before tightening
- If You want proof of results
- Then Blower door test before and after
Questions about Air Sealing
What is air sealing a house?
Air sealing is closing gaps in the outer shell of a home so conditioned air does not leak out and outside or attic air does not leak in. Installers use caulk, spray foam, weatherstripping, gaskets and sealed blocking. It works together with insulation, which slows heat but does not stop air.
Should I air seal before insulating?
Yes. Once insulation covers an attic floor or fills a wall, the leaks under it are hard to reach; DOE notes that leaks covered by attic insulation are the hardest to find. During a remodel, seal after rough-in inspections and before insulation and drywall.
Where are the biggest air leaks in a house?
Often in places you cannot see: holes for plumbing vents and wires into the attic, chases and soffits, recessed lights, the rim joist above the foundation, and the attic hatch. Doors and windows leak too, but they are usually not the largest source. A blower door test with an infrared camera finds them.
How much can air sealing save?
ENERGY STAR says sealing and insulating can save up to 10% on annual energy bills. Its methodology page reports an average 15% saving on heating and cooling, or 11% of total energy costs, from modeling typical homes built from 1970 to 1989. Your result depends on your house and climate.
Can a house be too airtight?
A house can be too tight without planned ventilation. DOE says to decide how much fresh air is needed and to make sure combustion appliances get enough air. The fix is controlled ventilation, such as exhaust fans or a whole-house system, not leaving random leaks.
What is ACH50?
ACH50 is air changes per hour at 50 pascals of pressure, the result of a blower door test.
It tells you how many times the house’s air volume would be replaced each hour at that test pressure.
The 2021 IECC caps new homes at 5.0 ACH50, and 3.0 in most climate zones on the prescriptive path.
Is air sealing required by code?
For new homes, yes. The 2021 IECC requires a sealed thermal envelope, installation per its air barrier table, and a blower door test. Remodels and additions follow your jurisdiction’s rules for existing buildings, which vary. Ask the building department what applies to your project.
What materials are used for air sealing?
DOE lists caulk, including acrylic latex and high-temperature silicone; spray foam, including expanding polyurethane and water-based foams; and many kinds of weatherstripping. Large openings get rigid board sealed at the edges, and recessed lights and outlet boxes get gaskets or air-tight rated parts.
Can I air seal myself?
You can handle obvious leaks like door weatherstripping and caulking trim and wall penetrations, as DOE describes. Leaks near flues and chimneys, combustion safety checks and attic work over deep insulation are better left to a certified energy professional or contractor.
Sources
- ICC, 2021 International Energy Conservation Code, Chapter 4 [RE] Residential Energy Efficiency (R402.4), retrieved .
- U.S. Department of Energy, Energy Saver: Consumer Guide to Air Sealing the Home (DOE/EE-2470), retrieved .
- ENERGY STAR, Seal and Insulate with ENERGY STAR, retrieved .
- ENERGY STAR, Methodology for Estimated Energy Savings (Seal and Insulate), retrieved .
- U.S. DOE Building Energy Codes Program, retrieved .
Expert review
Written by the HyreRemodel Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Code limits, test methods, installation and recessed-light and outlet-box rules were read from 2021 IECC R402.4 on ICC Digital Codes.
Leak locations, materials, combustion safety and the sweater/windbreaker comparison are from DOE’s Consumer Guide to Air Sealing the Home. Savings figures are quoted from ENERGY STAR’s consumer and methodology pages as stated, with their basis.
The example table applies the IECC limits to sample results. No prices are given.
Suggest a correction. We fix errors and say what changed.