Home air sealing for the drafts a furnace can't fix
Home air sealing closes the specific gaps that let warm air leave a Massachusetts or Rhode Island house, from the attic top plate down to the rim joist at the foundation. A furnace can only heat air that stays inside the house long enough to matter, and every open seam undoes part of what it just did.
What home air sealing is, and why the stack effect makes it matter
Air sealing is the work of closing the specific gaps, cracks, and penetrations that let indoor air escape a house and let outdoor air replace it, using foam, caulk, gaskets, and rigid material matched to what each gap is made of and what sits behind it. It is a different trade from insulation. Insulation slows how fast heat moves through a material that is already in place. Air sealing stops air itself from moving through an opening, which is a bigger and faster path for heat loss than most homeowners expect, and it is one part of the same shell work covered on the insulation services page.
The reason it matters more than the size of the gaps would suggest is the stack effect. Warm air is lighter than cold air, so inside a heated house it rises and pushes out through every opening near the roofline, the top plates, the attic hatch, a chimney chase, while the pressure drop that creates pulls cold outside air in low, through the rim joist and basement windows. The taller the house and the colder the outdoor temperature, the harder that chimney-like draft pulls, which is exactly why it shows up hardest in a New England winter and exactly why the leaks at the top of a house and the leaks at the bottom of a house are really the same problem working together.
The signs a house is losing air it paid to heat
Most of these show up as an annoyance long before anyone connects them to an open seam in the attic or at the sill.
Drafts at outlets and baseboards
A cold draft at an outlet, a switch plate, or along a baseboard on an exterior wall is air moving through the wall cavity behind it. Wall insulation closes that same cavity from the inside.
A room that never balances
One room that never quite matches the thermostat, often a corner bedroom or a room over a garage, usually has more open framing feeding it than the rooms around it.
Dust lines at the carpet edge
A dark line of dust along the edge of a carpet or under a baseboard is airborne dust settling out of the same draft that is pulling conditioned air out of the room.
A high bill with new insulation already in
A heating bill that stays high after fresh insulation goes in usually means the air moving through the shell was never addressed, so the insulation is working against airflow it cannot stop on its own.
Ice dams along the eaves
A ridge of ice at the roof edge in winter is heat escaping unevenly into the attic and melting snow from below. Ice dam prevention traces that heat back to the same top-plate and chimney-chase leaks that air sealing closes.
Where the leaks actually are, in the order a crew seals them
A crew works a house in a set order, from the attic down to the foundation, because the biggest leaks sit at the top and the order keeps the same access open from one point to the next instead of backtracking through the house.
Attic top plates
Where the top of an exterior wall meets the attic floor, this seam sits at the strongest point of the stack effect and is closed first. Attic insulation goes in only after it is sealed.
Chimney and flue chases
The framed shaft boxing in a masonry chimney or metal flue is often open straight down to the basement, and it is sealed with materials rated for the heat next to it.
Plumbing and wire penetrations
Every pipe and cable that runs from a heated floor into the attic leaves a ring of open framing around it, closed one penetration at a time.
Recessed lights
Older can lights cut into a ceiling with no air-tight housing behind them are a direct opening straight into the attic.
Attic hatch
The pull-down stair or hatch panel is usually the single largest unsealed opening in the house, and it gets a gasket and weatherstripping, not just a cover.
Rim joist
The band of framing where the floor system sits on the foundation wall is sealed from inside the basement or crawl space, alongside any basement insulation already planned for the same area.
Basement windows
Older sash and frames rarely seal cleanly against the masonry opening around them, and the gap is closed with the same materials used at the rim joist.
Duct boots
Where a supply or return duct meets the floor, wall, or ceiling, the metal-to-drywall seam is almost never sealed at installation and gets caulked or foamed in place.
On the day of the work, the crew starts with a blower door test, part of a free home energy assessment, to measure how much air the house is actually losing, works down this list from the attic to the basement, and finishes with a second blower door reading to confirm how much of that leakage closed. A typical single-family home is done in a day. A house with extensive balloon framing, several chimney chases, or knob-and-tube wiring that has to be routed around first can run into a second day.
Point the leak-point map at your own house
Every leak point above gets a different material, chosen by what sits on the other side of the gap, not by habit. One-part canned foam fills small, irregular gaps around a single penetration. Two-part spray foam expands to fill a larger cavity in one pass, such as an open stud bay at a rim joist. Fire-rated caulk and rigid foil-faced board go anywhere near a heat source, because a chimney or flue chase carries live combustion byproducts and code requires clearance from anything combustible there, which rules out plastic spray foam entirely at that one location. Gaskets go behind outlet and switch plates and around the attic hatch frame. Weatherstripping goes anywhere a panel has to open and close, like the attic hatch itself.
Leak-point map, select a point
Attic top plate
Sealed with two-part spray foam or fire-rated caulk where the wall framing meets the attic floor, the first stop on every job because it sits at the strongest point of the stack effect.
Air sealing is always finished before any insulation goes in behind it. Insulation buried over an air leak just gets bypassed by moving air and can trap the moisture that air carries, so the sequence is never reversed on a Complete Home Comfort job.
What decides what a home air sealing job costs
There is no single number for air sealing, because two houses with the same square footage can have very different amounts of open framing behind the walls and under the floor. These are the factors that move the number, without a number attached to any of them.
An older balloon-framed house has more open stud bays running floor to floor than a newer platform-framed one, and each open bay is its own leak path.
A full-height, walk-in attic gets sealed faster than a cramped knee-wall attic or one reached only through a small scuttle opening.
A house with more plumbing stacks, wire runs, and duct penetrations through the attic floor has more individual points to close.
A house with one masonry chimney takes less time to seal at the chase than one with a chimney plus a separate metal flue for a second heating appliance.
Where knob-and-tube wiring runs through a bay that needs to be sealed and later insulated, an electrician has to clear or reroute it first, which adds a step before that bay can be finished.
Unsealed ductwork running through an unconditioned attic or basement adds its own set of duct boot seams to the scope, on top of the building's own penetrations.
What New England winters and older housing add to the job
A lot of the towns we work in are full of houses built well before air sealing was part of the plan, and both the age of the housing stock and the climate change the job. Pre-1980 construction is common across Norfolk County and the towns around it, and a lot of it is balloon-framed, with stud bays that run uninterrupted from the basement sill to the attic instead of stopping at each floor. Those open bays are some of the largest, least obvious leak paths in an older house, and they get found and sealed as part of the same visit that addresses the attic and the rim joist.
Cold winters make the stack effect stronger than it would be in a milder climate. The applicable assessment path, Mass Save in Massachusetts or Rhode Island Energy through RISE in Rhode Island, measures air leakage so the scope is based on the house rather than a guess and the finished result can be checked.
The scope for a home air sealing job is approved before work is scheduled, whether the address follows Mass Save in Massachusetts or Rhode Island Energy through RISE. Complete Home Comfort serves 47 Massachusetts municipalities and all 26 Rhode Island municipalities with the same scope-first process.
Frequently asked questions
Air sealing closes the openings that let indoor air escape and outdoor air in. Insulation slows how fast heat moves through whatever material is already in place. A house can have thick insulation and still lose a lot of heat if air is moving freely underneath or around it, which is why home air sealing is done first and insulation goes in after.
The scope is targeted at specific leak points, attic penetrations, chases, the rim joist, rather than sealing every possible gap in the house at once. A blower door test measures the result, so the work is sized to the house rather than guessed at, and the assessment that comes before it is what defines how far the scope goes.
Yes. Ice dams form when heat escaping into the attic melts snow unevenly on the roof above it, and most of that heat rides warm air out through the same top-plate, chimney-chase, and recessed-light leaks that air sealing closes. Closing those points is usually the biggest single change a homeowner can make to stop dams from forming in the first place.
Yes, and it is common work in the older colonials and capes around Franklin and the rest of Norfolk County. Balloon framing leaves stud bays that run uninterrupted from the basement to the attic, so the top plate and rim joist points on that kind of house usually carry more of the leakage than they would on a newer, platform-framed home.
Mass Save in Massachusetts and Rhode Island Energy through RISE both evaluate air sealing and insulation as part of the program scope for the address. Air sealing is written first because it has to happen before insulation, and the paperwork and sequence are handled together.
Find out where your house is actually losing air
The assessment is free, it starts with a blower door test, and it ends with a written scope and a number before anyone touches a wall or an attic floor.