Short answer: sealing the air leaks between your rooms and the attic is one of the least expensive upgrades that makes a real dent in heating and cooling use. The materials are ordinary (caulk, spray foam, sheet metal and weatherstripping), the biggest leaks sit in one place, and ENERGY STAR says sealing air leaks and adding insulation can save up to 10% on your annual energy bills. Two catches: the leaks that matter are hidden under the attic insulation, not around your windows, and homes with gas appliances need a safety check once the house is tighter.
Why the attic, and why sealing comes first
ENERGY STAR calls the attic the place where you usually find some of the largest opportunities to save energy, and its rule is simple: always do attic air sealing before adding insulation. Insulation slows heat moving through the ceiling, but air pushes right through fiberglass. If the gaps underneath stay open, part of what you pay to heat or cool keeps escaping.
The windows and doors you can feel drafts around are not the main problem. ENERGY STAR says leaks through doors, windows and walls usually have the least impact on energy use, while the most significant leaks in most homes are hidden in the attic.
A Tri-Valley PG&E bill pays for both seasons, and the same holes cost you in both:
- Winter. ENERGY STAR compares a house to a chimney: warm air rises into the attic and pulls cold outside air in around windows, doors and lower openings. The furnace keeps reheating that new air.
- Summer. The same openings connect your rooms to an attic full of what ENERGY STAR calls super-heated air. ENERGY STAR also warns that an attic fan in an attic that isn’t sealed from the house will pull cooled air up out of your rooms, making the air conditioner work harder.
Where the leaks hide
ENERGY STAR’s advice is to plug the big holes first and not worry about every tiny one. The usual suspects:
- the tops of interior and exterior walls, where they meet the attic floor
- dropped soffits, the dropped-ceiling areas that are often open to the attic above
- recessed lights
- holes for wiring, plumbing pipes and vent stacks
- the gap around the furnace or water heater flue, and the chase that hides ducts
- the attic hatch or pull-down stairs
- the spaces behind and under kneewalls, in homes with a bonus room built into the attic
The leaks are usually buried under insulation, but they leave a clue. ENERGY STAR notes that insulation that looks darkened or dirty in spots has been filtering dusty air from the house. That’s where air is moving.
What seals what
The materials are basic. The skill is in matching each one to the gap:
- Small gaps (up to about 1/4 inch): silicone or acrylic latex caulk, including around electrical boxes.
- Larger gaps (about 1/4 inch to 3 inches): expanding spray foam, the usual fix for wiring and plumbing holes.
- Big openings like open soffits and chases: a cover of rigid foam board, drywall or reflective foil, sealed around the edges with caulk or adhesive.
- Furnace flues and chimneys: aluminum flashing and high-temperature caulk, never spray foam. ENERGY STAR notes that building codes usually require 1 inch of clearance from metal flues (2 inches from masonry chimneys) to anything combustible, including insulation, so a metal dam goes around the flue before insulation goes back.
- The attic hatch: self-sticking weatherstrip around the edges and a piece of rigid foam or fiberglass on the back. ENERGY STAR’s advice is to treat the attic door like a door to the outside.
Safety checks that come with a tighter house
Air sealing changes how a house breathes, so a few checks belong in the plan:
- Gas appliances. ENERGY STAR warns that sealing can, in some cases, cause naturally venting appliances like water heaters to backdraft exhaust into the home. It recommends inspection and testing by a home energy professional, and says combustion problems should be fixed before air sealing begins.
- Indoor air. A tighter house can trap pollutants such as carbon monoxide, radon and volatile organic compounds, and may need added mechanical ventilation. After reducing air leaks, the EPA recommends testing your home for radon with a test kit.
- Old wiring. Knob-and-tube wiring (pre-1930) can be a fire hazard in contact with insulation. ENERGY STAR says to have a professional correct it before going further.
- Vermiculite. If the attic has pebble-like vermiculite fill, leave it alone and read our guide on removing old insulation or adding on top first.
Doing it yourself vs hiring it out
ENERGY STAR publishes a step-by-step attic air sealing project for homeowners, and the hatch and a few obvious holes make a reasonable weekend project. Walk only on the joists or truss chords, wear a mask, eye protection and gloves, and remember that furnace flues can be very hot.
The harder part is the whole attic. Many leaks sit under the insulation, some of them out near the eaves where the roof is low. That’s why air sealing often happens together with an insulation job: when the old insulation comes out, or before new insulation goes in, every top plate and wiring hole is in plain sight. Our guide to blown-in vs batt insulation covers the next step, and if your bedrooms run hot and cold, see why your upstairs is cold in winter and hot in summer.
If your household income is limited, PG&E’s Energy Savings Assistance program provides weatherstripping, caulking, attic insulation and other upgrades at no cost to customers who qualify. As of October 2026 the income limit for a household of four is $82,500 (June 2026 to May 2027 guidelines). Call PG&E at 1-800-933-9555 to apply.
What we look for
Whether your home is in Walnut Creek, Alamo, Danville or Windemere in San Ramon, the free in-home estimate starts in the attic. We look for dirty spots in the insulation, open soffits and chases, gaps around the flue and recessed lights, the hatch seal and the ducts. You get photos of what we find and a written quote, so you can see where the leaks are before deciding anything.
Want to find the leaks in your attic? Call (510) 725-4073 or request a free estimate. More about our attic insulation and air sealing, including attic work in Walnut Creek.
Sources: ENERGY STAR, seal and insulate · ENERGY STAR, attic air sealing project · ENERGY STAR, assess the level of opportunity · ENERGY STAR, locating air leaks · ENERGY STAR, sealing the attic hatch · ENERGY STAR, attic ventilation and attic fans · ENERGY STAR, combustion safety and indoor air · CPUC, Energy Savings Assistance program