How to caulk and weatherstrip a house

Air leaks are the cheapest energy problem to fix in a house, and the fix is a tube of caulk and an afternoon.

Published September 11, 20266 min readEasy · 2-4 hrs

On this page

Where houses leak
Finding the leaks
What you need
Steps: caulking
Steps: weatherstripping
When to stop and call a pro
What to record
Common questions
What to do next

Seal the gaps a house leaks through in two ways: caulk for joints that do not move (around window and door frames, where pipes and wires come through walls, along trim), and weatherstripping for parts that do (the edges of doors and operable windows). That is the Department of Energy's division of labor, and the whole house can be done in an afternoon with a caulk gun, a few tubes, and a roll of foam or rubber strip.

Air leaks cost more than comfort. Warm air leaving through the attic pulls cold air in at the bottom of the house; humid air moving through a wall condenses inside it; water follows open exterior joints behind the siding. Sealing the obvious gaps is the first weatherization step the DOE recommends, before insulation.

Where houses leak

Documented

The Department of Energy's Consumer Guide to Air Sealing says caulk is generally used for cracks and openings between stationary components such as door and window frames, and weatherstripping for components that move, such as doors and operable windows. It lists the places to seal: where plumbing, ducting, or wiring comes through walls, floors, ceilings, and soffits; behind outlet and switch plates (foam gaskets); larger gaps with foam sealant; and, only with fire-resistant materials, around chimneys, furnaces, and gas water heater vents.

Where	Inside or out	Product
Window and door frames where they meet siding or trim	Outside	Exterior paintable caulk
Window and door casings where they meet the wall	Inside	Interior acrylic latex caulk
Pipes, cables, dryer vent, hose bibs, AC lines through the exterior wall	Outside	Exterior caulk; low-expansion foam for large gaps
Rim joist and sill plate in the basement or crawlspace	Inside	Caulk or foam
Outlets and switches on exterior walls	Inside	Foam gaskets behind the plates
Attic hatch, recessed lights, top plates	Attic	Weatherstrip the hatch; foam and caulk penetrations
Door edges and bottoms	Doors	Weatherstripping, door sweep, threshold gasket
Operable window sashes	Windows	Weatherstripping (V-strip, foam, or bulb)
Flues, chimneys, water heater vents	Anywhere	High-temperature only; the DOE says use a pro

Finding the leaks

The DOE's Energy Saver guide describes the smoke test: on a windy day, hold a lit incense stick near windows, doors, outlets, plumbing and light fixtures, and the attic hatch; where the smoke stream travels sideways, air is moving. Also look for dirty streaks on insulation or at the edges of carpet along exterior walls (dust filtered out of moving air), and feel with the back of your hand around outlets and window edges on a cold day.

For leaks you cannot find, the DOE recommends a professional energy assessment with a blower door test. That is the right call for a house that feels drafty after the obvious joints are sealed.

What you need

A caulk gun and a few tubes: exterior paintable caulk, interior acrylic latex caulk
A can of low-expansion window and door foam for gaps wider than a quarter inch
Weatherstripping in the type your doors and windows take (look at what is there), plus a door sweep if the bottom of an exterior door shows light
Foam outlet gaskets
A caulk removal tool or a putty knife, a utility knife, rubbing alcohol, and rags
A damp cloth or a caulk-smoothing tool for tooling the bead
A ladder for the upper windows, with someone footing it

Steps: caulking

Remove the old caulk where it has cracked or pulled away. Cut it out with the removal tool, scrape the joint clean, and wipe with alcohol. New caulk on top of failed caulk fails with it. Done when: the joint is bare and dry.
Cut the tube tip at an angle, small, so the bead is a little wider than the gap. Puncture the inner seal.
Run a steady bead along the joint, pushing the gun ahead of the bead rather than dragging it, so the caulk is forced into the gap.
Tool the bead within a few minutes: a wet finger or the smoothing tool, one pass, pressing the caulk into both sides of the joint. Done when: the bead is concave, touches both surfaces, and has no gaps.
For gaps wider than the bead can bridge, use the foam, sparingly; it expands. Trim flush once cured and caulk over it outdoors, where sun degrades bare foam.
Let exterior caulk cure per the label before rain or paint.

Steps: weatherstripping

Check each exterior door with the paper test at the top, sides, and bottom. Note where it fails.
Pull off the failed strip. Clean the channel or the stop with alcohol.
Install the new strip of the same type: kerf-in strips press into the slot in the door stop; adhesive foam or rubber sticks to the stop face; V-strip tacks or sticks to the jamb. Cut to length with the utility knife. Done when: the door closes with light, even resistance all the way around and the paper test holds.
Fit a door sweep or a threshold gasket if daylight shows under the door. Adjust so it touches the threshold without dragging.
Weatherstrip the attic hatch or pull-down stair the same way; it is the biggest single leak in many houses.
Add foam gaskets behind the outlet and switch plates on exterior walls. Breaker off for the circuit, plate off, gasket on, plate back on.

When to stop and call a pro

Leave the flue, chimney, furnace vent, and water heater vent sealing to a professional; the wrong material near a hot flue is a fire risk, and the DOE says so. Call a window company if a window's sash is loose in the frame or the glazing seal has failed (fogging between panes); no weatherstrip fixes that. Call an energy assessor if the house is still drafty or the bills are still high after the obvious sealing; a blower door finds what a candle cannot. Do not seal a house so tight that combustion appliances cannot draw air without also arranging for ventilation; that is the assessor's job to check.

On a new build, cracked exterior caulk at windows and doors in the first year is worth reporting to the builder in writing before you recaulk it; take the photos first.

What to record

Which joints you sealed, the product used, and the date, so next year's walk is a comparison. Note the doors that got new weatherstripping and the type, so replacements match. Set the fall caulk walk and a spring check of the exterior joints as recurring tasks.

Common questions

Which caulk should I use outside?

For exterior joints on siding, trim, and around windows and doors, a paintable exterior caulk (siliconized acrylic or polyurethane) that stays flexible. Pure silicone lasts longest but cannot be painted. For flues, vents, and anything hot, only a high-temperature product, and the DOE recommends leaving those to a pro. Read the tube; it says where it is rated for.

How do I know if the weatherstripping needs replacing?

Close the door on a dollar bill. If it slides out with no resistance, the seal is not touching there. Do it at several points around the door. Cracked, flattened, or torn strips have failed; strips that are intact but no longer springy have too.

Should a new house need this?

Yes, sooner than people expect. New caulk shrinks as it cures and as the framing dries, and the first year's movement opens joints that were tight at closing. A caulk walk in the first fall is normal maintenance on a new build, and cracked exterior caulk in year one is often also a builder item.

What to do next

While you are walking the exterior with a caulk gun, look down: where the ground slopes and where the downspouts discharge is the other exterior job that protects the house from water, and it is the same season. If you have irrigation, winterizing it is the third fall task on the outside of the house.