Caulk Around Windows: Inside, Outside and How Often

Caulk around windows seals the joints that do not move: between the window frame and the siding or trim outside, and between the frame, trim and wall inside. Outside, the sealant has to stand up to sun, rain and movement; inside, it mainly stops drafts and is usually painted. This Old House suggests polyurethane or silicone for exterior window joints and siliconized latex for interior work, and says to inspect windows yearly and recaulk every three to five years, or sooner if the caulk shows wear ¹.

Caulk is a maintenance item, not a repair for a failing window. If the joint keeps opening, the wood under it is soft, or water shows up inside even with fresh caulk, the problem is usually in the frame, the flashing or the installation, and another bead will only cover it. The sections below explain what goes where, what to leave open, and how to tell the two cases apart.

What caulk does, and what it does not

A window sits in a rough opening in the wall. The installer seals and flashes that opening, then the trim and siding cover the gap. The visible bead of caulk at the edge of the frame is the last line against water and air, not the main one. That is why a window can leak with perfect-looking caulk, and why caulk alone rarely fixes a leak that starts higher up.

The U.S. Department of Energy's Energy Saver Guide lists window frames among the places where air leaks, tells readers to look for improperly applied caulk, and calls caulking, sealing and weatherstripping one of the quickest money- and energy-saving tasks; DOE says sealing uncontrolled air leaks can save 10% to 20% on heating and cooling bills ⁶. That figure is for air leaks throughout a house, not for windows alone. Weatherstripping, not caulk, is for the parts that open; drafty windows: what to try first covers that side.

Exterior vs. interior sealant

The two jobs ask different things of the material.

This Old House also says to caulk when it is at least 45°F with no rain forecast for 24 hours, to avoid high humidity for exterior work, and to scrape off the old caulk first, because new caulk over old does not form a lasting seal ¹. Read the label on any tube for the surfaces and temperatures it is made for, and check your window maker's instructions before you use a solvent or sealant on the frame itself.

How often to redo it

There is no single interval that fits every house. Two published schedules:

• This Old House: inspect yearly, recaulk every three to five years, or when cracks or drafts show the caulk is failing ¹.
• Marvin's owner's manual for its Vivid line puts exterior caulk on an annual checklist: inspect the caulking around the outer edges of the frame, trim off any loose caulk and reseal gaps with a good quality caulk ³.

The yearly look matters more than the calendar: a joint that has pulled away on one side is due for new caulk, whatever its age.

Who is responsible for the caulk

Warranty documents treat the perimeter caulk as yours to maintain. Milgard's replacement-product warranty, effective January 1, 2026, says caulking or sealants between the window and the exterior cladding or trim are not part of the product, are not covered, and are a maintenance item that is the owner's responsibility ⁴. The same document excludes damage from applying sealant or caulk to the product itself as an alteration ⁴. Pella's vinyl warranty lists failure due to applied sealants or caulking among the things it does not cover ⁵.

Two practical points follow. Keep caulk on the joint between window and wall, not smeared across the frame or sash. And if a new window leaks in its first years, call the installer before you caulk over it, since the installer's own warranty may cover the work. Window warranties explained sets out what each kind of coverage includes.

Where not to caulk

Some gaps are there on purpose.

• Weep holes. Many windows have small openings at the bottom of the frame that let water drain out. The Department of Energy's Building America Solution Center warns that if weep holes are clogged or accidentally caulked, trapped water can build up in the frame, and suggests looking for caulk over them if none are visible ². Its guide describes removing that caulk with a putty knife, utility knife or flathead screwdriver, and notes that acetone may damage surfaces ².
• The bottom of a storm window. This Old House says never to seal across the bottom of a storm window, because trapped water can rot the sill ¹. The storm windows article covers how they drain.
• A window someone may need to climb out of. Never caulk an operable sash shut; see egress window requirements.

When caulk is hiding a frame problem

Caulk that fails again and again is usually a symptom. The National Park Service's guide to wooden windows calls moisture the primary factor in wood window decay, and suggests checking whether water is entering around the edges of the frame, then caulking those joints ⁷. The same guide describes the warning signs to look for first:

• Peeling or blistered paint near the joint, which NPS says usually marks where water is getting in, though the wood beneath may still be sound ⁷.
• Soft wood at the sill and lower corners. NPS describes jabbing an awl into the wood: sound wood lifts in long fibrous splinters, decayed wood in short irregular pieces ⁷.
• A sill that does not slope away from the house, so water sits against the caulk ⁷.

Other signs: a gap that reopens within a season, stains on the interior wall below the window, or a new window that drafts. DOE's consumer guide notes that even the most energy-efficient windows can result in a drafty house and condensation if they are not properly installed ⁸.

If you find soft wood, stop caulking and get the frame looked at. Rotted window frame: repair or replace walks through the options, and the repair or replace windows guide covers the wider decision. Caulk is one line on a longer list; the window maintenance checklist has the rest.

Questions to ask if someone else does it

• Will you remove the old caulk, or go over it?
• Which sealant will you use outside, and is it rated for the frame material and the siding?
• Will you leave the weep holes open?
• Did you find any soft wood or staining, and where?
• Is the installer licensed where you live?

If the frame turns out to be the problem, you can compare quotes from window installers for repair or replacement.

We are not affiliated with the manufacturers named.

About these figures

• ¹ Reported: This Old House on exterior and interior caulk types, yearly inspection, recaulking every three to five years, 45°F and 24-hour weather guidance, old caulk removal and storm window warning, updated May 27, 2026, checked October 26, 2026.
• ² Official record: Building America Solution Center guide on weep holes, caulk over weep holes and removing it, last updated July 30, 2025, checked October 26, 2026.
• ³ Reported: Marvin Vivid owner's manual (February 2026) annual checklist item on exterior caulking, checked October 26, 2026.
• ⁴ Reported: Milgard replacement product warranty effective January 1, 2026, on perimeter caulking as an owner maintenance item and the sealant exclusion, checked October 26, 2026.
• ⁵ Reported: Pella vinyl limited warranty exclusion for applied sealants or caulking, checked October 26, 2026.
• ⁶ Official record: DOE Energy Saver Guide on caulking, window frames as air-leak sites and the 10% to 20% air-sealing estimate, checked October 26, 2026.
• ⁷ Official record: National Park Service Preservation Brief 9 on moisture, caulking frame joints, peeling paint, the awl test and sill slope, checked October 26, 2026.
• ⁸ Official record: DOE consumer guide on drafts and condensation from improper installation, checked October 26, 2026.