Drafty windows are one of the biggest sources of energy loss in homes throughout the DC, Virginia, and Maryland area. Air leaks around windows account for up to 30% of heating and cooling costs. This guide shows you how to identify leak sources, choose the right sealant for each joint type, and properly apply caulk, weatherstripping, and glazing compound to create an airtight, weatherproof window seal that lasts for years.
Last Updated: March 2026
On a windy day, hold a lit incense stick or thin ribbon near window edges, where the glass meets the frame, along the sash joints, and around the frame-to-wall junction. Air movement will deflect the smoke or ribbon, pinpointing the leak location. Common leak points include: the junction between the glass and the sash (failed glazing), where the sash meets the frame (worn weatherstripping), and where the window frame meets the wall (failed exterior caulk).
For the glass-to-sash joint, use glazing compound (wood frames) or silicone sealant (metal and vinyl frames). For the sash-to-frame joint, use self-adhesive weatherstripping (V-strip, foam, or rubber compression). For the frame-to-wall exterior joint, use paintable acrylic-latex or silicone caulk. Never use silicone caulk where you need to paint later -- it will not accept paint. For interior trim gaps, use paintable latex caulk.
Peel away old weatherstripping by hand. Remove old caulk with a utility knife and caulk removal tool, cutting along both edges and pulling the bead free. Scrape any remaining residue with a plastic putty knife. Clean all surfaces with isopropyl alcohol to remove oils and dust -- sealants bond poorly to dirty surfaces. Allow surfaces to dry completely before applying new sealant. In the DMV area, choose a dry day with temperatures between 40-90 degrees F for best adhesion.
For double-hung windows, apply V-strip (also called tension seal) weatherstripping along the channels where the sash slides. For casement windows, apply compression weatherstripping (rubber or foam) around the sash perimeter where it contacts the frame when closed. Cut the weatherstripping to length and press the adhesive side firmly into the clean channel. The strip should compress slightly when the window is closed to create a seal without preventing the window from operating.
Cut the caulk tube tip at a 45-degree angle, creating an opening slightly smaller than the gap you need to fill. Apply a continuous, even bead along the exterior junction between the window frame and the wall siding or brick. Also caulk any gaps in interior trim. Use steady, even pressure on the caulk gun and move at a consistent speed. Smooth the bead with a wet finger or caulk tool within 5 minutes of application, before skinning begins.
For older wood-frame windows where the glazing putty has cracked or fallen out, remove the old putty, press new glazing compound into the rabbet, and smooth it at a 45-degree angle with a putty knife. This seals the glass to the sash and prevents both air leaks and water infiltration. Allow 7-14 days for curing before painting. For modern vinyl or aluminum windows with rubber gaskets, replace any cracked or compressed gaskets.
After all sealants have cured (24 hours for caulk, 7-14 days for glazing compound), repeat the incense or ribbon test at all the leak points you identified earlier. You should notice a significant reduction in air movement. For a more precise test, close all windows and doors, turn on the kitchen and bathroom exhaust fans, and repeat the test -- the fans create negative pressure that amplifies any remaining air leaks around windows.
For sealing the glass-to-frame joint, 100% silicone sealant provides the best long-term performance -- it remains flexible for 20+ years, withstands extreme temperatures, and is waterproof. For the window frame-to-wall joint that needs to be painted, acrylic-latex caulk is the best choice because it accepts paint and is easy to tool. For glazing wood-frame windows, traditional linseed oil putty or modern acrylic glazing compound are the appropriate materials. Avoid using silicone where you will need to paint, and avoid latex caulk for glass-to-frame joints because it becomes brittle.
Exterior caulk should be inspected annually and resealed every 5-10 years, depending on sun exposure and caulk quality. Weatherstripping typically lasts 3-5 years for foam types and 5-10 years for rubber and V-strip types. Glazing compound on wood windows can last 15-20 years in ideal conditions but should be inspected every 5 years for cracking. In the DC, Virginia, and Maryland area, the combination of hot summers, cold winters, and humidity puts significant stress on window seals, so annual inspection is worthwhile.
Sealing from the inside alone is partially effective for reducing drafts but does not address exterior water infiltration. Interior weatherstripping and caulking around trim can significantly reduce air leaks. For a temporary boost, window insulation film (heat-shrink plastic applied to the interior frame) creates a dead air space that reduces heat loss by up to 40%. However, for a complete seal that handles both air and water, exterior caulking at the frame-to-wall junction is essential.
A failed insulated glass unit (IGU) seal -- indicated by fog or condensation between the panes -- cannot be effectively fixed with external sealants. The seal failure has allowed moist air into the space between the panes, and the desiccant in the spacer bar is saturated. The only proper repair is to replace the insulated glass unit. Some companies offer defogging services that drill holes in the glass to remove moisture, but this only removes the current moisture and does not restore the insulating gas fill or repair the seal.
Most caulks and sealants adhere best when applied at temperatures between 40 and 90 degrees F (4 to 32 degrees C). Below 40 degrees, sealants become stiff and difficult to tool, and adhesion to cold surfaces is poor. Above 90 degrees, sealants may cure too quickly before you can smooth them. The ideal conditions are 50-70 degrees F with low humidity and dry surfaces. In the DMV area, spring (April-May) and fall (September-October) provide the best window sealing conditions.
Yes, significantly. The Department of Energy estimates that air leaks around windows account for 25-30% of heating and cooling energy use in a typical home. Properly sealing windows with caulk and weatherstripping can reduce your heating and cooling costs by 10-15%. In the DMV area, where winter heating and summer cooling are both significant expenses, sealing windows is one of the most cost-effective energy improvements you can make -- the materials typically cost under a few dollars per window and pay for themselves within one heating season.
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