A drafty window is really a set of possible leaks: between sash and frame, between frame and wall, through failed glazing, or straight through cold single-pane glass. Each has a different fix, a different cost, and a different honest prognosis.
Before you spend on either repairs or replacement, run through this diagnostic — it's the same logic we apply during in-home assessments.
Locate the leak precisely
On a windy day, move a lit incense stick or a damp hand slowly around the window: along the sash edges, at the meeting rail (where double-hung sashes overlap), around the frame perimeter where it meets the wall, and at the sill. Note exactly where air moves — the location tells you the fix. Also lock the window while testing: an unlocked double-hung or casement isn't fully seated in its weatherstripping, and many "drafts" are just unlocked windows.
Fixes that genuinely work
Matched to the leak location:
- Sash-edge drafts → replacement weatherstripping (V-strip, fin, or compression types depending on window style); cheap and effective when the sash still fits square.
- Frame-to-wall drafts → remove interior casing, fill gaps with low-expansion foam or backer rod, re-caulk exterior perimeter; fixes the installation, not the window.
- Meeting-rail leaks on double-hungs → adjust or replace the sash lock so it pulls the rails tight together.
- Glazing rattles on old wood sashes → re-putty loose panes; stops both drafts and rattle.
- Overall cold from single-pane glass → interior shrink film or storms help seasonally, but you're managing the problem, not solving it.
The drafts you can't fix
Repairs stop working when the window's geometry has failed: rotted frames or sills, warped or shrunken sashes that no longer meet their stops, worn-out balances that let sashes drop, or frames racked by settling. You can chase these with ever-thicker weatherstrip, but the gaps move and reopen. If the glass itself is failed (fogged double-panes) or single-pane, the thermal problem goes through the window, not around it.
A simple decision rule
Fix when: the window is structurally sound, the glass is intact, and the leak is localized weatherstripping or perimeter sealing. Replace when: there's rot, racking, failed glass, single-pane construction, or you're re-fixing the same window a second time. Age is the tiebreaker — money into a 30-year-old builder-grade window rarely makes sense when replacement resets everything with a warranty.
JMB Builders gives honest fix-vs-replace assessments across the Twin Cities metro — free in-home estimates at 763-204-2099.
