It's a tough choice predicated on the idea that cost is an issue. All factors being equal, it's likely that most homeowners would choose replacement over repair. But cost is the factor that turns this into a true dilemma. With new windows costing between $300 to $2,100 or more installed, an entire house of new windows can end up costing several thousand dollars.
Repair seems to be the likely avenue then—except that repair isn't always possible with most modern windows. Older, single-pane windows were simple to fix. By contrast, double- or triple-pane sealed windows are more difficult to repair. In some cases, repair isn't even possible.
So, when can or should you repair or replace your windows?
Cracked or broken glass (replace sash)
Broken muntins/mullions on single-pane windows
Slow-moving or stuck window sashes
Missing or damaged exterior drip cap
Poor exterior window casing
Minor water leaks
Foggy windows with inside condensation
Poor interior faux muntins/mullions
Major water leakage
When to Repair Your Window
Cracked or Broken Glass
Safety and visual acuity play into the decision to replace a window when the glass is bad. Single-pane windows can be effectively and inexpensively repaired by the homeowner or a glazier.
When a multi-paned glass is broken or cracked, look into sash replacement. But if you have been tolerating window problems for a long time, this might be a good excuse to replace the entire window.
Broken Muntins or Mullions
Rotting or split muntins and mullions that hold glass in single-pane windows must be rebuilt. Those with missing or brittle putty holding the glass panes in place can easily be fixed. After removing the glass and scraping the area clean, you would apply fresh putty and then secure the glass with new glazier's points.
Balky or Stuck Sashes
One typical problem of older windows is upper or lower sashes which are unable to move. This could be due to multiple layers of paint bridging the sash and frame, holding the two together. Or the sash might have come off track.
When sashes are hard to raise, the cause is usually broken cords on sash weights. For spring-type sashes, the spring may have failed or come loose, and this type of problem can be fixed.
Missing or Rotting Drip Cap
The drip cap is the exterior shield at top of the window. This is an easy repair that most do-it-yourselfers can perform. Rot-free, rust-free aluminum drip caps can be purchased at nearly all home centers, nailed into place, then caulked.
Poor Exterior Window Casing
Loose, cracked, rotting, or missing exterior casing is unattractive and can lead to window damage. Damaged casing alone does not entail window replacement.
Primed wood exterior casing can be found at most home centers. Homeowners can remove the existing casing and replace it with the new casing. Remember that primed wood is not weather-resistant. It should be painted quickly after installation with exterior-grade paint. Low maintenance vinyl and PVC products are also available for this application.
Minor Water Leakage
When interior water is detected near the window area, often it is coming from around the window, not through the window.
Poorly draining gutters and drainpipes can force water towards windows. Window seals are meant to hold back water, but not water of such great force. Re-route your drainage system and see if this makes a difference.
When to Replace Your Window
Foggy windows are caused by water condensing inside of your window's double-paned or triple-paned insulated glass unit (IGU).
Today's windows have these self-sufficient IGUs built into them. So, unlike multi-paned windows of the past, which had the glass set into place by a glazier, IGUs are sealed and permanent. A do-it-yourselfer or even a competent window technician can't disassemble an IGU and rebuild it. Removal and replacement is the only option.
What this means for the owner of fogged-up windows is that IGUs are generally an all-or-nothing project. At the very least, In some cases, individual IGU window panes can be ordered from a glass company and replaced.
When the outer structure of the window is failing, it's time to buy a new window. In some cases, the area around the window may be in poor shape, too: studs, house sheathing, siding, and insulation.
This warrants both replacing the window and rebuilding parts of the wall. In this case, you'll be using a new-construction window, not a replacement window.
Major Water Leakage
Excessive water infiltration around the window might mean that your exterior window casing is bad. This isn't so much a window issue as it is an issue to do with your exterior as a whole. But if water does prove to be coming through the window, this is probably time to start shopping for new windows.
Broken Faux Muntins or Mullions in IGUs
Muntins and mullions are the pieces of wood separating panes of glass. If these are faux muntins and mullions, set between two panes of glass for effect only, they cannot be replaced. The good news is that they will not affect your window's functionality.