Understanding some key indicators may help you to choose better regarding your specific situation.
Repair When Possible
Still holding together: If the frames are showing any kind of surface damage, paint failure or small amounts of rot to less than 20% – restoration is often possible. An experienced evaluation will help identify if visible damage is only skin deep or structural.
Within a conservation area or on listed buildings it is preferential to retain original windows, if possible due their historical value. In many cases planning restrictions do not allow replacement; only restoration is legal. For Sash Window Repair, consider sashwindowpreservation.co.uk/services/sash-window-repair
Repair vs replacement budget: repair is 40-60% cheaper than replacement with few benefits performance wise, by draught proofing and reglazing, there are big improvements.
Replace When Necessary
Severe structural damage: When rot is over 50% of the timber, joints are failing or there has been significant compromise in the window structure, it could be less expensive to replace than repair. Restoration can be cost prohibitive – e.g. severe water damage or neglect.
New windows with glazing and weather stripping are better equipped to meet modern performance requirements, particularly if energy efficiency is a top consideration and conservation restrictions don’t apply. Windows that have had many repair attempts are good candidates for replacement unless earlier repairs were rock solid.
The Professional Assessment
Hire a reputable sash window company to give unbiased estimates. A good company will advise on repair where possible.
Making the Decision
Take into account ongoing costs as well as local planning restrictions! If you are uncertain, then repair first – you can always replace later, but original windows will never be made like that again!