Most defects you’re likely to encounter with sash and case windows will be apparent on close visual inspection. Timber decay is one problem that's less easy to spot.
It’s usually possible to restore even the most rundown windows. Most old sash windows were made from highly durable heartwood timber of a quality that’s now difficult to find. So it makes sense to keep and repair original wood as much as possible.
Sash windows can be upgraded to improve energy efficiency.
Common causes of problems