Yesterday we removed 2 old aluminium sliding windows (the original timber frames were still hidden behind them and also had to be removed).
We kept the internal linings, nosing and aves as they were in good condition and there was no need to replace them. But more care is required when removing the existing frames so as to not damage those internal timbers.
We replaced them with new cedar single hung windows. Dummy side sashes (they dont move). Locks, screen and operated with spiral balances (black tubes that hold the sash up and down – as opposed to weights and pulleys in a box frame window (we we also make).