Sash windows look great, but without correct draught proofing it can feel like the window is open with the amount of cold air coming in from outside (or hot air leaking outside).
Even if you had draught proofing in your sash windows at one time it is common for it to start to fall apart. Every time you slide the windows up and down it can wear away at the draught proofing or create larger gaps.
Luckily it is quite straight forward to draught proof your sash windows.
Draught proofing beads
The most common way to draught proof your sash windows is to get draft proofing sealing beans.
These go in a gap on the side of the frame. You add a glue or sealant in those gaps, cut the seals to the correct size and put them in place.
Glazing
As well as draught proofing the beads you can add more glazing. These are basically a second window behind your sash window. This creates a sealed gap between the two windows, which helps reduce draughts getting through