You’ll need to examine the depth within your sash prior to deciding to consider retrofitting, you’ll need around a 35mm to 38mm sash, any lower than that would weaken the window. Software is rapid and simple. The sealant is pushed into the gaps round the window with a handy applicator. https://israelnkask.tinyblogging.com/details-fiction-and-sash-window-draught-proofing-79236384