A colleague of mine had this to add about the advantages of repair over
replacement: Sash made from plantation-grown wood is lacking in extractives
(natural pesticides) compared with sash from old growth timber. As well, the
grain is much looser. New wood is also mainly sapwood, vs. heartwood, and is
inherently more vulnerable to attack.

On another point, I suppose that the new materials used in repair of old
sash are just as susceptible, whatever the reason, to host bug and fungi
fests. This points up the need for careful detailing and good old
unglamorous maintenance.

Forever yours,

Dopple hung.