Because if my house burnt down, I'd expect it to be rebuilt with the same
patterned brick and wooden sash windows

P.S. Other things that might apply

(a) Chances that asbestos will be discovered, making demolition more
expensive.
(b) Problems with planning/conservation issues.
(c) Possible greater fire risk (won't affect rebuild cost, but might affect
premiums).
(d) Use of proper roof structure, rather than cheap trussed rafters.
(e) Use of more expensive materials, such as real slate on roofs.
(f) Requirement for more highly skilled crafts.

Christian.