if the chip is in a socket you may be able to replace it
if soldered to the board, default the system & reprogram, decent battery & 1313 may help
if your break it completely there probably another pcb on fleabay
you doing a wanky "grand design" project ?
I'd assume you need either need mains powered interlink smoke detectors or bs 5839 pt1 fire alarm
normally somebody with an understanding of construction & buildings regulations like a competent architect would have advised or taken advice on whats required ?
err..have'nt interlinked mains powered smoke alarm been a requirement for new builds for the last 25yrs or so ?
Looking at there site its does'nt appear to confirm to any std ?
Is the property wired & plastered yet ?