Placed in service 8/17/15.  House basis, net land 50,215; Land 16,534.  Using supporting article by Withum (article cites IRS approval & example is replacing a roof) & Fed website for Producer Price Index to address valuations. https://www.withum.com/resources/the-basics-of-partial-asset-dispositions/

Here is the crux.  How do I make Asset Entry worksheet "accept/acknowledge" decrease in basis for old roof portion torn off? I was able to do a Casualty Loss for $6057 cost attributable to old roof (e.g. FMV before event) less FMV after event $1427 which squeezed my calculated loss figure of $4630 on F4797, line 14 as a loss from F4684.  However this is an ordinary loss and the roof is a capital asset (right?)

For the new replacement roof (2024), I imagine I have to begin its 27-1/2 yr depr in '24 and not try to "add it to the original basis" when it was placed in svc in 2015