Fire compartmentation. Three for one.

[Bert]

What’s the logic in having a one-hour firewall with a half hour fire door in it, or a two-hour firewall with a one-hour fire door?

Can fire stopping be half the FR rating of the wall in which it is installed?

Is there any guidance about this, and if there is where can I find it?  

Thanks in anticipation

[kurnal]

Because Approved document B allows it in some circumstances- see B3 and the table B1 in appendix B.
If the door is in a compartment wall separating buildings then it has to be the full fire resistance of the wall. In some other specific situations a lower standard is permitted. For protected shafts it is half the standard of the wall because any fire would have to penetrate two such doors to breach the compartment floor- one below and one above.
But your fire stopping and th epenetrations are controlled to the full standard of the wall they pennetrate.