How to deal with insurance of building when there is absentee landlord

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Usually in this case there would be a management company who would insure and bill all the landlords.

If there is no management company or if they cannot be traced there are various I understand that it should not be too difficult to create a new management company especially of there is a majority of tenants who want this.
This will entitle you to then sort out the insurance and also be in control of other communal responsibilities.

Without sorting this you would likely have a problem selling your flat as most mortgages would not be approved until this matter is sorted.

Finally, if you do not want to have the headache of speaking to the other landlords and then creating or sorting a management company, then you may decide it is worth your while to just insure the full property yourself. I do not know if you will be able to reclaim any of this cost form any of the other landlords in this case.

Good luck