Owners of flats pay a service charge alongside any mortgage, and the amount can change substantially between years. What it buys is the building everything else sits inside.
The charge covers what nobody owns individually
A block is divided into flats and common parts, and the common parts belong to the building rather than to any resident.
Roofs, structure, entrance halls, lifts, stairwells, drainage and external walls all have to be maintained by someone, and the service charge is how that is funded.
Insurance for the structure sits in the same category, since a single flat cannot sensibly insure the building it forms part of.
Day-to-day costs are the visible part
Cleaning, lighting, gardening, lift maintenance and communal heating recur predictably and make up the routine budget.
Management fees are charged on top, covering the administration of contracts, accounts, correspondence and statutory compliance.
These items are the ones residents see, and they are rarely the reason a charge rises sharply in a particular year.
Major works drive the large increases
Roofs, lifts, windows and external redecoration are replaced on cycles measured in decades, and each is expensive when it arrives.
Many buildings collect a reserve fund so the cost is spread across years rather than falling on whoever happens to own a flat when the work occurs.
Where no reserve exists, owners face a single large demand, and the timing of a sale relative to that demand becomes a significant financial event.
Apportionment is where disputes start
Each flat pays a share defined in its lease, which may be equal, or based on floor area, or on an allocation set when the building was converted.
Whether a facility benefits every flat is frequently contested, particularly lifts, car parks and grounds that only some residents use.
Because the shares are written into leases, changing them usually requires agreement from all parties, which is why an apportionment widely regarded as unfair can persist for decades.
Consultation and challenge follow a process
Most jurisdictions require leaseholders to be consulted before large works or long contracts, with a set procedure and defined periods for comment.
Charges must generally be reasonable and properly incurred, and there are routes to challenge them where they are not.
Managing agents are also expected to account for what has been spent, and owners can normally ask to inspect the invoices behind a year's figures.
The details differ by jurisdiction and change over time, so the lease and the applicable local rules are the starting point for anyone questioning a demand.