An overage clause (also called uplift clause or, more appropriately in our view, claw-back clause) on a property for sale, means in essence that if there is future development, then a buyer must pay a percentage on any increase in value to the previous seller.
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Some overage clauses can cover 25-50% of the increased value, and be in place for 25yrs, or longer.
We don’t believe there is an equivalent in other contexts, where it is contractually legal for a previous owner to demand a share of future values in something they no longer own!
As a parallel – if one were to buy a regular van and convert it to a luxury camper – would the original owner ask for a share in the uplift in value of the transformed vehicle?