Under IAS 23, borrowing costs that are directly attributable to the acquisition, construction, or production of a qualifying asset must be capitalised as part of that asset's cost — expensing them is not permitted (IAS 23.8).
The IAS 23 Qualifying Asset Definition is the gateway to the entire capitalisation regime. An asset qualifies only when it necessarily takes a substantial period of time to get ready for its intended use or sale (IAS 23.5). There is no bright-line threshold in the standard; judgement is required, though practice commonly treats periods exceeding 12 months as substantial.