The depreciable amount of all fixed assets including buildings but excluding freehold land, are depreciated on a straight-line basis over the individual asset's useful life from the time the asset is held ready for use. Leasehold improvements are depreciated over the shorter of either the unexpired period of the lease or the estimated useful life of the improvements.
Major depreciation periods used for each class of depreciable asset are:
| Buildings | 30 to 50 years |
|---|---|
| Furniture and Equipment | 4 to 10 years |
| Plant and Equipment | 5 to 15 years |
| Sealed roads and streets | |
| formation | not depreciated |
| pavement | 50 years |
| seal | |
| - bituminous seals | 20 years |
| - asphalt surfaces | 25 years |
| Gravel roads | |
| formation | not depreciated |
| pavement | 50 years |
| gravel sheet | 12 years |
| Formed roads | |
| formation | not depreciated |
| pavement | 50 years |
| Footpaths - slab | 20 years |
| Sewerage piping | 100 years |
| Water supply piping & drainage systems | 75 years |
The assets residual values and useful lives are reviewed, and adjusted if appropriate, at the end of each reporting period.
An asset's carrying amount is written down immediately to its recoverable amount if the asset's carrying amount is greater than its estimated recoverable amount.
Gains and losses on disposals are determined by comparing proceeds with the carrying amount. These gains and losses are included in profit or loss in the period which they arise.