Value models - Fixed Assets

I am trying to understand the reason of value models for fixed Assets.

I have for example a fixed asset which is depreciated on a straight line for 30 years.

On this asset I have certain additions/acquisitions every 5 years, and these additions need to be depreciated for 5 years.

So I am thinking to deal with this as follows:

1. Create a new value model with 5 years depreciation period
2. When these additions occur, record an acquisiion on this new 5 year value model
3. In this way I will have the initial asset depreciate for 30 years (as per another value model) and the additions for 5 years (as per the new value model).

It this a right way to use the value models for the fixed assets?