How does depreciation work for older houses?

[Brooke Gibson]

Hi, I'm looking for an answer to this or links to resources since I've had a challenging time finding any. I hear that depreciation lasts for about 27 years and the amount deducted from tax can make the net income, from a buy and hold property, basically tax free.

What happens if the property is older than ~27 years? Is there no depreciation? If there is new depreciation from renovations or a new roof, how is it calculated? I can only guess that the data is recorded about when what was done and how much it is worth. Maybe a new floor in 2010, a new roof in 2012, etc. Also, these things aren't worth nearly as much as a whole house, so the depreciation would be much less. How is this figured?

I haven't yet noticed anyone talk about only buying houses that are very young so that they can take advantage of depreciation. Why not? It seems like buying new houses would be better. Thanks in advance for any info!