Is building components depreciation 20%?

[Harpreet Singh]

Hi folks, 
As we know residential depreciation is 2.5% (cost of building/27.5) and commercial real estate depreciation is 3.6% (cost of building/39).
Is it true that components(contents, landscaping, improvements etc.) related or tied to the building have depreciation of 20%  of cost of components of building.

For example:
If we purchase a residential building for 800k and 200k is land cost then building structure for depreciation equals 600k.

Further out of 600k, the total cost of components which depreciate faster may cost 50k (may be 100k or something else but I am not expert in that). So now here is our depreciation calculation :
(550k x 2.5/100) + (50k x 20/100) = 23,750

I have heard and seen many people, CPA's or tax filers don't do it.
I am really impressed with 20% components part.