Floors have a life span of 10 years.

Example roof: Cost $6000 to replace. 25 year life span. $6000/25= $ 240 per year but what if it is 10 years old. 15 years useful life so your new capex should be $6000/15= $400 per year.

Carpet and floating floors have a 5 year life span.

And my relationship with my bank spans almost 3 decades.

If you have 1000 sf of flooring in each duplex. 2000sf*$6sf= $12000/10 year life span/12 months in a year = $100 per month for 1 item in a capex budget.

Roof $7500 / like span 25 years / 12 months = $25 per month.

Since my goal is long term investing, I was curious if this is a good idea because for the life span of my hold it'll still be a viable option.

Well, think you have the right idea since I've had syndications (i.e. larger deals with limited life span like 5-7 years) do this for the upfront cash flows.For smaller guys, between depreciation and mort int, they usually have enough tax shelter to cover income from the get go until 5 years down the road, so cost seg / accelerate depreciation doesn't get them that much more beyond a carry-forward cover on income.

Real estate over 10 year spans almost always go up in value.

I too, have utilized this strategy however I do not own and chose to rent so I utilize a commercial line of credit (CLOC) on my RE assets and my interest is not calculated on average daily balance over the span of an entire month but rather on a rate/365 days daily basis.