Also keep in mind, there are certain requirements in juridictions for pipe diameter as a function of both distance run, and number of pipes feeding the primary line.  

Double and triple that and I get the heebie-jeebies.At the end of the day it all comes down to safety, function, and returns. 

Functional obsolescence, 40 amp fuse panel, no insulation, I love Lucy era stove?

Quite often I see people hire a General Contractor and expect them to handle the development functions.

Capex and maintenance, like others say, are a function of the condition of the property. 

In general, you would need or want a function of 2 times or more (in general) the capital demands you have gone through over last X amount of deals, in line with your business plan.  

Beyond this, the relevant cash flow metric is your Cash on Equity return - this is the amount of net cash flow the asset generates as a function of the amount of equity you have in the property, and will (generally) decrease each year as you equity increase will outpace your rent increases.

Another important reason to separate these items is that when it comes time to sell, you will be able to display to buyers clear documentation of the functions associated with your property over the period you have it.

. - If there are electric heat strips, then there could be a failure causing the electric heat to run when it isn't supposed to or that causes the electric heat to run, because the primary heat source is not functioning properly. - If there is an airflow issue in the home (collapsed duct work / dirty filter) it can cause the mechanical systems of the home to provide inefficient comfort (longer run times) while working harder to achieve comfort (higher amp draw). 

Here's what the property description says:Large remodeled brick duplex that functions as 3 units. 8.8% Cap as 3 units!