They are common for years in other parts of world (I see many in Europe where the heating is often primary radiators (no ducting) with Splits providing supplemental heat and AC). 

Currently I started with buy and holds in order to supplement and then eventually replace my job income.

I currently own a home with an apartment that I rent out to help supplement income.

I have recently been learning about and been interested in investing in real estate to supplement my income or possibly do full time as a career change.

I'm considering investing money in different avenues, and one being the purchase of a Subway franchise to supplement income.I have always had subway on my mind, and I feel now, given all things, it wouldn't be a bad idea. 

However, since retirement planners say you should plan for 30+ years of retirement, I see RE as a great way to supplement my retirement down the road.Brian

These jobs will not only be educational, but it will provide income to supplement your living and investments, and most importantly, make it easier to get financing.

I'd like to supplement my income with monthly cash flow from the properties at the same time building equity in all of the homes that I own. 

We eventually paid $60,000 to install a supplemental AC system just for our suite.As a property manager I love it.

I'm looking to supplement my income by building a rental portfolio then eventually replace my income and retire early in 5-6 years.