San Diego has a significant housing shortage and is geographically constrained.  

In growing cities like Las Vegas, land shortage combined with rapid population growth and continuing large capital inflow mean that the appreciation rate will be much higher than the national average. 5% is a conservative estimate.

A house with an ADU does not become a duplex, it's a house with an ADU.Hey Tony,I would say you have been getting mix responses because adding an ADU to a 4 unit is uncommon.If we look at this from a property development perspective most major cites and California law support building additional units because of the shortage of housing.Lenders who have not caught up yet with financing on multifamily with ADU’s would be your challenge when it comes to appraisal.I think I would look at it this way, if in the short run building the ADU adds enough value to the property aside from appreciation then it might make sense.

I would check out one of the recent releases 153: HousingWire CEO: This Inventory Shortage Could Last Decades w/Clayton Collins as I think this episode would provide insight on what markets may see the biggest price reductions!

I know there is a severe shortage on the availability of long term rentals.   

There is a rental shortage in the area. 

There is a housing shortage and I suspect it will continuously get easier to add units. 

Our residential real estate market is suffering from an inventory shortage as is much of the country.

It is probably a little more difficult to find renters, but there's no shortage of renters.

We're all experiencing terrible inventory shortages.