The only option is to do a cash out refinance.They all made the caveat and distinction that if it is just a "second home" which I rent out for air b'n'b or otherwise, then they can do a HELOC with the better rates. 

An important distinction here, Management Companies/PM's/Account Executives, whatever title is used, they do NOT typically have the authority to make major decisions or expenditures.

When HPRs are created isn't the original lot ownership divided into two new distinct lots? 

To create a completely separate basement renal unit up to code is fairly difficult in fair fax county, slightly less difficult in Montgomery county, and much more straight forward in DC.But, if you’re only going to be there for a year, you could live in the basement, not completely separate it (thus attempting to establish two distinct units) and then after moving out rent the whole house or rent by rooms individually.I would probably look close to falls church / arlington for proximity to DC and also IAD, close enough to transit lines, and a good prospect for appreciation.

The most important distinction is that there are very few opportunities to add value to a NNN investment when compared to a single-family home due to the fact that once a tenant is in place, there is very little left to do.

Very distinctive.

The point I was making was not to draw a distinction between new and existing construction but was based on the fact that in general, a title insurance policy only indemnifies the Insured against loss or damage caused by matters recorded in the public records of the county where the property lies. 

So asking "how should an ADU be valued" might need a little more distinction before judgment. 

You have two very distinct advantages..1.

This is the main distinction between multifamily and single family and can be expensive either up front or in the long-term if you manage a shared utility environment.Hope that helps.