The economy seems to be on a slow and steady upward climb.  

If discovered, not only do you risk fines and litigation, you'll be forced to tear it down, insurance rates climb and you'd be criminally liable for any injuries on that space (think Oakland warehouse fire).  

Bought right before prices started climbing in Vallejo.

I'm past climbing onto roofs & into attics to find issues like bathrooms vented into the attic & the resultant mold accumulation.

http://www.har.com/content/newsroom/Houston Real Estate Highlights in January: Single-family home sales rose 8.9 percent year-over-year, with 4,469 units sold;Days on Market (DOM) for single-family homes increased slightly from 65 days in January 2017 to 67 days this January;Total property sales increased 8.7 percent with 5,468 units sold;Total dollar volume climbed 6.3 percent to $1.4 billion;The single-family home median price rose 3.8 percent to $218,000, which represents a January high;The single-family home average price declined 2.1 percent to $270,303;Single-family homes months of inventory was unchanged year-over-year at a 3.3-months supply;Townhome/condominium sales fell 1.3 percent, with the average price up 2.1 percent to $192,918 and the median price up 13.6 percent to $159,000;Leases of single-family homes rose 1.9 percent with the average rent up 1.4 percent to $1,748;Volume of townhome/condominium leases fell 5.3 percent with average rent up 1.3 percent to $1,516

You make money when market rate for rents appreciate so when you appropriately raise rents as the market rent climbs that's how you accumulate money while your mortgage is constant it never changes.

Rents have been climbing pretty quickly around here, and $1500/month wouldn't be unheard of. 

Values will not climb for ever and when they turn there will be a lot of appreciation speculators wishing they had taken their pot of gold when they could.

Even if the property loses a lot of value in the short term and your net worth drops, you will still have your cashflow and it is very likely that it will eventually climb back up based on previous markets.

Great area for a rental and should expect to see prices climb a bit in the next couple years.