Amazing duplex... but it is zoned single?

[Jon Huber]

In an area of where most duplexes are comping around $250k+, and the singles around $150k+... I found a beautiful duplex priced $185. I did some digging and the property is zoned for a single. However, I am still interested, as the duplex is "grandfathered" in. I understand if it burns down, I am out on my duplex, but it will have good cash flow until it does.

My question... how much of a percentage do I take off from the comps because it's zoned single? Or should I just stay away all together?