Debbie Rose knows what she is saying here. Also, it depends on what kind of business. North Jersey is densely populated and a great tolerance exists for mixed use streets. Land use Zoning is how towns protect values, keeping residential just that. A normal residential street that allows a business to start up next to residence would be unusual on the face of it. Perhaops it has always been permitted and no one noticed? As a genral statement, I believe any appraiser would tell you the effect of new business use on the neighboring residential value would be negative, but how much is dependent on a lot of factors. I can give you an excellent reference of an appraiser how would likely chat about it at no charge giving you some ideas. See profile for email contact.