This question seems to come up a lot on the BP forum.

Here is the step-by-step instruction how I got variance for SFH zoning to be used as a duplex with the budget and time schedule

• 1)Zoning application. Fee is $25.00 Applied on 03/02/2017
• Application can be found here https://business.phila.gov/media/Zoning-Use-Registration-Permit-Application.pdf but it is better to go to L&I and do the application with an agent together
• 2) You WILL get a notice of refusal aka denial. City refuses every single application. Got it on 03/29/2017
• 3)Now we need to file for appeal. The link for the application form: https://www.phila.gov/li/PDF/Code%20Bulletins/applicationZBA%20appeal2013.pdf where you will need to explain how compliance with current zoning code causes you unnecessary hardship as well as in the even you get the variance how it will effect your neighbors and the neighborhood (traffic congestion, parking issues, excessive noise etc.). To file for the appeal you will also have to attach your tax compliance certificate which you can get from https://secure.phila.gov/revenue/TaxCompliance/ Appeal fee if $125.00. Filed on 04/08/2017
• 4)You will be scheduled for the board hearing and provided with yellow (bright orange) posters for the property. Plus you will be given detailed information that you will need to follow in order to get ready for the hearing. I didn’t find detailed instructions online, however there is simpler version on L&I website: http://www.phila.gov/li/Pages/Appeals.aspx Orange posters will have to be posted at the property and be easily visible and readable for people. My hearing was set for 06/20/2017
• 5)You will need to schedule a meeting with an RCO (registered community organization) and present your case to them. It’s basically local zoning board. You want to get a few neighbors at the meeting who will agree to your proposed use and vote for it. You will need to get a letter from local RCO with their decision and vote registration that you will need for your maim hearing.
• 6)Before your RCO meeting, You will be given a special letterform that you will need to deliver to all residents within couple blocks radius. You will be provided with the list of addresses. This letter will include description of your proposed use and time, date and place of the local meeting. I had 139 addresses. $98 for post stamps.
• 7)After I complied with all requirements, I had to make photos of the property. You will have instruction on how to make photos and what size. Also I had to make accurately drawn, scaled and fully dimensioned site plans and floor plans. Did it myself, no cost. Used online design software https://www.homestyler.com/
• 8)When at the ZBA meeting you will present your case in front of a few zoning board members. Everything goes pretty quickly. They will hear a lot of appeals the same time. You will be called by the address. I was the very last in the list so heard all other presenters. Most of the appeals were approved. ZBA denies right away any appeal if any neighbor shows up and protests against your proposed use or in you have a denial letter from your first RCA meeting. I got approved. They will give you a notice of decision. Then you will need to wait until you receive the notice in the mail (until they process it and put in the system). I got the notice in the mail on 07/10/2017
• 9)With the notice you will go to the L&I and apply for (aka pay for) use permit and receive it right on the spot. $125 fee
• 10) When you have yore use permit in hands you can go and apply for rental license. $55 per unit. $110 in my case.
• 11) Total damage: $483.00 and 4 moths. DONE

Hope this helps. 

Feel free to reach out if you have questions. I would assume if you use an attorney your cost might significantly go up.