Can’t stress understanding zoning laws enough…I tried this and found out it was a requirement to have a firewall, and each unit has to have two exterior doors.

I've seen houses sell FHA with sill plate issues, or firewall issues, etc.

We are going to buy a home that has a carriage house (on the parcel) and I was curious how I could firewall the liability if something were to happen in the onsite rental .... 

However, in examining the heaters it was noticed that our plans on double wall noise abatement, is causing problems with any electrical outlets on the adjoining walls.In the past we'd put up the fire wall between the two walls, but this GC thought that was wasteful since we'd have to drywall both sides of the wall and the center divider.

@Ronald RohdeDoes the partition need to be a fire wall?

If you have a separate unit, you have to have a firewall.

If the Mortgagee is unsure whether the Property has been completed for at least one year, the Mortgagee must request a copy of the Certificate of Occupancy (CO) or equivalent.A Property that is not eligible for a 203(b) Mortgage due to health and safety or security issues may be eligible under 203(k) if the rehabilitation or repair work performed will correct such issues.A Property with an existing 203(k) Mortgage is not eligible to be refinanced until all repairs are completed and the case has been electronically closed out.The following property types may be financed:a one- to four-unit Single Family Structure;an individual Condominium Unit, meeting the following requirements:    the unit must be located in an FHA-Approved Condominium Project and must comply with all other requirements for condominiums;    rehabilitation or improvements are limited to the interior of the unit, except for the installation of firewalls in the attic for the unit;    no more than five units per Condominium Association, or 25 percent of the total number of units, whichever is less, can undergo rehabilitation at any time; and    after rehabilitation is complete, the unit is located in a Structure containing no more than four units.

Assuming the concrete is the firewall between next house.

Thats the key really,,Is The Guy Accessable,,,or is there "A Firewall" between you and him...even after you give "The Guy " what he wants,,,,i.e.

I don't tell them I'm the owner as a firewall between my business and my personal life.Caveat: I would do everything in my power to use this position as a force for good and not manipulation.