Whether Municipal Planning, Building and Zoning are separate segments of Municipal Land Use Laws, or all 3 are segments of an all-inclusive Zoning & Use law, if a municipality requires a building permit and/or certificate of occupancy for either a 1 room addition or conversion of an existing patio, deck, porch, or garage into GLA, or a new addition of an accessory dwelling unit or conversion of any of the above into an accessory dwelling unit - either the expansion or conversion complies with Municipal Building and Use Codes or it does not. The OP stated "without a permit" - indicating that the specific Municipality where the subject is located requires one for the conversion cited. It is either legal, LNC, or illegal. Ilegal use applies under Municipal Ordinance and Fannie Requirements. Under Residential Zoning, Residential Use of the Site remains permissible, the Site Improvement represents an Illegal Use.
example: A building permit is required for any work that physically changes or adds structures to your property. There are many exemptions from building permits, so telephone (760) 602-2717, (760) 602-2718 or (760) 602-2721 to inquire as to whether a permit is required before beginning your project or check the Carlsbad Municiple Code, CMC 18.04.105.
Zoning Code
Chapter 21.10 R-1 ONE-FAMILY RESIDENTIAL ZONE*
21.10.010 Intent and purpose.
21.10.020 Permitted uses.
21.10.030 Second dwelling units.
21.10.030 Second dwelling units.
A. The public good is served when there exists in a city housing which is appropriate for the needs of and affordable to all members of the public who reside within that city. Among other needs, there is in Carlsbad a need for affordable rental housing. Therefore, it is in the public interest for the city to promote a range of housing alternatives in order to meet the affordable rental housing needs of its citizens. This section is intended to provide a rental housing alternative by establishing a procedure to create new second dwelling units.
B. The provisions of this section shall apply to single-family zones R-A, R-E and R-1, areas designated by a master plan for single-family detached dwellings in P-C zones and lots within multifamily zones R-2, R-3, R-P, R-T, R-W and RD-M, which are developed with single-family residences.
C. Second dwelling units developed within the coastal zone require a minor coastal development permit issued according to the provisions of Section 21.201.085 and a building permit. Second dwelling units outside of the coastal zone require a building permit.
D. The completed minor coastal development permit and/or building permit application for a second dwelling unit shall include the following information:
1. The name(s) of the owner(s);
2. The address of the dwelling units;
3. The assessor’s parcel number;
4. Building elevations and a general floor plan of the second dwelling unit;
5. A scaled drawing showing the lot dimensions, the location of the primary and second dwelling unit, location of all vehicular parking and the total square footage of both units;
6. Description and location of water and sanitary (sewer) services; and
7. An applicant-signed affidavit of compliance declaring that: (a) the second dwelling unit is not in conflict with existing conditions, covenants and restrictions (CC&Rs) applicable to the title of the subject property; (b) the property owner(s) shall reside in either the main dwelling unit or the second dwelling unit unless a lessee leases both the main dwelling and the second dwelling unit; (c) the property owners agree to rent the second dwelling unit at a monthly rental rate which shall not exceed an income of a low-income household, adjusted for household size, at eighty percent of the San Diego County median income.
E. Second dwelling units shall comply with the following:
1. The second dwelling unit shall either be attached to the main dwelling unit and located within the habitable area of the main dwelling unit or detached from the main dwelling unit and located on the same lot as the main dwelling unit;
2. The second dwelling unit shall have a separate entrance;
3. The second dwelling unit must meet the setback, lot coverage and other development standards applicable to the zone which are not addressed within this subsection. In the coastal zone, any housing development processed pursuant to this chapter shall be consistent with all certified local coastal program provisions, with the exception of density, or as otherwise specified within this subsection;
4. Attached second dwelling units shall conform to the height limits applicable to the zone and detached second dwelling units shall be limited to one story, except that second dwelling units constructed above detached garages shall be permitted and shall conform to the height limits applicable to the zone;
5. Garage conversions are prohibited unless replacement off-street garage parking is provided concurrently and in compliance with the requirements of Chapter 21.44;
6. Second dwelling units shall not be permitted on a lot or parcel having guest or accessory living quarters, or a residential care facility. Existing guest or accessory living quarters may be converted into a second dwelling unit provided that all zoning and structural requirements are met;
7. One additional paved off-street (covered or uncovered) parking space shall be provided for the second dwelling unit and shall comply with the requirements of Chapter 21.44. The additional parking space may be provided through tandem parking (provided that the garage is set back a minimum of twenty feet from the property line) or in the front yard setback;
8. Adequate water and sewer capacity and facilities for the second dwelling unit must be available or made available;
9. All necessary public facilities and services must be available or made available;
10. The second unit may be rented and shall not be sold separately from the main dwelling unit unless the lot on which such units are located is subdivided. The lot upon which the second unit is located shall not be subdivided unless each lot which would be created by the subdivision will comply with the requirements of this title and Title 20; and further provided, that all structures existing on each proposed lot will comply with the development standards applicable to each lot;
11. The total area of floor space for an attached or detached second unit shall not exceed six hundred forty square feet;
12. The second dwelling unit shall be architecturally compatible with the main dwelling unit, in terms of appearance, materials and finished quality;
13. A second dwelling unit which conforms to the requirements of this section shall be allowed to exceed the permitted density for the lot upon which it is located and shall be deemed to be a residential use consistent with the density requirements of the general plan and the zoning designation for the lot;
14. The size of the lot upon which a second dwelling unit is proposed shall not be less than the minimum lot size required of the zone. (Ord. NS-718 § 7 (part), 2004)
http://www.bpcnet.com/codes/carlsbad/_DATA/TITLE18/Chapter_18_04_BUILDING_CODE.html#18 Building Code
18.04.310 Violations.
Any person or corporation who violates any of the provisions of this code or this chapter is guilty of an infraction, except for the fourth and each additional violation of a provision within one year, which shall be a misdemeanor. Penalties for a
violation of this chapter shall be as designated in section 1.08.010 of this code. (Ord. NS-333 § 2 (part), 1995)