Even if ADU's become an allowed use in Honolulu, Building Code compliance will be a major hurdle for many existing structures that wish to convert a space into an ADU.
San Francisco is also grappling with a housing shortage and numerous illegal dwelling units. According to a Report by the San Francisco Planning & Urban Research Association, SF City inspectors (pg 7-8) estimated that 40% of existing illegal units have ceiling heights lower than the required min height of 7'-6". Accordingly, the study's recommendation was to explore the public health/welfare benefit of the 7'-6" min height requirement, since it precluded the creation of numerous legal dwelling units.
In Honolulu, we often see this as well -- Clients want to convert a basement into a living space, but commonly lack the required min 7'-6" ceiling height. Many basements have only 7'-0".
The only part of the article that I strongly disagree with, is the portion that says, "Concerns that make legalization of illegal units difficult, such as fire-resistant construction, safe plumbing and electrical services (often behind finished walls in existing illegal units), present little problem with new units." Older homes in Honolulu are often single-wall and it is quite difficult and costly to retrofit them to provide the ASTM E119 one-hour fire wall (an approved fire-rated assembly) that is required under the new Inernational Residential Code, adopted in 2009.
It is not sufficient to add a layer of 5/8" type-X gyp bd to each side of a single wall (1" thick T&G boards). That is NOT a tested, approved assembly that complies with ASTM E-119 and therefore not sufficient to provide the one-hour fire rated wall between dwelling units in a two-family dwelling. Although Table 721.2.1.4(2) of the 2003 and 2006 International Building Code (IBC) lists 5/8" type X gypsum wallboard as providing 40 min on protection, Honolulu Dept of Planning & Permitting has (in my experience) not accepted even 2-layers of type X on each side, as an approved alternate to an ASTM E-119 approved detail, shown at right.
Therefore, upgrading our older Hawaii-style homes to comply with the min requirements of the building code would require adding an interior "double wall" or 2x4 stud wall that extends up to the roof sheathing. And it raises other issues: if the existing single wall is load-bearing, should it be attached to the new stud wall? Or should a new stud wall be added to each side of the existing load-bearing single wall?Similar complications arise when an owner wants to create separate units: upstairs-dnstairs, as the floor-ceiling assembly must also therefore comply with a ASTM E-119 tested fire-rated assembly, that requires most older Honolulu homes to do costly retrofits.
Historically, that is to say prior to the adoption of the 2003 IBC an IRC Building Codes in 2009, Honolulu building codes did not require any fire-separation between two-family dwelling units (R-3 occupancy).
Since the ADU's are by LUO definition an "accessory use," (meaning the ADU is operated and maintained substantially for the benefit or convenience of the owners of the principal residence vs. a use that is separate from and unrelated to the principal use), ADU's should be exempt from the ASTM E-119 fire wall requirement if 5/8" type x gyp bd and smoke detectors are provided instead.
It is also important to keep in mind that if restrictions are too stringent, many homeowners will choose instead to simply build "Recreation Rooms" and convert those into illegal rentals. Remember that a Recreation Room does not require egress windows, a smoke detector, no fire-rated separation required between itself and the main residence's living area.Illegal Rentals therefore constitute the highest danger to its occupants, however, they are growing in popularity because of its simplicity.
As a community, we should therefore work to make it easier, to encourage adoption of ADU's.
