Attached Accessory Dwelling Unit Fire Separation

[Bay80]

I am looking to get a feel for how code officials are working with and regulating attached ADU's. These items have become the new hot topic in Massachusetts. I for one am all for them as I think it will help mitigate the lack of housing, but trying to build them safely seems to vary from town to town. I've worked in some towns where all you need to do is meet the setbacks and the sqft requirements and your good to build. I've worked in others where a fire separation on par with the fire separation required for a duplex was required. I wanted to get a feel from the folks on here as to how you have been working with these units as far as fire safety goes. Are you requiring a full fire separation, just a 15 min, does having a residential sprinkler system change the parameters your using? We are currently using the 2015 IRC with specialized MA amendments for a code reference.

Thank You all in advance for your input I'm eager to see the varying opinions with this question.

 

[steveray]

If it "becomes" a 2 family building, it gets a fire rating...if it is 2 buildings on the same lot in close proximity, it gets a fire rating....The devil is in the details....

Welcome to the forum!

 

[fatboy]

Attached single unit makes a duplex, follow the sections for duplexes........as steveray said, on the same lot, follow FSD sections .

 

[TheCommish]

ADU, sometimes called accessory apartments, also called in-law apartments are not new to Massachusetts or the town that I server. We have had allowances for attached accessory apartments by right (no additional zoning review) with size and living unit configuration, one a building permit has been issued since 1991. Duplexes have been allowed in certain zones since 1987, with the definition of independent living units.

Chapter 358 of the Act of 2020 made several amendments to Chapter 40A of the General Laws, commonly known as the Zoning Act. Provided a mechanism with a simple majority threshold rather than a super majority (2/3) vote allowing communities amend their local zoning to allow for attached and detached ADU.

Once we leave the zoning requirements, the building code definitions come into play. A duplex in Massachusetts each unit has 2 independent means of egress, with separation requirements. To be an accessory apartment the ADU must be part of and share one of the means of egress from the principal dwelling. The home with the ADU now has an additional bedroom, 2 kitchens and possibly an additional bathroom, with a non-rated wall between living units.

If my community was to allow detached ADUs, the building code separation distance for structures from property lines would come into play if the zoning setback did not govern. The setback for most zones in my community are 15 foot from lot lines.

Separation between the principle dwelling and the accessory dwelling is covered by R302.1 (2015 IRC) Construction, projections, openings and penetrations of exterior walls of dwellings and accessory buildings shall comply with Table R302.1(1); or dwellings equipped throughout with an automatic sprinkler system installed in accordance with NFPA 13D shall comply with Table R302.1(2). Exception 2 Walls of dwellings and accessory structures located on the same lot.

References

https://www.mma.org/wp-content/uploads/2021/03/GuidanceOnZoningActVotingThresholds_2.26.21.pdf

 

[Yankee Chronicler]

IMHO, unless and until the IRC explicitly addresses ADUs, there is likely to be a disconnect between local laws and zoning regulations that allow ADUs and the IRC on two-family dwelling units. A lot will depend on how the ADU regulations are crafted as to whether or not there are disconnects netween the ADU regulations and the IRC.