# Existing Home Garage Conversion to ADU



## PC_Number

Problem: 
Existing 2 story home would like to convert the existing 1st floor Garage to ADU. Code section R302.3 requires a 1-hr floor assembly between the two dwelling units, and 1-hr rating at the supporting construction. What have you seen as design solutions. People will not want to reconstructed the floor assembly to create the 1-Hr rated assembly. 
One possible solution is shown in the link below:
https://www.portlandoregon.gov/bds/appeals/index.cfm?action=getfile&appeal_id=14189&file_id=14773  

I am looking for a tested listed and approved retrofit 1-hr fire rated floor assembly or any creative solutions. 
Any help or insight would be greatly appreciated.


----------



## ADAguy

Doing this as: owner, AOR, contractor or other?
Who people, don't want to?


----------



## cda

Welcome 

There are other Calif’s on the site


----------



## cda

IEBC enforced??


----------



## cda

http://www.hcd.ca.gov/policy-research/docs/FAQsADUs.pdf


----------



## ADAguy

Good background but doesn't address his question.


----------



## PC_Number

I am a plans examiner. Just wondering what other jurisdictions have approved in the past. The problem is creating a 1-Hr fire separation at the ADU and Main Dwelling units between the 1st and 2nd floor without having to redo the second floor framing to create a listed 1-hr rated floor and ceiling assembly.


----------



## cda

PC_Number said:


> I am a plans examiner. Just wondering what other jurisdictions have approved in the past. The problem is creating a 1-Hr fire separation at the ADU and Main Dwelling units between the 1st and 2nd floor without having to redo the second floor framing to create a listed 1-hr rated floor and ceiling assembly.




Not into design, but how about something like shaftliner?

https://cache1.buildgp.com/wp-conte...aftwell-stairwell-systems-technical-guide.pdf


Does your city have any written guidance on ADU,,

or just use base code?


----------



## mark handler

In CA
Accessory Dwelling Unit Memorandum December 2018
http://www.hcd.ca.gov/policy-research/docs/ADU-TA-Memorandum.pdf

http://www.hcd.ca.gov/policy-research/AccessoryDwellingUnits.shtml#booklet


----------



## ADAguy

How about if you add sprinklers?


----------



## Pcinspector1

Good info Mark!


----------



## Pcinspector1

I assume you've looked at the GA-600-2015 for gyp systems?


----------



## PC_Number

Good Idea with the Shaft Liner I was thinking along the same lines but shaft liners are for "walls". I have looked into the gypsum association listed assemblies. Again, they have a lot of approved wall assemblies but not much for floor rated assemblies.


----------



## cda

PC_Number said:


> Good Idea with the Shaft Liner I was thinking along the same lines but shaft liners are for "walls". I have looked into the gypsum association listed assemblies. Again, they have a lot of approved wall assemblies but not much for floor rated assemblies.




Not into all that design stuff,

But does the code just require one hour seperatation ??


Base code not calif 

*R302.3 Two-family dwellings.*
Dwelling units in two-family dwellings shall be separated from each other by wall and floor assemblies having not less than a 1-hour fire-resistance rating where tested in accordance with ASTM E 119 or UL 263. Fire-resistance-rated floor/ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend from the foundation to the underside of the roof sheathing.


----------



## mtlogcabin

What do you have for floor joist? Dimensional lumber or I-Joist?
16" or 24" OC spacing


----------



## PC_Number

We have dimensional lumber.
CDA: Look at section R302.3.1 Supporting Construction.
This requires elements that support the 1-Hr Fire Rated Assembly to get the 1-hour rating too.


----------



## Pcinspector1

Support beam and post will need to be protected that supports the floor above. Do you have access to a gypsum catalog for a 1-hr protection design?


----------



## mark handler

ADAguy said:


> How about if you add sprinklers?


State says they are not required unless the main house has them


----------



## mtlogcabin

If the joist are 16" OC then you can use IBC chapter 7 other wise it is not hard to find one hour floor ceiling assemblies
Remember the fireside is the ceiling and 2 layers of type X or C is all most assemblies use
The fireside for supporting construction in the conversion of the garage is the interior side so again it will be a simple single or double layer to achieve this  unless CA have amended the IRC


----------



## ADAguy

mark handler said:


> State says they are not required unless the main house has them


Not required but can't they be used in lieu of 1 hr?


----------



## mark handler

ADAguy said:


> Not required but can't they be used in lieu of 1 hr?


what is need for 1-hour?
Unit seperation? IMPO, NO


----------



## steveray

If it is Accessory no, if it is Additional, yes....At least around here....And the entire garage would have to meet current energy code including floor/slab...That is what usually gets them here, but you do not have as harsh of a climate...Can you use 721 IBC or whatever the archaic assemblies section is?


----------



## mark handler

steveray said:


> If it is Accessory no, if it is Additional, yes....At least around here....And the entire garage would have to meet current energy code including floor/slab...That is what usually gets them here, but you do not have as harsh of a climate...Can you use 721 IBC or whatever the archaic assemblies section is?


Here too, but unless it is attached, or close to a Property line, no need for one-hour


----------



## mtlogcabin

steveray said:


> And the entire garage would have to meet current energy code including floor/slab...



Not everywhere

2012 IECC
Slab-edge insulation is not required in jurisdictions designated by the code official as having a very heavy termite infestation.


----------



## Robert

mtlogcabin said:


> If the joist are 16" OC then you can use IBC chapter 7 other wise it is not hard to find one hour floor ceiling assemblies
> Remember the fireside is the ceiling and 2 layers of type X or C is all most assemblies use
> The fireside for supporting construction in the conversion of the garage is the interior side so again it will be a simple single or double layer to achieve this  unless CA have amended the IRC



If the fireside is ceiling only, why do many floor/clg. assemblies require a double wood floor or concrete topping? Would that be for acoustic control?


----------



## cda

Robert said:


> If the fireside is ceiling only, why do many floor/clg. assemblies require a double wood floor or concrete topping? Would that be for acoustic control?




My take,,
Sometimes part of the fire rated tested assembly


----------



## mtlogcabin

I-Joist 24" OC
https://awc.org/pdf/codes-standards/publications/dca/AWC-DCA3-FireRatedFloorWall-1007.pdf

Note 1 the floor topping is optional in the assembly not required


----------



## classicT

UpgradeCabinets said:


> ADU? Whats this mean?


Accessory Dwelling Unit - an apartment unit


----------



## ADAguy

Poster is from Daly City, CA; what say you to CBC requirements Mark,.
is this a local AHJ call?


----------



## PC_Number

I know that some jurisdictions review it as Two Family Dwelling Units. Because there are 2 families living there. Requiring 1 hour fire rated assembly separation and Noise attenuation. But according to this thread it is not needed in some jurisdictions. So yes it would be the call of the AHJ. This applies more to CA because of the “housing crisis” and recent legislation.


----------



## mark handler

3G A-600-2009 FIRE RESISTANCE DESIGN MANUAL
The Hard Part will not be the fire rating, which is required but you will need a 50 STC and ICC rating


----------



## mark handler

ADAguy said:


> Poster is from Daly City, CA; what say you to CBC requirements Mark,.
> is this a local AHJ call?


*California Department of Housing and Community Development *
Accessory Dwelling Units (ADUs)
*Accessory Dwelling Unit Memorandum*
http://www.hcd.ca.gov/policy-research/docs/ADU-TA-Memorandum.pdf
*General info and New Laws*
http://www.hcd.ca.gov/policy-research/AccessoryDwellingUnits.shtml


----------



## ADAguy

Good stuff, thank you


----------



## J2architect

PC_Number said:


> Problem:
> Existing 2 story home would like to convert the existing 1st floor Garage to ADU. Code section R302.3 requires a 1-hr floor assembly between the two dwelling units, and 1-hr rating at the supporting construction. What have you seen as design solutions. People will not want to reconstructed the floor assembly to create the 1-Hr rated assembly.
> One possible solution is shown in the link below:
> https://www.portlandoregon.gov/bds/appeals/index.cfm?action=getfile&appeal_id=14189&file_id=14773
> 
> I am looking for a tested listed and approved retrofit 1-hr fire rated floor assembly or any creative solutions.
> Any help or insight would be greatly appreciated.



Did you find a creative solution? I have an exact condition and I have no issues finding a 1 hour rating assembly the hard part is meeting the stc 50 requirement.


----------

