Two adjacent lot line garages, one converted to living space, 1 hour both sides?

[iOne]

This is a tale of two adjacent lots with long driveways. On one side is a 1920's garage, and about 3 inches away the wall of a 1980's era "art studio" built with permits on a new foundation.

The shared wall space is 10'x20'.
Jurisdiction is in California.

Now the art studio is proposed for an ADU. I was expecting the building official to require the art studio wall to be upgraded to a 1-hour listed assembly -- which is plenty hard right there on a finished building. But they're requiring a 1 hour separation on each side of the property line. And that's a new one.

Both buildings have wood slat siding, the 1920's half is true dimensional lumber with no finish inside.

Is there a code basis for such a requirement? What if the neighbors, um, don't want to?

 

[Yankee Chronicler]

As a non-Californian, my view is that this is a case for the courts to decide. I can't see anything in code or in common law that allows a property owner to do something on his property that would require a neighbor to change anything.

 

[classicT]

Conventionally, the BO should only be able to make requirements for the building that the permit concerns. The other building, on separate property, would be allowed to remain as is.

 

[Inspector Gadget]

I concur with the above; the only time I consider what is on the other side of a property line when doing spatial separation calculations is if the other side of that property line is
a street, road, right-of-way or railroad track
a lake
a tidal water body

I explain it this way: I see an opaque grey wall at the property line. What is/is not may/may not be there is none of my concern.

I often hear "well, there's nothing there but forest."

"Yep. Now. How would you feel if I said "nope, y'all can't build there because your neighbour built something first?"

Most people get it at that point.

 

[ICE]

which is plenty hard right there on a finished building

I am curious as to what the plan is with the ADU 1hr. wall.

A similar problem arises when converting attached garages to a ADU. The wall between the ADU and primary dwelling is almost always shown on the plans as a 1hr. STC50 wall. The rub is that sometimes there's a kitchen or bathroom on the primary dwelling side of the wall. So how do you create a 1hr. STC50 wall with those conditions? The solution has been a false wall on the ADU side. I have never seen that on a set of plans but I have approved it many times. In fact, it is one of the questions I have at the first inspection.

 

[iOne]

I am curious as to what the plan is with the ADU 1hr. wall.
....The solution has been a false wall on the ADU side. I have never seen that on a set of plans but I have approved it many times.

Approved it in what capacity?

On my side in some cases we've permitted as a Junior ADU (JADU) to sidestep the internal wall fire separation requirement. But that involves a deed restriction for owner occupancy that most people don't want to sign, and is super dangerous in a Rent Control jurisdiction.

In some cases I've used the Component Additive Method, to prove out the common wall maybe w/some rockwool added.

In some cases I've said nothing and it just slides, on the notion that the kitchen side was "not part of the scope of work". So the AHJ accepted a one sided one hour wall.

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What I'd like to do is an AMMR -- Alternative Materials and Methods -- to treat the combination ADU + House as a single fire zone, and require cross connected detectors. There's no evidence that upgrading existing interior walls in divided home will actually resist fire for an hour: there are just too many ways for fire to spread. It's better to get everybody out as if it were a single occupancy.

But so far no AHJ has accepted that type of AMMR.

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You could try some Intumescent paint on the kitchen side. But that's clearly studying to the test, rather than the actual exercise of creating a safer home.

What have you done?

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Building a false wall does NOT necessarily meet the 1 hour separation.
If the kitchen side is non-rated, a sharp eyed plan checker will give it a 0 hour rating.
Then the false wall has to be structural, assuming the entire kitchen side wall burns to a crisp.

 

[Joe.B]

Neither the BO, the applicant, nor the courts could impose a required change to the neighbor's property. I think the code is pretty clear on the requirements. If it's a CRC design, then table R302.1(1) tells you that your exterior wall that has a fire separation distance of less that 5 feet shall be "1 hour—tested in accordance with ASTM E119, UL 263 or Section 703.3 of the California Building Code with exposure from both sides. If for some odd reason it was a CBC design then 705 would produce the same result, albeit in a much more thorough way.

If you end up in 722 to get your rating, then you'd need to consider:

722.6.1.2 Dissimilar Membranes
Where dissimilar membranes are used on a wall assembly that requires consideration of fire exposure from both sides, the calculation shall be made from the least fire-resistant (weaker) side.

 

[ICE]

Approved it in what capacity?

Tiger.

 

[ICE]

In some cases I've said nothing and it just slides, on the notion that the kitchen side was "not part of the scope of work". So the AHJ accepted a one sided one hour wall.

That is common. Usually when the job has progressed to the point that the customer says. "Well it's too late now. You had your chance and blew it. Are you going to fail the final inspection?"

Yes, yes I am. However, you have the option of a "Sorry I missed you" correction notice. Then you hope for the original inspector to show up and pass the final inspection.

 

[steveray]

art studio to ADU both sound like IRC structures so no change of use so no upgrade....Shirley I could push it either way in the IEBC, but let's start there...

 

[classicT]

art studio to ADU both sound like IRC structures so no change of use so no upgrade....Shirley I could push it either way in the IEBC, but let's start there...

How do you figure? In what way is an art studio a dwelling unit?

Sure, if built as a detached accessory structure to a residence, it can be built per the IRC... but to say there is no change of use, I strongly disagree with. Even under the IRC, a change of occupancy is defined such that a change in the application of the requirements of the code is a change of occupancy. ADU have very specific requirements for fire separation, alarms, etc. that would not apply to a residential accessory building.

2021 IRC
[RB] CHANGE OF OCCUPANCY. A change in the use of a building or portion of a building that involves a change in the application of the requirements of this code.

 

[steveray]

How do you figure? In what way is an art studio a dwelling unit?

Sure, if built as a detached accessory structure to a residence, it can be built per the IRC... but to say there is no change of use, I strongly disagree with. Even under the IRC, a change of occupancy is defined such that a change in the application of the requirements of the code is a change of occupancy. ADU have very specific requirements for fire separation, alarms, etc. that would not apply to a residential accessory building.

2021 IRC
[RB] CHANGE OF OCCUPANCY. A change in the use of a building or portion of a building that involves a change in the application of the requirements of this code.

R101.2 Scope​

The provisions of this code shall apply to the construction, alteration, movement, enlargement, replacement, repair, equipment, use and occupancy, location, removal and demolition of detached one- and two-family dwellings and townhouses not more than three stories above grade plane in height with a separate means of egress and their accessory structures not more than three stories above grade plane in height.

There is not a different requirement for dwellings to property lines than accessory structures in R302....Correct?

R302.1 Exterior Walls​

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 Section P2904 shall comply with Table R302.1(2).

 

[classicT]

There is not a different requirement for dwellings to property lines than accessory structures in R302....Correct?

No, there is not a different requirement as it relates to FSD.

But it is still a change of occupancy, which is where depart from your assertion.

 

[steveray]

No, there is not a different requirement as it relates to FSD.

But it is still a change of occupancy, which is where depart from your assertion.

I spoke a little flippantly...I do that here....But you agree there is nothing in the IRC that would require the exterior wall to be upgraded?...As I cleverly get us back OT.....Of course the OP put this under the IFC, so maybe all of this is moot....?

WHEW...got my sawhorse back...was starting to get the shakes....

 

[classicT]

No, because it is a change of use and ostensibly to a higher risk, I would require the wall to be brought up to code.

 

[Yankee Chronicler]

That is common. Usually when the job has progressed to the point that the customer says. "Well it's too late now. You had your chance and blew it. Are you going to fail the final inspection?"

Yes, yes I am. However, you have the option of a "Sorry I missed you" correction notice. Then you hope for the original inspector to show up and pass the final inspection.

Our plan review letters and our permits both include a statement that our failure to cite an issue at plan review and our issuance of a permit does not authorize any violations of codes, and any issues noted during inspections must be corrected.

This upsets some people. When I was starting out as an architect in the 1960s and 1970s, this concept wasn't as well established in law. I actually met some architects at AIA functions who were proud of the fact that they were able to get AHJs to "approve" non-compliant features in their designs by intentionally including obvious errors in the first set of construction documents. Their ploy was to hope the plan reviewer would cite the low-hanging fruit and not find the things the designers really wanted, but which didn't comply with the code. We're not playing that game.

It was a reprehensible and unprofessional attitude then, and it's no more so today. The difference is that, back then, there were people doing it intentionally. Today, I think the level of code knowledge on the part of architects -- in general -- has dropped so far that now they have no idea what the codes require. I try to provide an explanation and a code citation for every comment in my plan reviews. Often they still don't get it. (My boss shakes his head over some of the resubmittals, that still get things wrong -- "You wrote them an encyclopedia!") Either they don't own a code book, or they're functionally illiterate.

 

[steveray]

No, because it is a change of use and ostensibly to a higher risk, I would require the wall to be brought up to code.

There are no "risks" in the IRC......funny that in two similar topics we kind of switch positions...

 

[iOne]

Table R302.1(1) tells you that your exterior wall that has a fire separation distance of less that 5 feet shall be "1 hour—tested in accordance with ASTM E119, UL 263 or Section 703.3 of the California Building Code with exposure from both sides.

If I have to get the neighbor's permission to demolish and rebuild their garage, getting to 1 hour rating is easy. Without that, it's really.... remarkably hard....

Both the component additive method and the UL listing system methods assume walls built
from both sides. Testing is so expensive, many fully effective wall construction methods will never be tested because there's nobody who would profit enough to pay for the testing.

UL U415 UL System (3.125 in. thick STC 34) might work:


Except then the existing wall is outside the fire envelope, and the roof has to be supported with new posts or columns. Messy.

All this for a 150 square foot building that can be evacuated in seconds with no interior doors, stairs or anything.

 

[iOne]

From the OP: the actual buildings.

Both were built with permits in their respective eras - 2002 and 1020. The left is the art studio/garage with room for 1 car, but never actually used to store a vehicle of course because hardly anyone 'round these parts bothers to garage a car.

 

[Joe.B]

If I have to get the neighbor's permission to demolish and rebuild their garage, getting to 1 hour rating is easy. Without that, it's really.... remarkably hard....

All this for a 150 square foot building that can be evacuated in seconds with no interior doors, stairs or anything.

You're absolutely correct. Probably easier to knock down the "art studio" and start fresh. Even easier to let good enough alone and leave it as is.

But if you want more housing then do it right. Sure, it's only a 150 sq. ft. building, but it adds value to the property and whoever inherits it or buys it later is going to assume it was done correctly. If you can't tear it down and start fresh, and can't get the wall rated from the outside, then you need to hire someone with a stamp and have them design an equivalent assembly. Preferably someone who can present it to he AHJ in an easily digestible manner and present how it meets equivalent safety. For example, maybe they would allow you to install a fire sprinkler system in-leu of a fully rated assembly? I don't know but that sounds reasonable to me...

 

[steveray]

If I have to get the neighbor's permission to demolish and rebuild their garage, getting to 1 hour rating is easy. Without that, it's really.... remarkably hard....

Both the component additive method and the UL listing system methods assume walls built
from both sides. Testing is so expensive, many fully effective wall construction methods will never be tested because there's nobody who would profit enough to pay for the testing.

UL U415 UL System (3.125 in. thick STC 34) might work:

View attachment 12847
Except then the existing wall is outside the fire envelope, and the roof has to be supported with new posts or columns. Messy.

All this for a 150 square foot building that can be evacuated in seconds with no interior doors, stairs or anything.

Let the building department spell out the code path to the "required" upgrades...They won't be able to......

 

[Joe.B]

Let the building department spell out the code path to the "required" upgrades...They won't be able to......

Hahaha, is that a challenge?

 

[steveray]

Hahaha, is that a challenge?

Not outright...I just don't think it exists......

 

[classicT]

Let the building department spell out the code path to the "required" upgrades...They won't be able to......

It's not their responsibility to do such... Contractor and design professional should have a better idea though.

The building department only needs to perform the plan review and inspection. If something is rebuilt, it needs to conform to the IEBC. If the IEBC requires it to be upgraded, it is up to the design professional and contractor to do such. Only if they fail to do so does it become incumbent upon the local building department to identify.