Exterior wall rating for detached structure

[Tsss]

2024 IRC

I am reviewing design for a partially built sauna, framing is up. It is located adjacent to an existing detached garage whose exterior wall is 5' to the property line, it is not attached to the dwelling unit. The new sauna is between the garage and the property line, with 0' separation to the property line. It was originally planned as an accessory detached structure, under 200 SF, and exempt from permitting per R105.2. The sauna is less than 200 SF but I am wondering if it being built against the existing garage (they share a wall) actually classifies it as being larger than 200 SF? The main question is whether or not the exterior wall on the property line needs to be rated 1-hour. R302.1 Exception 3 does not require a rating for sheds, playhouses, and similar structures exempt from a permit; but I am wondering if that will apply in this situation. Please let me know what folks think.

 

[Yankee Chronicler]

If the sauna shares a wall with the garage (in other words, the construction of the sauna involves building only three new walls) it is an addition to the garage and the areas of the garage and the sauna have to be combined.

Aside from that, the zero distance to the property line invokes a requirement for the exterior walls to be rated:



The exception doesn't mention saunas, and the 2021 IRC Commentary doesn't offer much additional clarity is to what might be considered "similar" in use to a tool shed or a playhouse. My inclination would be that a sauna is a more highly finished structure than a shed or a playhouse, and more intnded for human occupancy, so I would probably not allow it under this exception. But ... I'm not the AHJ.

R103.2 says accessory structures under 200 s.f. are exempt from permit ... but they are not exempt from complying with the code. So the requirement to rate the wall facing the property line is going to apply whether or not a permit is required.

Is there zoning in the jurisdiction where this project is located? Does zoning allow accessory structures with zero setback to property lines? That wouldn't be allowed in my home town.

 

[Tsss]

If the sauna shares a wall with the garage (in other words, the construction of the sauna involves building only three new walls) it is an addition to the garage and the areas of the garage and the sauna have to be combined.

Aside from that, the zero distance to the property line invokes a requirement for the exterior walls to be rated:

View attachment 17059

The exception doesn't mention saunas, and the 2021 IRC Commentary doesn't offer much additional clarity is to what might be considered "similar" in use to a tool shed or a playhouse. My inclination would be that a sauna is a more highly finished structure than a shed or a playhouse, and more intnded for human occupancy, so I would probably not allow it under this exception. But ... I'm not the AHJ.

R103.2 says accessory structures under 200 s.f. are exempt from permit ... but they are not exempt from complying with the code. So the requirement to rate the wall facing the property line is going to apply whether or not a permit is required.

Is there zoning in the jurisdiction where this project is located? Does zoning allow accessory structures with zero setback to property lines? That wouldn't be allowed in my home town.

The plan is to rate the wall on the property line since the sauna is contiguous with the garage.

Local zoning allows accessory structures to go to zero lot line at the rear portion of the lot.

R302.1 Exception 3 does provide an exception to the wall rating for exempt structures: "Detached tool sheds and storage sheds, playhouses and similar structures exempt from permits are not required to provide wall protection based on the location on the lot. Projections, external gutters, and storm drainage systems that extend beyond the exterior wall shall not extend over the lot line."

With regard to whether the sauna would fall under this use, it is typically only used for an hour at a time, which includes a lot of in and out; I would not consider it an occupied structure any more than a playhouse or tool shed that might be used as a workshop. But I am open to hearing otherwise.

 

[Yankee Chronicler]

What's the area of the sauna?

What's the area of the garage?

Does construction of the sauna involve building three new walls, or four new walls?

 

[bill1952]

Wouldn't all three walls of the sauna have to be rated, not just the one on the property line? And I'm guessing the garage wall is 5' so no rating required.

Just my opinion on the use, I think if it's insulated as I presume a sauna would be, it's habitable.

 

[Yankee Chronicler]

Wouldn't all three walls of the sauna have to be rated, not just the one on the property line? And I'm guessing the garage wall is 5' so no rating required.

Just my opinion on the use, I think if it's insulated as I presume a sauna would be, it's habitable.

Under both the IBC and the IRC, fire separation distance is measured perpendicular to the building walls. From the 2021 IRC Commentary:



I asked about the sizes of the building and the three or four walls because if (as the OP seems to have indicated) the sauna is not a free-standing building but an addition to the garage, then the total area is going to be over 200 square feet so the exemption from permits (and thus from requiring exterior wall fire protection) isn't applicable.

Personally, I don't think a sauna falls in the category of "Detached tool sheds and storage sheds, playhouses and similar structures" anyway, but I'm not the AHJ. But if the sauna is an addition to the garage, that debate is moot -- garages aren't exempt. That's why three walls or four walls is a pertinent question -- which has not been answered.

 

[Tsss]

What's the area of the sauna?

What's the area of the garage?

Does construction of the sauna involve building three new walls, or four new walls?

The sauna is 90 SF

The garage is 480 SF

The sauna has 3 new walls and an independent foundation and roof structure. A fourth sauna wall could easily be built flush with the garage, though rating the shared walls would be difficult.

 

[steveray]

R302.1 Exception 3 does provide an exception to the wall rating for exempt structures: "Detached tool sheds and storage sheds, playhouses and similar structures exempt from permits are not required to provide wall protection based on the location on the lot. Projections, external gutters, and storm drainage systems that extend beyond the exterior wall shall not extend over the lot line."

This does not apply if it is an addition to the garage...