Wednesday, February 11, 2015

Tiny House Prototype that meets 2015 IRC Minimum Area Requirements

The shell for the 8'x16' prototype dwelling is near complete, and I'm now looking at interior layouts within the minimum requirements set by the 2015 International Residential Code (IRC). The structure is roughly twice the size of the units at Opportunity Village, and will include provisions for a small bathroom and kitchen. They will also be better insulated with rigid foam and an improved modular panelization technique that reduces air breaks.

Material costs to get the structure to this level of finish amounted to $4,025.73 (interior paneling not shown).
Note that this is still our prototyping phase and not necessarily exactly what the houses at Emerald will look like. 
With 2'x4' walls, the interior area comes out to 103 square feet, which just barely meets IRC under the following interpretation. Applicable code for interior area and height includes:

R304.1 Minimum area. 
Every dwelling unit shall have at least one habitable room that shall have not less than 120 square feet (11 m2) of gross floor area. ***Note: this requirement has been removed in the 2015 IRC thanks to a proposed changed change by Tom Meyer

R304.2 Other rooms. 
Other habitable rooms shall have a floor area of not less than 70 square feet (6.5 m2). Exception: Kitchens. 

R304.3 Minimum dimensions. 
Habitable rooms shall not be less than 7 feet (2134 mm) in any horizontal dimension. Exception: Kitchens. 

R304.4 Height effect on room area. 
Portions of a room with a sloping ceiling measuring less than 5 feet (1524 mm) or a furred ceiling measuring less than 7 feet (2134 mm) from the finished floor to the finished ceiling shall not be considered as contributing to the minimum required habitable area for that room.

R306.1 Toilet facilities. 
Every dwelling unit shall be provided with a water closet, lavatory, and a bathtub or shower. 

R307.1 Space required. 
Bathroom fixtures shall be spaced in accordance with Figure R307.1
- 30"x30" minimum shower size
- 21" clearance in front of toilet and sink (can overlap)
- 24" clearance for shower door
- 15" from center of toilet to side wall

R306.2 Kitchen. 
Each dwelling unit shall be provided with a kitchen area and every kitchen area shall be provided with a sink. 

I find no requirement that the sleeping area or kitchen must be in separate rooms, and instead could be combined in a "studio" arrangement.

So I believe it could be legitimately argued that a minimum legal area by 2015 IRC standards could be as small as one habitable room of 70 sq. ft. with sleeping area and kitchen, plus a bathroom as small as 18 sq. ft. while meeting minimum spacing requirements.

The sleeping area cannot be lofted legally since the loft will be a non-habitable space (due to area and height requirements for a habitable room). However the loft can still be added with an intended use for storage, and there are no access requirements in the code for non-habitable spaces. That point is verified here by one of the authors of the IRC:

"If you are ever challenged on the use of a ladder for non-habitable loft, be assured that the code allows it by default. Intentionally, there are no requirements for non-habitable loft access. I know this as I am the one that wrote this code section as it is currently provided for in the 2009 IRC. Fresh from the horse's mouth...not its posterior."

The above layout includes a 19.5 sq. ft. bathroom designed around a 32'x32' shower with 24" clearance in front of opening. And a toilet with 24" depth and 21" clearance (required clearance for bathroom fixtures can overlap). The only thing it fails to include is a sink with 21" clearance, but I couldn't bring myself to include that since there is a sink just a couple feet away. But I can foresee the issue being raised that sanitation and cooking are two separate water uses and require two sinks. If this has to be the case, a very small sink (such as this) could fit along the back wall if necessary.

The bathroom and living space are divided by a bifold door with a loft overhead. This room just barely meets the 70 sq. ft. at 7 ft. wide requirement (the bump out does not count as habitable space since it is less than 7 ft. wide.) The kitchen counter with sink is located on the same wall as the shower to cluster plumbing fixtures. The bed could be replaced by a futon for added function.

Overall this layout illustrates a minimalist approach to accommodating the minimum area and functions of a dwelling as defined by the 2015 IRC. I often hear people voice the need to change the building code, but its important to note that it has indeed been changing for the better (of tiny house builders) in the last few years, and it really is not that restricting. 

Municipalities often include area requirements above and beyond that, and those need to be challenged. Why exactly does our locale need standards above and beyond the national standard? And what exactly is that protecting? Given that the intent of the building code is to protect the health, safety, and well-being of occupants—and not surrounding property values—these questions are difficult to answer.

Moving the prototype from the shop to Opportunity Village.
Finishing out the exterior on site.


You can donate to Opportunity Village Eugene, the 501(c)3 non-profit developing the Emerald Village tiny house community, here:


  1. What was your anchoring for the structure?

  2. This is a step in the right direction. However, this is not an opportunity for people like myself who are seeking to either build a tiny house to their own specifications or buy one from say Small Home Oregon or Tumbleweed. In Eugene, there isn't a place to move a tiny house to. Eugene needs to develop a park that has the option to hook up to sewer, water and electric that you can take your tiny house to... much like Portland's Simply Home Living

  3. These were the relevant sizes from ICR 2015. Can you tell me what about the 2016. Are these sizes still same or changed? As a profession I am a roofer in Maryland that's why I want to know.

    1. The next scheduled revision to the IRC is in 2018.

  4. Great the structure is roughly twice the size of the units and will include provisions for a small bathroom and kitchen. They will also be better insulated with rigid foam and an improved modular panelization technique that reduces air breaks.
    dmv construction :)

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