Tiny House Building Code Compliance Part 2

This post is intended to explore the requirements for tiny houses that are placed on foundations on the ground (not placed on a trailer with wheels). These are likely to meet the dwelling criteria used by the International Residential Code and subject to permit requirements.

If you haven't already, I suggest reading the first installment of this series before heading into this "advanced" discussion.

As I stated in the first post, the International Residential Code (IRC) requires a number of minimum criteria for "dwelling units". The first is a requirement for at least one minimum habitable room that is 120sf in "gross floor area". Lacking a definition for "gross floor area" in the IRC, the user is directed to "other publications of the International Code Council". Chapter 10 of the International Building Code establishes "gross floor area" as "the floor area within the inside perimeter of the exterior walls of the building...".

If your tiny house house uses thick walls such as the cob house shown in the photo, you will not be given credit toward the 120sf for the wall thickness. Your building footprint will have to be expanded to include the room area in addition to the area comprised of the wall thickness. The 7 foot minimum habitable room dimension required by IRC Section R304.3 will also be measured from interior face of wall to opposite interior face of wall.

Once the code minimum area and dimension requirements for the this room are satisfied, the remainding code hurdles are initiated based upon what is provided within the dwelling.

Additional "habitable rooms" must have a minimum area of 70sf with the 7 foot minimum dimension and provided with a minimum ceiling of 7 feet in height. This can work to your advantage. The typical tiny houses I see on the net use a sleeping loft configuration that is pretty compact.

In order to be a habitable room, one must have the minimum 70sf room area. Frequently these spaces are designed to less than the minimum. As such, they are not "habitable" by the code definition. This allows the use of a ladder or other non-compliant vertical egress method to be employed for access since the IRC's stair and ramp provisions only apply to access to habitable spaces.

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.

Assuming that the minimum habitable room area is provided within the loft, the next test of habitability is ceiling headroom. The IRC requires 7 feet vertical clearance except when the ceiling is sloped. When the ceiling is sloped, only one half of the required room area must be provided with the 7 foot headroom clearance. If the room is required to be 70sf in area, then 35sf of the room must have 7 feet of clearance. Additionally, all the remaining required area must have a minimum of 5 feet of clearance. If this isn't provided, the room or loft cannot be deemed habitable.

This takes us back to the definition for "dwelling unit". In order to be considered a "dwelling unit", permanent provisions for living, sleeping, eating, cooking and sanitation must be provided. If you are asserting that your tiny house is a dwelling, the code official is unlikely to allow you to use your non-habitable loft for compliance with permanent provision for sleeping. Best to figure out a way to put a bed (fold out or otherwise) on the lower level. If you insist upon calling your loft the sleeping area, you are sure to be forced to comply with the minimum habitability requirements...including provision of those large and space consuming code-compliant stairs.

Kitchens are deeded habitable, but are exempt from the minimum room area. Earlier editions of the code required 50sf for this location. The current exception was also one of my code changes. If was quite a battle to get the ICC membership to delete this requirement. However, we prevailed. Based on this experience, it may be quite difficult to delete the 120sf and 70sf minimums in future codes. However, I think that a proposal to do so is certainly worth consideration for the 2015 edition.

Bathrooms are not deemed habitable, but still have some minimum clearances. "Bathrooms" and "toilet rooms" must have the 7 foot minimum ceiling height. Minimum area and dimensions are not stipulated aside from plumbing fixture "usability" clearances.

Toilets must have 15" of side clearance measured from either side to the centerline of the fixture. Toilets, lavatories, bathtubs and showers must have 21" clearance in front for access to the fixture. Showers must be provided with a minimum 30" by 30" shower pan. The room configuration must be such to allow for the fixture clearances. Doors may swing into any of the clearances. This is not clearly stated in the code, but it is the intent.

Hopefully this discussion is beneficial if you are trying to justify your minimum dwelling. This discussion applies only to the building code. Always be aware that zoning regulations or restrictive covenants may preclude the construction of these minimalist structures.

Photos of the cob buildings used by permission by Ziggy Liloia. His "Year of Mud" blog is an interesting and informative read if you are interested in owner built, minimal cob structures. Sustainable construction in its purest form.

Tiny House Code Compliance - 120 square feet exemption?

Recently I have been researching some alternative temporary housing for our land in Hotchkiss. I have somewhat intrigued by the so-called Tiny House movement. The proponents advocate living in little houses that are frequently less than 120sf in area. These houses provide full accommodation for living, sleeping, eating, and sanitation within a compact package. Many are constructed on dual axle flat bed trailers to permit portability. Don't like your neighbors? Hitch up and leave.

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There is lot of information on these buildings on the web. Interspersed is a lot of BAD information about code compliance methodologies. This blog is intended to set the record straight.

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The first question is determining if the building code is applicable to the structure or not. It is my opinion that any tiny house built and left on a trailer that is provided with tires and a license plate is not subject to building code oversight. If you are in Colorado, the legal precedent affirming this is Eason v. Town of Erie.

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Trailers constitute the building code dead zone that caused HUD to establish requirements for these factory built "mobile homes" years ago. The feds determined that nobody was paying any attention to these type of structures and decided that rules needed to be made. The old "mobile homes" burned hard and fast. Something needed to be done. I am not sure how the HUD regulations affect owner built "tiny houses" and don't proclaim to be an expert. This is one regulatory agency I try to avoid due to their notorious record for convoluted regulations and interpretations. However, I do believe that the "mobile home" must be at least 40' in length and 320sf in area to fall under their jurisdiction.

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If the house is sited on the ground (no trailer), then the building code comes into play. The International Residential Code regulates one and two family dwellings and their accessory structures. Many proponents cite the permit exclusion provisions for "sheds" that are less than 200sf (120 sf in the 2006 edition) in area. This is not a valid permit exclusion for the typical tiny house.

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The key here is the word "shed". The code states, "One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses...". It is hard to argue that these are mere tool sheds or playhouses when they meet the entire definition of Dwelling and Dwelling Unit contained in the code.

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2009 International Residential Code (IRC) Definitions:

DWELLING. Any building that contains one or two dwelling units used, intended, or designed to be built, used, rented, leased, let or hired out to be occupied, or that are occupied for living purposes.

DWELLING UNIT. A single unit providing complete independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking and sanitation.

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One could easily argue that a lack of one of the "permanent provisions" would preclude meeting the definition of "dwelling unit". Substitution of the built-in permanent stove with a plug-in counter top microwave would be one example. Elimination of the bathroom facilities is another.

If it isn't a complete "dwelling unit", then what is it? One could then argue it is a nice playhouse...exempt from building code permit requirements.

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Assuming that all permanent provisions are in place and the local code official makes the determination that the building is a "dwelling unit", the fun begins.

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The IRC prescribes some minimum areas for the dwelling. At least one room must be 120sf in area. All other habitable rooms except the kitchen must be 70sf in area. Minimum room width must be 7'. Minimum ceiling headroom must be 7'-0". The list goes on...and as you can see, so will your tiny house... going on down the road to some locale with no building code. Traditional tiny houses simply cannot comply with the IRC if they are determined to be dwelling units.

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A respondent stated the she thought that it would be possible to make the 120sf minimum area work. That may be possible. I will pick this idea up and explore it in a Part 2 post as a follow up to this discussion.

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Some will wonder why the code has so many restrictive requirements. These provisions go back beyond any memory, probably having their roots in the "tenement codes" first promulgated in places like New York City in the mid-nineteenth century. The intent was to provide for minimum habitability standards for conventional houses. Slum lord provisions, if you will.

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Truth be known, it is unlikely that any studies or analysis was conducted to ascertain that a building is safer or more habitable simply by having a single room with 120sf in area. Unfortunately, those that came up with these standards are no longer around to justify their existence. Old "tried and proven" code lore becomes absolute when the original basis for its inclusion is lost.

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Here is the moral of the story: Always do your homework first. Know the rules before you build or purchase. Understand the loopholes provided by the code and local case law. Query your code official on the requirements prior to bringing your building on the site. Be prepared to surmount some hurdles before enjoying your new-found minimalist venture.