Saturday, November 13, 2010

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.


David Eisenberg said...

Thanks Tom, for providing such useful and clear information and explanations of the code in relation to small houses and habitable spaces. I have long thought that it would be a worthwhile endeavor to create a code for very small dwellings (dwelling units) that provided the kind of flexibility that would encourage, instead of discourage, the building of very small houses. It is on the long list of things we would do at DCAT if we were fully funded and staffed... Maybe someday...or even better, maybe someone else...

Brian Payne said...

Unfortunatly, my code official didn't buy the argument and is not letting me permit a nonhabitable loft in my kid's bedroom. Any advise?

Tom Meyers said...


I can only tell you what the IRC says and what its intent is. I assure you that the code is only inclined to address normally occupied spaces and does not intend that the loft space be made habitable or that it be provided with R311 compliant stair or ramp access.

Often, houses are provided with "plant shelves" and other loft like projections used for a variety of decorative purposes.
The loft in a child's bedroom could be used for similar purposes.
I am not inclined toward discriminatory enforcement in my regulatory practice. Therefore, I apply the code literally: There is no stated prohibition against shelves or lofts. If a shelf or loft is provided, I determine if it is habitable or not. In order to be habitable, it must meet ALL of the criteria for area and headroom. If it is not habitable, I do not regulate access. If it is habitable, then I require access via a stair or ramp. I will also require light and ventilation and anything else the code attaches to habitable spaces...but ONLY when that space is deemed habitable.

Good luck with your project.


Andy said...

The more research I did about the actual building of a tiny house, the more I thought it was possible, even with my limited funds.

The more research I did on building codes, the more I FOUND OUT it's impossible.

I've pretty much given up on my dream of having a tiny house, discussing it is a waste of time.

I just write this out of bitterness and hatred of people who tell others what to do with their property.

Where I live they force you to build a house at minimum 1,100 heated square feet. That's insane, I don't need that much room and never will. I should be able to do what I want with my land as long as the house is safe.

But no, these SOB's want their tax revenue, you can go live in a GD apartment your whole life and pay someone else rent.

Anonymous said...


I read both your entries that Kent linked to from the THB. Great info! I bookmarked your blog and plan to read more of it. Keep up the good work!

Cheers, -anon

Mark Bailey, Archt. said...

David, Brian, Tom,
By chance is this space less than one-third of the area of the room or space in which it is located? IRC, See 'Mezzanine, Loft in R202 definitions.' 'intermediate level or levels between the floor and clg. of any story with an aggregate floor area of not more than one-third of the area of the room or space in which the level or levels are located.'I believe it becomes a 'habitable loft'. If that is allowed beyond the definition is subject to further review. I know of no further reference in the IRC to said 'loft or mezzanine' but Tom might.
IRC is very clear on 'Occupied Space' "total area of...on a horizontal plane...." could work in your behalf when that loft space is included in the space below (clearly defined in 505.1 of the IBC) yes, not residential but could be a related precedent and says the "space is to be included in determining the fire area as defined in 702". therefore; part of the overall area. 1992 CABO had no reference to mezzanine or loft and UBC defined Mezzanine as an 'intermediate floor placed within a room' and allowed them under Sec. 1716'Rooms may contain mezzanine floors'...(ancient history but may have gotten lost between 1988 and now...) The residential code appears to require further clarity on this loft or mezzanine as the intent here is to be within code and within reason, it is all about life safety. The 'intent of the code' is to not create a dangerous condition thru its interpretation.
A smoke detector is still required and even a domestic sprinkler head (run off the house 1/2" supply line) is allowed under the IBC (may affect here if interpreted by local authority allowing same) put your design 'well beyond' minimum code-compliance and create a far safer occupied space.
We are all on the same team here, ask your code official if he can think of an alternative that might help you comply with the code and get this built. see R1014.10 'Modifications'...details of any granting of an approval to a modification will go in the file, perhaps you as the Owner can write something to the effect that you will accept these allowances as non-compliant and do not foresee that they create a dangerous condition to life-safety (especially if you make means of going beyond the word and intent of the code). This can go in his file and absolves the authority having jurisdiction of its level of liability in regard to those issues. This guy is doing his job and interpreting that code...every day...
further thoughts...?
Mark Bailey, Archt.

Tom Meyers said...

As a follow up to your comment...I feel your pain. You are caught in an era of increasing regulations that often are there to benefit the lowest common denominator without permitting the use of logic and reason. That is the reality of our nanny state.
In fairness to the building code, it is NOT the reason you are forced to 1100sf minimum. Those are local planning and zoning requirements. Those type of things have NOTHING to do with life safety. They are about exclusion. Exclusion of "lesser" dwellings that are perceived to drive down adjacent property values. P&Z regs create pockets of like-minded individuals with like-minded pursuits. You need to find land in a place that has your interests at heart. Find an older neighborhood (prior to the 50's usually) that does not set minimum dwelling area. Build in the country. But be warned that NIMBY proclivities lurk in the cities, especially new portions.
With some research, you can find what you are looking for.

Tom Meyers said...

Mark and all:
I always like the suggestion of trying to work this out with the building official up front. I like to think that the majority of those in my profession understand that the prescriptive code has its limitations and that Sections R104.10 and R104.11 are available to assist in achieving an equivalent level of life safety.

In regards to mezzanines...the term is used in the IRC to establish that a mezzanine (meeting the IRC definition) is not considered a "story". This is used primarily to scope structural issues, particularly lateral bracing. Otherwise, its application is pretty limited (unlike the IBC where it has lots of benefits).
One may use it if there if having multiple stories is not beneficial. We find this in the 200sf tool and storage shed exception that limits the building to one story. One could have a mezzanine in this structure and still be "one story" in height.
The term "mezzanine" has no bearing on habitability. Either a location in the building is habitable or it isn't. To be habitable, it must have minimum height and area...and provided with an R311 means of egress.


arlos said...

As one who has been in construction the better part of 40 years, it is clear here a whole new code set must be developed for tiny homes.
I perfectly understand Andy's frustration. The tiny house is not a mini me nor is it a redhead bastard stepchild. It is an entirely stand alone habitat and must be addressed from that. There is nothing that will kill the dream faster than the building counter in any city.

Dom said...

Perhaps this seems lazy, but this kind of regulation baffles my mind. Never been that good at following rules. I'm trying here though. I want to build a small "shed" to keep some things in and "camp" in a couple months a year. (I live abroad mostly) The town population just increased to put it over the 2000 mark -which means I need to deal with building codes. I'm not going to have plumbing, only a couple solar shed lights, and no electrical wiring.

Any chance you could direct me to a link for that Shed code that applies. The land is in Maine and seems like there are no other local regulations to deal with.

Rudy Mc Landey said...

I went to my County Planners office and discussed the merits and hazards of my desire to build a Tiny House. Philosophically he embraces the concept of smallness as a greening strategy, but officially he is bound by existing code. I provided him with some links to Tiny House websites to further his sympathetic understanding of what we are trying to do.

In the meantime, we also discussed the code minimums for permanent dwelling. In my county the minimum is 150sf of heated floorspace for the first occupant, and 100sf extra per each additional occupant (not including bathroom). In the end, 250sf is not that big a burden to build. Cost wise, I can mill my own lumber from trees cut off the property, I can build with Cob but will need an engineer's report endorsing its safety ($$) will need a foundation inspection ($$), plumbing inspection ($$), Electrical inspection ($$) Septic Tank permit and inspection ($$), and a Certificate of Occupancy ($$) and I'm sure I've left something out. The cost is not the construction itself, but the Big Brother intrusion siphoning off my construction budget.

For now, I'm sticking with the trailer. I'm way out in the woods, adjacent to National Forest, out of sight, out of mind. When I have more money for something permanent, I'll probably do Cob with full timber rafters.

Thanks for what you are doing here.

Kirsten N. said...


Thanks so much for your post. I'm so pleased to know that someone with your insight is working on the IRC.

I'm in Ontario, dealing with the Canadian building code, which is similar but (of course!) a little different. We also ended up buying property in a rural area that we *thought* would have less restrictive codes, but turns out to have a 44 square metre minimum size requirement. (Fortunately that's only about 750 square feet).

Our eventual solution was to buy an old farmhouse with a good foundation. I can close off the upstairs and renovate the main floor to live in just under 500 square feet.

What our zoning by-law actually says is "The floor area for Seasonal Dwellings and Hunt Camps shall not less than 44 square metres." I did not win any points with the inspector by pointing out that it didn't mention year-round dwellings!


Kenise said...

Thanks for all the great info Tom. I live in the bay area in No.CA in an upwardly mobile area. I've wanted an ADU for years and discovered tiny living. My local zoning requires a max of 15' structure because they don't want any two storys. I plan on taking my chances and building in the backyard. I plan on using a gambrel roof to give more room in the 'loft'. Wish me luck

Tom Meyers said...

Regarding height restrictions and stories: Remember that most regulations measuring height work from the "grade" or "grade plane". This can be used to your advantage. If you place the lower level into the ground (think earth sheltering), you can reduce the overall height measured from one of the grade locations. Flat (low slope) roofs are also worth consideration for height and rainwater harvesting. Don't let the regulations dictate your building. Use the regs to foster creativity and efficiency you would have otherwise neglected.

london builders said...

I don't have much idea regarding this....but the tiny house in the pic is smart indeed.

Lee said...

I believe that the IBC codes are slightly more prohibitive than the IRC codes. Keep that in mind. Tom, do you see it this way? The IBC uses "net square feet" for criteria, while the IRC usus gross. Does "net sq. ft." not include cabinets?

Also, the IBC has "efficiency dwelling" rules. IBC 1204.8, I think. It's minimum is 220 net sq ft. for the liveable room. A separate closet is also required.

So, do tiny stand alone houses count as efficiency dwelling units? Does having a separate bedroom make a difference, if they are otherwise efficiency dwelling units?

Taichi said...

Does anyone know for efficiency design, do kitchen counter and cabinets considered part of the habitable space, i.e. included in the 120sf of living space?

Tom Meyers said...

Kitchens are not habitable space. So it would be my opinion that they would not be included in calculating the 120sf for the minimum habitable room. Read my most recent post. I am going to take a run at eliminating the 120sf minimum. Now that you raise this, I may include the efficiency unit also. I will probably have to first try a downgrade to 70sf. Tom