Building Code - What Codes Apply

Codes vary depending on where you are located, but there is some commonality.

IRC building code

Most residential houses are covered under IRC code (International Residential Code) as long as they are less than 3 stories of living space above grade. Depending on the design, attics and basements may or may not be counted as stories.

Beyond that and you would enter the world of IBC (International Building Code) and those rules are generally considered harder to meet.

The height limit for IRC in seismic C, D, E, and F is 65 feet, although there may be some variation on how the height is measured when the land is sloped.

IRC has story height limits. It is 12 feet for masonry walls plus 16" floor thickness, ie 13'4" between the top of floors. These are just prescriptive requirements. It is ok to exceed these limits if the house is being structurally engineered.

The IRC code pulls together in one place most of the rules that you need to comply with in building your house. The final say on building codes rests with your local county so it is worth checking with them to find to what extent IRC is adopted for your area and any additional rules that have been added. Typically the variations from IRC are not likely to be more than about 10%, so following IRC is a good starting point. In my area, King County were very helpful in that they provided me with a photocopy of their enhanced version of the IRC.

Zoning rules

In addition to meeting the building code, you also need to comply with the zoning rules. These specify things such as how far your house needs to be from the property line or easement and how high the house can be. In my case, my house is a long way from the property line so I am only subject to the maximum allowed height which is 75 feet above grade. Zoning rules also specify the maximum percentage of plot area that can be impervious surface, but in my case with high acreage I am nowhere close to the allowed 15%.

Relevant building code

Some building codes (the prescriptive ones) are very clear, eg the height that a railing needs to be. Some are less clear (the performance ones) and to some extent it is up to the inspector to judge if you have met the intent of the code. When using more novel building materials and building techniques this works in your favor. If building your walls of concrete it's better to have a performance requirement regarding the strength of the walls than to have a prescriptive requirement that says you must make walls of 2x6 lumber. Sometimes you will be asked by the inspector to reference an official test report on the material you are using to prove that it meets the intent of the IRC. Hopefully such a report will be available from the manufacturer. In the case of the basalt rebar I import from China, I had to get it tested by an ASTM accredited test lab.

Sometimes you get to choose whether to abide by the prescriptive requirements or the performance requirements. If opting for the performance requirements then you typically have to have it designed by a licensed structural engineer. This is a negative but the trend these days seems to be for building departments to require proper structural engineering of houses in 95% of cases anyway, so you may as well go for the performance requirements.

With a concrete house that is properly engineered you are not going to have any problems meeting the wall (or floor if concrete floor) strength requirements or any of the live load or dead load requirements, but you do need to be careful with foundation design given that the house is extremely heavy. In my case I used a house weight estimate of 750 tons. That weight needs to be properly distributed into the soil under the house. The footings need to be wider than on a conventional house and it's good if the edge of the floor slab can help distribute some of the weight.

Often with unconventional construction it comes down to having a productive and professional conversation with your building inspector and your local building department. You need to argue your case and present your reasoning. Try to reference evidence that makes your case. Recognize that the building officials are there to help you build a house that is safe and does not have any structural or other problems. Listen to the advice you are being given as there is probably a reason for it. It is not in your interests to win the argument only to have your house fall down.