A building code is a set of rules that specify the minimum acceptable level of safety for your new home or room addition you plan on designing. The main purpose of the building code is to protect public health, safety and general welfare as they relate to the construction and occupancy of buildings and structures. The building code becomes law of a particular jurisdiction when formally enacted by the appropriate authority, such as the City Council. The most popularly used building code today is the International Residential Code or we just call it the IRC. Other building codes are the BOCA, the Southern Building Code or SBC and the Uniform Building Code or UBC.

Although the code book is as thick as the New York City telephone book, I am going to point out for you several top International Residential Codes that you need to watch out for in your home design process;

• First, this isn't actually a Building Code but you need to know what Building Code and what YEAR your Building Inspector will be referring to. Right now it is 2010 but the City of Dallas is referring to the 2006 Code Book. In most cases, cities adopt the latest code every 4 years. So I suppose in 2011 we will be referring to the 2010 code book. Call your city to find out for sure.
• Hallway clearance is 36 inches. This could include protrusions into the hallway such as stair parts and cabinets along the wall. So make sure you can take a yard stick and easily move it down the hallway at any elevation below the minimum head room.
• Minimum headroom is 80" or 6'-8". This is why doors are 6'-8". As my own rule of thumb, I always try to maintain a minimum headroom of 84" or 7'-0" below fur downs and in stairway vertical clearances. Often more on stairways to prevent that sensation of you're about to hit your head on the wall above.
• Emergency Egress for Habitable Rooms. Every "Habitable" room needs to have the require egress openings. By Habitable Room, they mean sleeping room or bedroom. I've seen some Building Inspectors get very strict on this meaning. If the room looks like it could be used as a Bedroom, then it's treated as a Bedroom. Code requires that all habitable rooms have two means of egress. Egress is just a fancy word for "getting out". The International Residential Code (IRC) Section R310 defines an emergency egress as an opening that's minimum 5.7 square feet*, minimum 24 inches vertical clearance, minimum 20" horizontal clearance, and a sill height no greater than 44" above the floor. *Ground floor windows can be 5.0 square feet.
• Stairs.... This changed a lot in the pass several years. The rise and run use to be a minimum tread of 10" and a maximum riser of 8". I admit that this was a very steep stair climb! Today the minimum tread is (and depending on the building inspector) 11" and the maximum rise is 7.5". Although, some building inspectors have allowed a 10.5" tread with a 1/2" nose overhang. Refer to the code book on winder or curved stairs.
• Handrails and Guardrails. There is a difference, but the code is the same. First, the minimum height is 34" above the finished floor. If there is a bottom horizontal rail then it can not be more than 4" above the finished floor. The clear opening between balusters can not be greater than 4". A Handrail is the railing going up a flight of stairs. If the handrail is wall mounted then it will not have balusters. A Guardrail is found at the top of stairs and at balconies and is required when there is a floor elevation difference of 30" or more.

Anyway... before starting the design process for your new Dream Home, or maybe even a room addition, you should telephone your city Building Inspector's office and ask what Building Code, and Year Version are they referring to.