Code Analysis by Paul

California Residential Code, Section R311.4

Q:  Section R311.4 of the 2010 CRC indicates that habitable levels more than one story above or below an egress door must have a maximum travel distance of 50 feet to a stairway or ramp from that story.  Assuming a flat lot, does this provision apply to a two story building?

A:  No.  

The second story of a dwelling on a flat lot is precisely one story above, not more than one story above the egress door.  In this case, if the dwelling was three stories in height, and again it was located on a flat lot, then the maximum travel distance would be applied to the third story only.   Also, if the two story dwelling had a mezzanine or loft on the second story then this would apply to the mezzanine/loft too.

California Building Code, Vol. 1, Section 502.1

Q1:  The definition of Grade Plane in the 2010 CBC discusses the measurement of elevations when the building is on a flat lot or where the ground level adjacent to the building slopes “away” from the exterior walls.   Does this exclude those cases where the ground may ascend from the exterior walls? 

A1:  The definition is unclear on this. 

The term “away” does imply down or descending from the exterior walls.  As such, where the ground slopes down (away) from the walls one can either measure at a lot line or if the lot line is more than 6 feet from the exterior walls at a point 6 feet from the exterior walls.  Where the ground slope rises (ascends) from the exterior walls, then the first sentence of the definition would apply and the measurement is taken at the exterior walls.

Q2:  In the same definition, the code indicates that the reference plane shall be established by the “lowest” points within the area between the building and the lot line or 6 feet from the building in some cases.   Can a combination of high points and low points be used to define the Grade Plane or just the low points?  Also how many points of elevation are needed?

A2:  Only the lowest points around the exterior walls may be used to define Grade Plane. 

Interestingly, the code doesn’t indicate how many points are needed.  In mathematics, a plane is defined by three points and as such I would use 3 points as a minimum.  It is important to note that this is not rocket science and as such we must remember that this definition helps to set the height of the building.  If the design height pushes up against the code allowable height then perhaps the design team needs to have more elevation points and use a survey.

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