Garage Slope

[Jeff Zehnder]

Just looked a home with a detached garage that was part of the inspection. The detached garage had a flat and mostly level slab and was not sloped. Since I do not see that many detached garages...is it OK to have a flat floor?

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[H.G. Watson, Sr.]

Just looked a home with a detached garage that was part of the inspection. The detached garage had a flat and mostly level slab and was not sloped. Since I do not see that many detached garages...is it OK to have a flat floor?

Referenced (quoted & cited) 2009 IRC unammended, below, for your convenience. Suggest you check local code ammendments/adoptions applicable to the subject of your inquiry.

In general a mostly level is not flat, and flat is not sloped and/or crowned to protect walls & plates from vehicular leaks, drainage, and/or transported weather,snow,wash-water, etc. Only the area of floor used for parking is addressed. IIRC NC does not specify the minimum slope required, 2% or otherwise, or any requirement for a singular plane or that the sloped area have any contiguous continuity in the slope(s) of the parking area.

SECTION R309 GARAGES AND CARPORTS

R309.1 Floor surface. Garage floor surfaces shall be of approved noncombustible material.

The area of floor used for parking of automobiles or other vehicles shall be sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway. (emphasis mine)

See also Table R301.2(1), and then Sections R309.3 & R322 if applicable.

R309.3 Flood hazard areas. For buildings located in flood hazard areas as established by Table R301.2(1), garage floors shall be:

1. Elevated to or above the design flood elevation as determined in Section R322 ; or
2. Located below the design flood elevation provided they are at or above grade on at least one side, are used solely for parking, building access or storage, meet the requirements of Section R322 and are otherwise constructed in accordance with this code.

HTH to get you started.