R401.3

Section R401.3 is titled 'Drainage' and covers requirements for surface storm water drainage away from foundations. Storm water collection methods, direction of surface water drainage relative to the foundation, and amount of grade slope to facilitate drainage is established. The purpose of this section is to prevent structural failure, premature degradation of foundations, and water from entering below grade portions of the dwelling. This section has an exception which allows for an alternate sloping where certain physical arrangements make the required slope of this section infeasible, as well as allowing for a shallower slope across impervious surfaces within a certain distance from the foundation. The purpose of this exception is to allow for practical alternatives where physical infeasibilities exist, and to allow for lesser slopes on patios and similar areas to reduce the chance of slip and fall hazards.

The model shows a dwelling with stormwater draining away from the foundation. A section of an adjoining property has grading that doesn't allow for the dwelling to achieve the standard grade slope away from the foundation, and instead has built swales. Notice that the patio drains more slowly than the adjacent earth since it is allowed a 2% slope per the exception instead of the standard 5% (6"/10'). Note-The allowed exception for the patio, at a point 10' from the dwelling, creates a 3.6" elevation drop to earth grade; the designer should consider if this step-off from the patio is wanted, or if the patio should be designed with a slope that matches the earth grade slope.