24 CFR Part 100—Fair Housing Accessibility Guidelines, Preamble

(d) Outside surface at entry door.

The final Guidelines also provide that at the primary entry door to a dwelling units with direct exterior access, outside landing surfaces constructed of impervious materials such as concrete, brick, or flagstone should be no more than 1/2 inch below the interior of the dwelling unit. The Guidelines further provide that the finished surface of this area, located immediately outside the entry door, may be sloped for drainage, but the sloping may be no more than 1/8 inch per foot.