Investigation of Waterproofing Problems in Flat Roof Structures in Residential Buildings in Abuja

Flat roof failures resulting in internal water damage are among the most commonly reported building defects in residential buildings in Abuja, Federal Capital Territory, attributable to the prevalence of poorly designed and constructed concrete flat roof waterproofing systems. This study investigates the nature, frequency, and root causes of waterproofing failures in flat-roofed residential buildings in three Abuja districts: Wuse, Garki, and Gwarinpa. A field-based investigation of 50 flat-roofed buildings identified through referral from building owners and facility managers was conducted. Building age, roof finish type, drainage provision, expansion joint design, and maintenance history were documented. Destructive and non-destructive testing was used to assess waterproofing membrane integrity at selected failure locations. Occupant interviews quantified the frequency and economic impact of water ingress. Results indicate that ponding water due to inadequate falls is the primary cause of failure in 58 percent of cases. Membrane cracking at expansion joints due to inadequate thermal movement provision is responsible for 24 percent of failures. Chemical degradation of bituminous membranes exposed to ultraviolet radiation is a secondary but significant factor. Mean time to first waterproofing failure from construction is 6.4 years. The study recommends minimum roof fall specifications of 1:80, mandatory expansion joints at maximum 6-metre centres, and performance-specified waterproofing systems rather than prescriptive material specifications in Abuja building regulations.

Keywords: flat roof waterproofing, building defects, water ingress, Abuja, Federal Capital Territory