Waterproofing
Overview
Waterproofing refers to systems and practices used to prevent liquid water from entering building assemblies. The objective is continuity of the waterproof layer at joints, penetrations, and transitions so that water is routed away from susceptible materials. Failures are typically costly because repairs often require destructive access or replacement of finishes and substrates.
Common materials and systems
Typical waterproofing approaches include sheet membranes (bituminous, polymer-based, or thermoplastic sheets), liquid-applied membranes (elastomeric coatings or polyurethane), cementitious treatments for confined wet areas, and preformed flashings. Selection depends on exposure, substrate, expected movement, UV exposure, and constructability. Membrane choice also depends on compatibility with adjacent materials and finishes.
Key detailing areas
Continuity is most critical at:
- Joints between dissimilar materials (expansion joints, control joints)
- Wall-to-floor and deck-to-wall transitions
- Pipe and service penetrations
- Drains, scuppers, and gutters
- Terminations at parapets, windows, and doors
Details usually include priming, flanged flashings, reinforcing at corners, and secure mechanical or bonded terminations to maintain positive drainage.
Installation sequencing and compatibility
Waterproofing installation commonly follows substrate preparation: cleaning, leveling, and priming. It is common practice to sequence roofing or deck waterproofing before finishes that depend on the waterproof layer. Compatibility with adhesives, sealants, and adjacent coatings should be confirmed. Temporary protection after installation is important to avoid damage during subsequent trades.
Inspection, maintenance, and repair
Regular inspection is recommended after installation and at scheduled intervals. Inspections typically focus on ponding water, blisters or delamination, failed terminations, and clogged drains. Maintenance often involves clearing drainage paths, resealing exposed joints, and replacing localized membrane areas. Repairs depend on system type; liquid membranes may be patched, while sheet membranes often require partial replacement and re-detailing.
Common causes of failure
Failures commonly arise from inadequate detailing at transitions, poor substrate preparation, thermal or structural movement beyond the system’s capacity, improper material compatibility, and lack of ongoing maintenance. Ponding water and mechanical damage from trades are frequent contributors.
Design considerations
Designers typically coordinate waterproofing with roof slope and drainage, substrate tolerances, and access for inspection. Durable details at penetrations and terminations, wet-area fall to drains, and selection of materials suitable for UV or traffic exposure are common practice to reduce lifecycle risk.
Used in stages
See also
FAQ
Transitions and penetrations are the most critical. Wall-to-floor, deck-to-wall, drain connections, and service penetrations require reinforced flashings and secure terminations to maintain continuity. Expansion and control joints also need appropriate accommodation or joint systems.
Inspection frequency depends on exposure and use but common practice is an initial inspection after installation, then periodic checks—often annually or after severe weather. High-use or roof areas with equipment may require more frequent inspections.
Repairability depends on system type and extent of damage. Small punctures or localized delamination may be patched, particularly with liquid-applied systems. Extensive failures or damage to laps and terminations often require removal and replacement of affected membrane sections.