What Is Exterior Foundation Waterproofing? A Complete Guide
Exterior foundation waterproofing is the process of excavating around a home's foundation, applying a waterproof membrane, and installing a drainage system to permanently redirect water away from the structure.
Why Exterior Is Better Than Interior
Interior drainage systems (sump pumps, interior drain tile) manage water after it enters the structure. Exterior waterproofing prevents water from reaching the foundation wall in the first place.
The difference: interior systems manage a symptom. Exterior systems address the cause.
The Exterior Waterproofing Process
Step 1: Excavation
The area alongside the foundation is excavated to the footing, typically 6–10 feet deep for most residential basements. This exposes the full exterior face of the foundation wall.
Step 2: Wall Preparation
The exposed foundation wall is cleaned, cracks are filled, and any deteriorated parging is removed.
Step 3: Membrane Application
A waterproof membrane is applied to the foundation wall. Common types:
- Rubberized asphalt: Traditional and reliable, applied hot or cold
- HDPE drainage board: Modern dimple-mat systems that create an air gap and direct water down
- Spray-applied polyurethane: Seamless, flexible, excellent adhesion
Step 4: Drainage Tile
Perforated pipe (weeping tile) is installed at footing level, wrapped in filter fabric and surrounded by clear crushed stone. The pipe collects water and directs it away from the foundation, to daylight or to a sump.
Step 5: Backfill and Grading
The excavation is backfilled with clean, compacted material. The grade is set to slope away from the foundation (a minimum 6-inch drop over 10 feet is recommended by Ontario building code).
How Long Does Exterior Waterproofing Last?
A quality exterior waterproofing installation should last 20–30 years or more. The membrane and drainage tile are the long-term components; the excavation itself is a permanent correction.
Typical Project Scope
Most residential waterproofing projects involve one or two walls: the wet wall and its neighbours. Full perimeter waterproofing is less common but may be necessary in severe cases.
Contact us for a free on-site assessment. We provide exterior waterproofing across Oshawa, Whitby, Ajax, Pickering and all of Durham Region.