The unsung hero of masonry, a properly designed window sill with a continuous drip edge intercepts and diverts water before it damages your wall system.
A masonry window sill has one primary function: to intercept water running down the wall face and direct it away from the building before it enters the wall system. When properly designed, projecting beyond the wall face, sloping downward at 10–15°, and featuring a continuous drip edge underneath, a sill can protect the wall below for decades with no intervention.
When sills fail, through improper material selection, missing drip edges, poor slope, or simple deterioration, water runs directly down the face of the wall and is drawn into the masonry by capillary action. In Ottawa's climate, with approximately 60 freeze-thaw cycles per year near 0°C, this is the beginning of serious ongoing damage to everything below the window opening.
Materials to avoid: Clay brick and standard CMU absorb moisture readily. Used as sill units, they stain, spall, and transmit water into the wall. We specify dense, purpose-appropriate materials for every sill installation.
We replace deteriorated or improperly designed window sills with properly proportioned stone or dense precast units, installed with the correct slope, projection, and drip edge detail. We also repair existing sills where the substrate is sound, repointing, sealing, and restoring the profile where appropriate.
For homes with multiple deteriorated sills, we can typically complete an entire house in a single mobilization, minimizing disruption and cost.
Window sill repair and replacement throughout Ottawa, Kanata, Orleans, Gloucester, Barrhaven, Stittsville, and Rockland. Call for a free assessment, no deposit, no obligation.
