Window Sills -
Typical Lug and Slip Sills

The details on the following sheet explain that brick coursing tables should be used to determine heights of sills in order to eliminate costly field adjustments of surrounding bricks.

When determining the height of Cast Stone:

  • The bottom of the sill to the bottom of the lintel must always equal brick coursing.
  • The lintel height (if stone) equals brick coursing minus one joint.
  • The sill height equals brick coursing to the bottom of the lintel, minus the overall window dimension.
  • The height of the lug must equal brick coursing minus one joint.

Lug sills are sills that project into the brickwork at either side of the masonry. This projecting is generally in lengths corresponding to a full or half brick length. Lug sills must be set in place prior to any masonry work surrounding the opening since the masonry rests on the sill lug. All lug sills are recommended to be jointed, regardless of length, due to loading on the lug ends.

Slip sills have no lug and the lengths are figured 1/2” less than the brick masonry opening (for a 1/4” mortar joint) or 2/4” less where sealant is desired to provide a 3/8” joint for gun-in of sealant. The advantage of slip sills is that they may be set in place after all masonry work has been completed, therefore minimizing potential damage during construction.

Drips are provided on sills where 1”+ projections occur, to stop water from returning to the wall. Drips are terminated 1/2” from the edge of the masonry opening where the end of the sill is exposed to view.


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