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Chimney flashing - front apron

Sheet Lead Apron

When flashing a chimney the first item to fit is the sheet lead front apron. It is fitted to the lowest part of the chimney where it projects through the roof. Its purpose to weather the transition between roof slate or tile and chimney stack.

The apron can be made from code 4 sheet lead, to suit pitch and width of chimney. Before introducing the apron in position, clip / straps of sheet lead approximately 50 mm wide should be fixed close to the head of the tile or slate and laid with the fall down the roof. Once the apron is positioned the part of the clips / straps can be turned back over the bottom edge of the apron, providing support. This support will maintain the position of the apron, keeping it snug for the longevity of the roof.

Dressing the Lead Apron

The top edge of the apron needs to be weathered and methods for this vary. I prefer to dress the top flat against the chimney, determine the joint in the chimney that i intend to chase out and calculate the width of the cover flashing I need to make. This will simply be a strip of lead folded on one edge a min of 30 mm and have a width that will allow a minimum of 50 mm cover over the apron upstand against the chimney.

It is then fixed into the chase/ joint by lead wedges. The reason I prefer this method is that it allows for any movement / settlement of the roof without adding stress to the sheet lead apron. However if made with sufficient height the top edge can be turned through 90 degrees for a width of 30 mm and let in to a corresponding joint.

Once the chimney has be flashed and wedged, the chased out joints that received the sheet lead must be pointed. This can be done with either sand and cement mortar pointing or lead sealant introduced using a sealant applicator.