ABUTMENTS

What length of lead should cover tiles at a top edge abutment?

The Lead Sheet Association Manual contains some very specific recommendations regarding the use of lead for flashing with roof tiles. The basis for these recommendations is that the length of the flashing should be related to a vertical rise of 75 mm.
However it is still a common mistake to interpret the lap as being relative to the rafter pitch rather than the tile pitch. With some tiles the difference between rafter pitch and tile pitch can be as little as 2.5º but with plain tiles it can be as much as 10º. At low pitches the difference between the tile pitch and rafter pitch can increase the length of the flashing by up to 125 mm. This means that at a tile pitch of 30º the length of the flashing over the surface of the tile should be 150 mm. From this point, as the tile pitch reduces, so the length of the flashing should increase until the lowest allowable pitch of 11º is reached. At 11º the length of the flashing must either be 400 mm or completely cover the interlocking tile and turn down the leading edge.
For a typical flat interlocking tile at a 20º rafter pitch, the minimum lap of the lead over the head of the tiles at a top edge abutment would be 285 mm and the minimum lap of the lead up the valley would be 315 mm.

How should lead be fitted to the Top Edge Abutment Ventilator?

The Abutment Ventilation System simplifies the installation of the lead flashing at a top edge by eliminating the need to dress lead over the roll of profiled tiles. One width of lead sheet suits all pitches and profiles of tiles. The tray supports the lead across the gap between the tiles and the wall. The lead sheet should be measured and folded prior to being installed. Trying to dress the fold onto the support tray will result in support tray deformation. The lead should be lapped at adjacent sections by 150 mm. Two layers of code 4 lead can be fitted in the channel on the leading edge. Merely butt jointing the lead will result in leaks.

What is the correct side abutment detail with liner trays?

Liner trays are designed to replace timber rafters typically in industrial and commercial buildings. Tiling battens are normally fixed to 50 x 50 mm counterbattens which are screwed to the crowns of the liner trays. Insulation is installed in the base of the trays. To create a space for a secret gutter at a side abutment an additional 50 x 50 mm batten must be fixed to the side of the final counterbatten. This batten supports the ends of the tiling battens whilst the final counterbatten supports the base of the secret gutter.

What is the correct detail at a raking side abutment?

A raking abutment is one that is not perpendicular to the eaves/ridge line. The detail will be different depending upon whether the eaves length decreases or increases.
Where the eaves length decreases, the ridge or top edge abutment will be longer than the eaves which means that water running down the roof slope will run into the abutment. This is very similar to an inclined valley where the water drains into the valley. Raking abutments of this type should be designed as an open lead valley with one side dressed up the abutment under a step and cover flashing and the other dressed under the tiling with a tilting fillet and welt. The width of the open section of the valley is dependent on the plan area of roof discharging into it, normally between 50 mm and 125 mm. The true pitch of the valley should not be below 11º, this being dictated by the lap of the lead sheet. Where the eaves length increases, the ridge or top edge abutment will be shorter than the eaves. This means that water running down the roof slope will run away from the abutment as it does on a hip. This type of raking abutment should be designed with a lead cover flashing. If the tiles are flat then there should also be a secret gutter. Preformed abutment flashing units are only suitable for standard abutments and are not suitable for either situation. Where insulation is also partially filling the rafters leaving an air gap between the top of the rafters and the insulation, one ventilation tile per rafter space may also be required depending on the below ceiling construction to let ventilation in or out at raking abutments.