Abutments

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

Again the answer depends on the type of flashing being used.

When using lead, 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 150mm. 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.

When using a lead-alternative flashing the manufacturer of the flashing should be consulted for their instructions. In the case of Redland Rapid Flashing the flashing material should be fitted into the channel on the leading edge first before dressing and chasing into the wall. An alternative method is to use two widths of Rapid Flashing – one fitted into the leading edge of the tray; the other dressed and chased into the wall. In this method the two widths are then joined and sealed together using the self-fusing properties of Rapid Flashing to complete the cover flashing and make it weathertight.

 

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 50mm 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 50mm 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 is shorter or longer than the ridge length.
Where the eaves length is shorter, 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 50mm and 125mm. 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 is longer, 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.