Folding flashings

By - , Build 102

Flashings are in the frontline of the building weathertightness battle. Here are a few useful details to help that fight.

Figure 1: Flashing around end of barge board.
Figure 2: Barge board flashing showing cut and fold lines.
Figure 3: Folding flashing around the end of the barge board. Steps 1, 2 and 3.
Figure 4: Apron flashing at roof/wall junction.
Figure 5: Apron flashing showing cut and folding lines.

Arecent discussion with a plumber/roofing contractor about metal roof flashing turned into an origami demonstration when, with a few deft cuts and folds of A4 size sheets of paper, he demonstrated some of the details that he has found to be effective.

Figure 1: Flashing around end of barge board.

Barge flashing

The first was a barge flashing detail. Typically, a barge flashing is folded over the profiled metal roofing and down the face of the barge board, finishing with a drip edge. But what happens at the bottom of the barge flashing? Generally nothing – it is simply stopped, leaving the exposed end grain of the timber barge board.

Figure 2: Barge board flashing showing cut and fold lines.
Figure 3: Folding flashing around the end of the barge board. Steps 1, 2 and 3.

A simple solution providing considerably more protection to the end of the timber is shown in Figure 1. By cutting and folding the flashing around the end of the timber, a neat, protective capping is created. It may be pop-riveted and sealed to finish the detail. Figures 2 and 3 show the sequence of cutting and folding.

Figure 4: Apron flashing at roof/wall junction.

Apron flashing

The second detail was of an apron flashing at a roof/wall junction, a frequent point of water entry into the building structure. In order to improve the weathertightness, the water from the roof should be directed away from the junction. Proprietary apron diverters are available for this, but the same result can be achieved with a few folds of the apron flashing itself. Figure 4 shows how this can be done.

Figure 5: Apron flashing showing cut and folding lines.

Figures 4 and 5 show where the metal flashing must be cut and folded. Fold A is between the apron (over the roofing) and the upstand (behind the cavity battens and cladding). A cut (cut 1) is made parallel to the fold and two more cuts (cuts 2 and 3) are at 45º to the fold. The flashing is folded at 45º inwards at fold B in a continuation of cut 2, and folded at 45º outwards at fold C continuing along cut 3. The tabs created by these cuts slide underneath the ‘apron’ creating the kick in the flashing upstand that directs water away from the wall junction. The tabs must be riveted and sealed under the ‘apron’.

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Figure 1: Flashing around end of barge board.
Figure 2: Barge board flashing showing cut and fold lines.
Figure 3: Folding flashing around the end of the barge board. Steps 1, 2 and 3.
Figure 4: Apron flashing at roof/wall junction.
Figure 5: Apron flashing showing cut and folding lines.

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