E2/AS1 gives specific minimum dimensions for the gap between the bottom of a cladding and an apron flashing - 35 mm is specified. Where claddings are in contact with flashings, capillary action can result in water being drawn up behind the cladding. Table 7 gives dimensions for most other flashings likely to be used for up to the extra high wind zone.
As well as capillary action forcing water behind the cladding, other common problems with flashings that can result in water getting into the building are:
- incorrect lap or cover dimensions
- incorrect lap direction
- lapped joint failure
- no stop-ends to raking apron flashings around flashings chased into concrete and concrete masonry
- insufficient clearance between the cladding and the flashing - E2/AS1 specifies 35 mm minimum
- fixing method creates holes.
Where all cladding is being removed, flashing replacement is an easy task, and new flashings can be installed with the wall underlay being lapped over the flashing upstand (or the upstand can be taped).
Where cladding is not being replaced, modifying the existing cladding to give the required gap is difficult because:
- there might not be enough upstand to give the required 35 mm cladding overlap to the upstand once the bottom of the cladding has been cut back
- where the cladding is not being removed, it is almost impossible (without the removal of some of the cladding) to insert a new flashing up behind the wall underlay and create the required overlap without damaging the underlay – this also exposes the bottom edge of the cladding, which is difficult to adequately refinish
- danger of cutting through or damaging the flashing during cladding removal.
Updated: 9 September 2014