As water may drain down or be held by the wall underlay, it is fundamental that builders install the underlay to ensure that it forms an impervious drainage plane that stops water getting to the vulnerable bulk insulation or timber frame.
Wall underlay must be installed taut, laps must have sufficient cover and should be taped, any penetration or tear must be taped and sealed and the underlay must exit the assembly at openings that will allow water to drain out.
For cavity claddings, an additional batten or taut tape is required for battens spaced at more than 450 mm to hold underlay in place and prevent it billowing into the cavity.
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Scribing to bevel-back weatherboards (see below for the six steps).
Step 1. Tack the scriber blank to the side of the facing board. Make sure it is 75 mm or so overlength. A handy hint is to remove the head of a panel pin and drive it home as the fixing.This means that there is nothing to get in the way of the marking process.
Step 2. Using the leaf of a builder’s rule, transfer the profile of the face of the weatherboard to your scriber.
Step 3. Turn the ruler 90º and mark the underside of the weatherboard.
Step 4. Set your jigsaw to undercut.
Step 5. Note that both cuts are undercut in opposing directions so it is more efficient to do one cut on each scriber before changing the blade angle. In other words, do the short cuts on one scriber and the long cuts on the other, then change.
Step 6. Trim the top off the scriber by the same amount as you have been off-setting the short cut and trial fit. Adjust by trimming any 'mouth' that doesn’t fit well. Fit again and trim bottom of scriber to fit. Prime and finally fix.