More questions from the floor of the 'You Asked' seminar series

BRANZ answers more questions from the recent 'You Asked' seminar series.

As I have a nominal 20 mm cavity, does it really matter if the cladding leaks?

Yes it does. E2/AS1 is based on a nominal 20 mm dry cavity that is there to deal with any unintended leaks and requires claddings to be weathertight. Any regular leak may affect the durability of materials within the cavity such as H3.1-treated timber battens.

Can original window head flashing details for timber windows installed into bevel-back weatherboards be used where a new addition is to match the existing construction?

Yes they can, but such use will need to be submitted for consent as an alternative method. Part of the supporting evidence will need to show that the existing details have been working and that they will be replicated exactly.

Where do you measure edge distance for fixings into concrete slabs to and from?

Measure the edge distance from the outside face of the concrete or concrete masonry to the centre of the fixing. Edge distance for fixings should not be confused with the concrete cover requirement, which is measured from the face of the concrete to the nearest point of the fixing or reinforcing steel.

Has asbestos fibre ever been used in plasterboard stopping compounds?

Not as far as we are aware, but it may be present in some textured ceiling finishes.

Can cavity battens be structurally fixed to the framing so that the length of the cladding fixings can be reduced?

Yes. Timber cavity battens can be fixed in accordance with BRANZ Bulletin 475 Structurally fixed cavity battens and be submitted for consent as an alternative method. The cladding fixings are as described for direct-fixed cladding in Table 24 of E2/AS1.

What are the key differences between an E2/AS1 rigid underlay and a rigid air barrier?

E2/AS1 rigid underlays are a generic sheet product (such as fibre-cement and plywood sheets with butted joints) that is overlaid with a flexible wall underlay. Under E2/AS1, using a rigid air barrier is a requirement in an extra high wind zone.

Rigid air barriers, which are not covered by E2/AS1, are a proprietary air-barrier system that may be coated and has flashed or taped joints. To be considered an air barrier, a product or system should have a measured airtightness that exceeds 0.1 MNs/m3.

Can softboard be used as a rigid wall underlay under E2/AS1?

No. Only 6 mm fibre-cement or 7.5 mm plywood can be used.

Can a veranda beam be cantilevered under NZS 3604?

Only if specifically designed by an engineer.

How do cavities deal with construction moisture?

It is dried by the ventilation that occurs.

Is a 40 mm deep cavity for claddings other than masonry veneer better than a 20 mm deep one?

Not really. BRANZ research has found that there is more than sufficient ventilation and cladding separation to prevent moisture bridging the cavity in a well constructed nominal 20 mm dry cavity.

Published in building.