Issue 9 - May 2015

Update 9 provides clarification and further information on technical issues relating to the residential guidance (Repairing and rebuilding houses affected by the Canterbury earthquakes). These issues result from new information or feedback received on the guidance since its publication in December 2012. 

59. Can poly-propylene precast panel shims be used for packing the tops of piles instead of slips of H5 timber?

(Guidance document reference - Part A, section 4)

The use of purpose made poly-propylene precast panel shims as a substitute for an H5 timber packer is acceptable for both Type A and Type B foundations. The poly-propylene shims are colour coded based on thickness. The maximum packing height using precast panel shims for this residential application is 50mm. The minimum number of shims should be used and where more than two shims are used they are to be pinned together at two locations, these being the diagonally opposite corners of the stack of packers.

60. If a house is being relevelled what is the relevelling objective?

(Guidance document reference - Part A, section 2.3)

Extract from Part A section 2.3 page 2.4 (columns 2 and 3 referenced are from to Table 2.3).
“If the floor profile fits within the criteria in column 3, the expectation is that the relevelling processes will result in a floor that is as near as reasonably practical to level and certainly within the criteria stated in column 2 These are the maximums of desired slope and differential displacement, and tighter tolerances should be targeted during relevelling processes.

The indicator criterion of 50mm in Table 2.3 is provided solely as an indicator for initiating a re-level. Finished floor levels are expected to be as close to level as can practically be achieved and re-levellers have indicated that, given the control they have on the lifting process, they will be able to achieve far better than 50mm out of level in most circumstances.

61. What is the required sealant for multi-unit building inter-tenancy walls detailed in Part E (Figures 23.30 and 23.32) of the Residential Guidance?

(Guidance document reference - Part E, section 26.3)

Sealant is only shown generically in Figures 23.30 and 23.32 (partially reproduced below in Figure 1) to detail the junction of a non-rated (fire and/or acoustic) ceiling or wall to a retained firewall. The new ceiling or side walls in the Figures are not fire or acoustic-rated. Therefore the sealant does not need to be either fire- or acoustic-rated and any flexible sealant can be used.

figure 1

Figure 1: Extract from Figure 23.32 from Part E of the Guidance

Sealant is not shown on other details in Part E, but inter-tenancy walls are noted as being “installed to meet minimum FRR of 30/30/30 and minimum STC of 55”. If sealants form a component of a proposed new or rebuilt inter-tenancy wall then the specified sealant must meet both fire and acoustic performance requirements. Where a proprietary inter-tenancy wall system is specified, the sealant that is part of that system must be used.

62. Where a brick veneer cladding is being reinstated are there ways of combining the requirement for cavity drainage and sub-floor ventilation when there are no vents in the perimeter foundation?

(Guidance document reference - Part A, Appendix A)

Often, older brick veneers on Type B foundations had ventilation vents and/or open perpends in the lower courses to allow the cavity behind the veneer to ventilate. The vents also provided a way for air to circulate through the subfloor space if there were no vents in the perimeter foundation because there was no barrier between the two spaces. If the veneer is to be re-built on such a perimeter foundation, it is important that at least the same veneer ventilation configuration and capacity as previously provided is incorporated into the new work to ensure that the previous level of cavity and subfloor ventilation is retained.

If it is unknown or uncertain what the previous veneer ventilation configuration was, and/or you are unable to replicate it, then current building code compliance requirements must be adopted for the new veneer. That compliance can be achieved by either complying with E2/AS1 or by providing an alternative solution complying with Clause E2. Expert advice has indicated that while not allowed under E2/AS1 for new construction, it is acceptable for this reinstatement work to continue with an airway between the cavity and the subfloor space but a link to the roof space is to be avoided.

Dealing with the building wrap

The existing or new building wrap is brought down to the lowest point on the framing without covering the airflow path to the subfloor space. At the top, the wall wrap is turned out over the top of the veneer (or where possible behind) the soffit or in a similar way to close off the roof space from the cavity while still retaining the required ventilation at the top of the veneer. If the top of wall wrap cannot be done with one piece of wrap, an additional section of wrap may need to be lapped to the wall wrap to achieve the seal.

Veneer cavity ventilation and drainage

The veneer cavity ventilation requirements can be achieved by including appropriately sized vents (to E2/AS1, section 9.2.6) in the lower courses of the new veneer and at the top of the veneer. Drainage is provided by leaving the mortar out of vertical perpends of the lowest course (also to E2/AS1) and creating a mortar fillet behind the veneer to force the moisture to flow to the outside.

Subfloor ventilation

Subfloor ventilation requirements are different to cavity ventilation requirements and are calculated in accordance with NZS3604 6.14.1. It is unlikely that the slots for cavity ventilation will be sufficient to also provide ventilation to the subfloor space and additional ventilation grills are required in the lower brick course to achieve the necessary amount of ventilation area.

To illustrate the above, Figures 1 and 2, respectively show cases of bearer at right angles to the perimeter foundation and parallel to the perimeter foundation, and Figure 3 shows options for the top of the veneer cavity.

62 figure 1

 

Figure 1: Ventilation and drainage requirements when bearers at right angles to the wall when no ventilation is provided in the perimeter foundation.

62 figure 2

Figure 2: Ventilation and drainage requirements when bearers parallel to the wall when no ventilation is provided in the perimeter foundation.

62 figure 3

Figure 3: Options for finishing the top of the veneer cavity

Repairing and rebuilding houses affected by the Canterbury earthquakes

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This information is published by the Your home’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: