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The Roofing Assoc. Of NZ Has Issued A Set Of Guidelines For Roof Replacement For Homes ....

Submitted by NZMRM Editors on Wed, 13/06/2012 - 12:00am

The Roofing Assoc. of NZ has issued a set of guidelines for roof replacement for homes damaged in Christchurch earthquakes.

The guidelines apply only to work done within the Christchurch City Council jurisdiction and cover timber frames only and give the requirements for the replacement of concrete and clay tiles with profiled metal or metal tiles.

Under Christchurch City Council bylaws this work does not require a building consent but “all building work (whether subject to consent or not) is required to comply with the Building Act, Building Code and all other laws”.

The council also advises that homeowners doing “repairs without building consent” should “keep records of the work done and who carried out the work”.

RANZ recommends that roofing contractors “should take before and after photos of not only the top plate/rafter connection but the purlin/rafter fixings and the fixing method as well. Full documentation of dates, identification of the site must be made and include the specifications of the materials used”.

The RANZ guidelines are:

1.1 TIMBER

In many cases the roofing contractor will be doing the timber upgrade and therefore it is important that both the existing and all the new roof connections are made in accordance with NZS 3604:2011. The wind load will, in some cases, determine the spacing and fixings required but if it is
assumed that truss or rafter centres are at 900mm and that the wind design load is medium = 37m/s = 1.23 kPa (kl =1.5) then.

Trusses and rafters fixed to the top plate must be brought up to the Building Code requirements = 4.7kN capacity.

This will most easily be achieved using purlin cleats and assuming that the original connections are in place and are adequate (2 skewed nails for example) then the addition of 1 Pryda NPPC4 or 1 Mitek CPC40 fixed according to manufacturers instructions per rafter would suffice.

Purlins up to 1200mm spacing – must be fixed with a 1/10g 80mm long purlin screw (minimum) OR a Pryda purlin strap BS 70.

1.2

It should be noted that timber purlins for metal roof cladding are minimum 70mm x 45mm H1.2 <18% moisture content and that battens used previously for tiles must not be used. NOTE:

a)   Cantilevered enclosed decks and exposed skillion roof construction require H3.2 treatment.
b)   Cavity battens require H3.1 treatment.
c)   All other roof framing, including enclosed flat roof framing and associated roof supporting members, valley boards and boards supporting flashings or box gutters, and flashings to roof penetrations and upstands to roof decks require to be H1.2.

Brick chimneys in most cases will already be down but those still standing must be inspected and reinforced or flued before roof cladding replacement is completed.

2.0 PROFILED METAL

ROOFING Roof pitch should be determined prior to profile selection. Refer NZMRM CoP for profile and pitch selections. If corrugate or trapezoidal profile is chosen there are two options of gauge (either 0.40mm and 0.55mm) and their performance under load is given in the load span graphs excerpted from the NZMRM Code of Practice included in this bulletin. It can be seen that for normal application within the Christchurch environs with the use of high strength 0.55mm, intermediate purlin spacings can be up to 1.800mm. with end spans 1.200mm. This can offer a saving in timber, labour and fasteners which can offset the higher cost of the heavier gauge material. If high strength 0.40mm corrugate is used then the usual 0.900mm end and 1.200mm intermediate spacing can be used.  If underlay is run horizontally then the intermediate purlin spacing must be reduced to 1.100mm so that the underlay is ‘captured’ by the fasteners at the purlin. If the site is exposed or on a hillside then the design wind load increases and these purlin spacings should be reduced accordingly. Roof cladding should not be ‘over-fixed’ as this can cause noise particularly if dark colours are chosen and the screw fixing patterns shown with the load span graphs should be used. It is recommended that an eaves flashing is used particularly when plastic spouting is used.

Checklist

  • Identify the site, document dates work was done and specify materials used.
  • Take before and after photos of the job, including top plate/rafter connection, purlin/rafter fixings and fixing method.
  • Make sure that existing and new roof connections comply with Standards New Zealand’s requirements.
  • Ensure trusses and rafters fixed to the top plate are brought up to the Building Code requirements.
  • Battens used previously for tiles must not be re-used