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Re-Roofing

When roof cladding reached a stage that maintenance may cost more than a renewal, a number of decisions will determine if the renewal will require a building consent.

If the material is 'comparable' the contract may not require a consent, but if the decision was made to renew 0.55 mm roof cladding with 0.4 mm material or a different profile it would not be regarded as comparable or "like with like". In this instance, the purlin spacing would have to be changed if it did not comply with the existing wind load requirements.

It is, therefore, recommended that either a consent be applied for or inquiries are made with the BCA or Building Certifier before proceeding with any re-roofing.

Before any existing roof cladding is removed, the surface has to be inspected to ensure it is sound and does not represent a hazard as outlined under safety in section 14.

The provisions for working at height must also be in place before any cladding is removed.

All underlay must be renewed because it is possible that the new cladding material could last 50 years with appropriate maintenance. The underlay support must be inspected, and any material with visible deterioration must be removed and replaced. All old wire netting and staples must be removed before installing new materials. Purlins must be free of debris and other materials, if not the purlins must be turned over or renewed.

Netting must not be used when re-roofing with aluminium cladding; use self-support underlay or alternative underlay support, such as durable synthetic string or strapping.

Flashings must also be renewed when there are different materials involved.

Some older buildings were built with a pitch or purlin spacings that do not comply with the current requirements or the manufacturer's conditions of warranty. The current requirements should be met for consent or before a warranty can be issued. When re-roofing an old tile roof with profiled metal cladding, the battens should be replaced and new purlins installed in compliance with the NZBC.

The roofing contractor is responsible for ensuring that the owner and occupier are fully aware of the work programme. He should advise them to take precautions against temporary water ingress due to the removal of cladding or flashings.

Some factory or essential services may require the roof renewal to be completed outside normal hours or at night. In such cases, the police, alarm companies or other services may have to be notified.

It is the roofing contractors responsibility to make the owner and occupier fully aware of such arrangements and assign the responsibility.

If the old roof or wall cladding has been nailed, the contractor needs to take special care not to damage the ceiling. For this reason screw fixing is better practice.

'Patching' with slip sheets is not a recommended practice, because:

  • it produces transverse laps;
  • it can mix metallic and painted coatings;
  • it is only a short term solution; and
  • it is visually unattractive.

The removal of all material, flashings and other debris is the roofing contractor's responsibility unless otherwise assigned.

Clause: 
014_007_000_000_000_000_000_000_000
Clause Number: 
14.7
/cop/installation/re-roofing
Revision Category: 
0 - Clause Removed
Revision Detail: 

Clause removed. Information absorbed in other clauses.

Draft Clause: 
013_007_000_000_000_000_000_000_000