Checking timber on site — what the inspector looks for

This Issue This is a part of the Timber feature

By - , Build 82

What do building inspectors look for when inspecting building works? The consent process covers inspection of plans through to on-site inspections and issuing the Code Compliance Certificate. Being able to easily identify key components simplifies the process for everyone involved.

Table 1: Sample timber treatment chart for on-site reference.

When building inspectors at Territorial Authorities (TAs) check plans and specifications the first thing they look for is the method the designer has used for compliance, i.e. either the Acceptable Solution using NZS 3602: 2003* or an Alternative Solution.

Most TAs have separate staff for processing building consents and doing field inspections. Therefore, decisions made when processing the consent need to be easily transferred to the field staff, including the reasons behind those decisions.

A field inspector usually has limited time on any particular site and must review a whole raft of issues. For example, at pre-line stage the inspector has to check not only timber treatment but all fixings, lintel sizes, truss fixings, moisture content, dwangs, bracing, building paper, correct laps for cladding, cladding fixings, flashings etc. If this information can be easily and accurately obtained it helps minimise hold-ups on the job.

The Acceptable Solution option

If the Acceptable Solution has been nominated, the designer should note what type of framing is used in each part of the building. The inspector will then check this is in accordance with the standard.

Field inspectors will be checking that the approved timber has been used in each specified location. The markings on each piece of timber will be critical for identifying that the correct timber and treatment have been used.

For most building works a designer or builder will order a house-lot of the greatest treatment required in the worst situation. This doesn’t mean H5 everywhere but if a building has enclosed balconies, for example, then in all probability the house-lot will be H3 rather than a mix of treatments. This approach, while simplistic, can help prevent costly mistakes that may only be picked up well down the track.

Although most inspectors take a systematic approach, they all carry out inspections slightly differently but checking on timber treatment and marking/branding will become another part of the inspection regime. (See pages 52–53 for more on identifying timber treatments.)

Alternative Solutions

If a designer has chosen an Alternative Solution, then further supporting evidence is required. This can include:

• the relevant building code clauses, which must include B2 Durability

• any performance criteria

• establishment of proof, i.e. use of calculation or test methods

• comparison with an Acceptable Solution or product

• existing determinations on a similar proposal/method

• use of proprietary products

• in-service history

• local environmental conditions

• expert supporting evidence.

Using checklists

To make this task as easy as possible it may help to use a checklist as shown in Table 1. This checklist is filled in by the designer who nominates whether they are complying with the Acceptable Solution or an Alternative Solution. If an Alternative Solution is proposed the designer will submit supporting evidence.

The consent inspector can quickly check the design and attach this sheet to the field documents. The field inspector will then know exactly what was proposed and agreed on. The advantage for the builder is an assurance that the council/certifier has agreed to a particular method and that all parties understand what is required. Confusion and misinformation have no place in our industry.

* The recently released NZS 3602: 2003 ‘Timber and wood-based products for use in building’ supersedes NZS 3602: 1995 and came into effect on 1 April 2004. The BIA has since stated that all buildings issued under the old standard will have a period of 1 year to complete the work. After 1 April 2004 all new work must use NZS 3602: 2003 as the means of compliance
Table 1: Sample timber treatment chart for on-site reference.

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Table 1: Sample timber treatment chart for on-site reference.