Registered Building Surveyor, Phil O’Sullivan has a warning, and recommendation, for those who have been affected by the recent floods, and damage to their properties.
While flooding is NZ’s most frequent natural disaster, buildings were never designed for this; the goal has been to prevent flooding in the first instance by a combination of drainage and overland flow. However, the recent floods have overwhelmed whole catchments which is a problem central and local government need to resolve.
The unfortunate use of non-durable Radiata pine framing from 1993 to 2011 affects around 400,000 homes, so many flood-affected owners and those repairing their homes now face an added problem.
Traditionally flood restoration involves the removal of affected contents, floor coverings, wall linings, insulation, and kitchen and bathroom fittings. Our native timbers, boric (boron) treated pine and even particle board flooring can withstand temporary wetting and later drying. Untreated Radiata pine is much less durable than particle board flooring. Once this framing is wet, decay will quickly follow.
The key message, for affected homes and buildings constructed between January 1993 and July 2005, and beyond (refer below), is to remove affected wall linings from at least one side and apply boron treatment to the available faces of the moisture affected framing, while it is still wet. This dampness allows the boron salts to deeply penetrate the timber and to kill the fungi causing the decay.
The cost of treating timber this way is not great, but if damp at-risk pine framing is not protected the cost of latter repairs could be horrendous. So, this is an issue for homeowners, their insurers, assessors, and builders to resolve.
Issues such as wall-bracing, and fire-separation where applicable, needs consideration. For more general flood restoration information refer to the BRANZ Bulletin 666 – Restoring a home after flood damage (2021).
Boron treatment is a soluble salt which uses moisture to penetrate the non-durable sapwood of Radiata pine. Protim Framesaver (boron salt in glycol) is a tested and proven in situ boron treatment used during leaky building remediation for treating soundframing left in place. It has been assessed by Scion (formerly Forest Research) and approved by the Department of Building and Housing (DBH) – now MBIE. For further information refer to the DBH – Dealing with timber in leaky buildings document.
Boron was chosen in the 1950s by the then DSIR to treat Radiata pine framing as it is both an effective insecticide and fungicide; it is cost-effective, relatively safe, and easy to apply. Prior to 1993 most Radiata pine timber framing was wet boric treated.
From January 1993 to 1996 Radiata pine was treated and then kiln-dried. The kiln drying drove out the water and most of the boron salts with it; while low levels of boron remained, the durability of this timber was reduced.
Unfortunately, kiln dried untreated Radiata pine framing (KDUT) was allowed by Standards NZ in late 1995 and then by the Building Industry Authority from February 1998 until April 2004 for wall, floor, balcony, and roof framing. Subfloor joists had to be treated, but only with an insecticide from 1995 to 2004, so these would also be vulnerable to decay.
KDUT became the dominant timber framing during this period. It is vulnerable to a range of rapid and destructive brown rots. This loss of fungicidal treatment significantly lowered the moisture threshold for decay, so it became a major contributor to failure in our leaky buildings.
Between April 2004 and April 2011 KDUT was still allowed for internal wall framing, to upper floor joists and to wall framing behind brick (veneer) cladding. A modern brick & tile house built in 2010 is at risk. So are the internal walls to other houses.
For two & three storey apartments, that have been through leaky building remediation, the internal walls would still contain untreated pine framing.
Since April 2011, all framing timber is required to be fully treated and once again boron has become the dominant timber treatment.
Phil O’Sullivan
Phil is a Registered Building Surveyor, ex Director and now Consultant with Prendos. He and his brother Greg are the acknowledged whistleblowers for the leaky building crisis. Phil is a Past-President and now a Life Member of the NZIBS. He was a workgroup member for: DBH Acceptable Solution (weathertightness) E2/AS1 Third Edition July 2005; DBH/BRANZ Guide to leaky building remediation; and DBH – Dealing with timber in leaky buildings.