|By Philip O’Sullivan|
|The Building Industry Authority has recently published the new Acceptable Solution E2/AS1. I had the privilege of being on the Working Group. The BIA has also recently published documents requiring treatment of timber framing (B2/AS1) and a test or Verification Method for lightweight wall claddings (E2/VM1)The Building Code tells us what a building must achieve. It’s the boney skeleton hanging off the backbone of the Building Act. More detailed and specific documents such as Acceptable Solutions and Verification Methods give us the final shape and form.|
|A New Benchmark|
|E2/AS1 has set a new benchmark. It is based upon testing, research, experience and consultation. If E2/AS1 is specified with a building consent, then it becomes mandatory. In reality a designer can rely on E2/AS1 to provide the system and many of the details.The designer may need to provide details for certain junctions, just like an engineer designs a beam for a house.|
Councils have become strict over weathertightness, but not without good reason. Standards had slipped, certain cladding systems weren’t robust and the loss of treated timber was the last straw. Councils will develop their understanding over time so hopefully a realistic approach will supercede the current levels of paranoia.
What we all have to realise is that with the move back to treated timber and the use of cavities, our buildings will be much more robust. The key is to do the basics right, and then to focus attention onto risk areas such as balconies.
Some architects will no longer design balconies over enclosed areas as they will always be prone to leaks.
One interesting thing is that with greater prescription we are seeing much more innovation. Both are driven by need, but the innovators now have something to aim for.
|I originated the risk matrix concept in 2001. A bar graph from British Columbia had clearly shown the relationship between eave width and leaks. There were other risk factors, but little information. I analysed 50 sites comprising 300 households that had experienced varying degrees of leakage. Ken McGunnigle from Prendos helped with some acoustic sound advice and Winstone Wallboards gave financial assistance.The most startling thing was the wind zone was less important than first thought. Building complexity, which is difficult to define, is the greatest risk, but that’s obvious. Most leaks occur at junctions; the greater the number and more complicated, the more failures. (for more info http://www.cinz.org.nz – 2002 CINZ Science Forum).|
I thought some sort of table or matrix could be a useful tool, so I adopted a numerical approach that mimics Winstone’s simple method for calculating wind load for bracing.
Subsequent studies by BRANZ and the BIA using WHRS data supported my findings. The approach was then further refined by the BIA to allow different claddings at different risk levels. The benefits of the risk matrix approach in BIA Determinations, is an early sign this approach is sensible and I’m sure it will improve over time.
|Once you get use to cavities, they’re easy. They’re also cheap ? it’s amazing the difference a few battens can make.The key points are:|
E2/AS1 is not the last word. It is a vast improvement and it will improve over time. Every builder, roofer and cladding installer needs a copy. At $6 for a downloaded PDF or $35 for a nicely printed version, there’s no excuse.
The Victoria University Book Centre in Wellington sells the Approved Documents. These documents are available in three formats: hard copy, CD-ROM, and PDF files downloaded via the internet.