Since May 2019, the revised test standard for NCC 2019, C1.10, regarding the fire rating of internal linings or materials, has been confusing architects, builders, and contractors as to how they should determine if a timber lining product is Fire Group 1, 2, 3 or 4, or even non-combustible.
There are two main reasons for this confusion.
Firstly, timber has traditionally been regarded as a “safe” product, which requires minimal certification to comply. However, the NCC 2019 does not give natural timber, timber batten or panel products any special status or easier route to compliance, even though it is used in large quantities for many purposes in construction.
Secondly, NCC 2019 refers to AS5637.1, which is a new standard to the timber industry, and it is this new standard which now legislates for a full room burn test for any timber product with “joints” or “openings”. This thus brings to account any timber product except for butt jointed flat panels and slats.
Any timber product with gaps between slats or beams, or holes, perforations and other openings in a timber finished panel, requires a full room burn test ISO 9705. The traditional small scale Cone Test AS3837 is no longer acceptable, although some manufacturers are still offering it.
The effect the regulators are wanting to avoid is premature flashover, that is flashover that occurs while persons are still exiting the building, or flashover that occurs before the fire engine has arrived. Flashover is considered the point when the heat of the fire in an ISO 9705 test room reaches 100Mw.
Joints and openings reduce the time it takes for the fire to reach this heat level for the following reasons:
- Joints and opening in timber products allow extra heat to penetrate more rapidly into the substrate.
- Openings, holes, and slots allow for greater airflow though the material, and this increased oxygen increases combustion.
- Timber products char off relatively quickly after initial combustion, but this charring off effect creates more heat which accelerates the overall combustion process due to the additional surface area of the joints and openings.
Supawood has found that fire retarded timber products will generally return a Fire Group 2 result. Non-fire-retarded timber products will generally return a Fire Group 3 result.
Fire Group 1 is hard to obtain in a timber product, but this is still possible, and Supawood has achieved this with a few of its products.
To make matters even more complicated, in some areas, the only compliant product is neither Fire Group 1, 2, 3 or 4. Instead yet another category of compliance must be reached called non-combustibility.
This now introduces the large number of requests for a “non-combustible” certificate, which is fair enough. However, most non-combustible materials are already listed in the BCA as being “deemed” non-combustible, and includes some materials which are partly combustible, like plasterboard.
The full list of acceptable (“deemed”) materials given by the BCA in Part C1.9 is as follows:
- Perforated gypsum lath with a normal paper finish
- Fibrous-plaster sheet
- Fibre-reinforced cement sheeting
- Pre-finished metal sheeting having a combustible surface finish not exceeding 1mm thickness and where the Spread-of-Flame Index of the product is not greater than 0.
- Sarking-type materials that do not exceed 1mm in thickness and have a Flammability Index not greater than 5.
- Bonded laminated materials
Aluminium is the most versatile material for creating non-combustible products, and therefore Supawood also offer all its products in a woodgrain powder coat version on aluminium. This finish is provided with a certificate to show that it also meets the requirement of having a Spread-of-Flame Index of zero.
For yet another added complication, clause 7 in C1.10, allows for Building Surveyors to regard decorative timber linings or materials that are suspended under another ceiling, or fixed over another wall lining, to be regarded as an “attachment”, or “other material”.
In this instance, all other Fire Group classifications fall away, and a very old interior test standard, AS1530.3 is referenced, with the stipulated minimum result called for being a Spread-of-flame index of 9, and a Smoke-developed index of 8 if the Spread of flame is more than 5.
The decision on whether to regard a decorative lining as being an attachment/ other material, or as a wall or ceiling, is totally dependent on the Building Surveyor for the project.
Although this test standard (AS1530.3) is not as onerous as the new AS5637.1, because it is an old standard, many suppliers no longer have their test certificates, and can only give you the results off their brochures. This may or may not be acceptable to the Building Surveyor.
Another Clause, Part C1.10 (c), lists items that are exempt from the requirements of Fire Group testing, including:
- Timber-framed windows
- Solid timber handrail or skirting
- Timber-faced door
- An electrical switch, socket-outlet, cover plate, etc
- Paint, varnish, lacquer, or similar finish, other than nitro-cellulose lacquer.
- A joinery unit, cupboard, shelving, or the like.
- Any other material that does not significantly increase the hazards of fire (how on earth do you determine this?)
The above is not just confusing and ambiguous for designers and construction personnel - building surveyors and certifiers have a very similar problem.
Generally, building surveyors are trying to be strict in their interpretation of the BCA, without being unreasonable. Of course, because of the subjectivity of interpretation, you end up with a range of opinions from being overzealous to being somewhat lax. These inconsistencies don’t help make it any easier for those in the construction industry.
Read more about what building certifiers struggle with here:
Taking this all into account, an architect, designer, builder, or installer thus has two choices:
- Collaborate with knowledgeable suppliers like Supawood to advise you on your fire compliance for your project, ensuring you only specify correctly fire rated or classified products.
- Take the risk of specifying a non-compliant product, which could end up coming back at you up to 6, 7, or 10 years later, depending on whether you are an architect or a builder, and which state law you and your project come under.
Supawood looks forward to helping you with your upcoming feature lining needs, allowing you to get home and rest easy - knowing that your project is compliant.