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Ironwood fire resistance & timber fire ratings

Fire Resistance and Fire Ratings

Of course we have made it a point to enjoy ourselves at work over the last 12 months. What you may not have realised is that we have new management, some new staff and have made a concerted effort to improve what we do and how we go about servicing our customers.

We know that in business image is very important. What's more important to us however is backing the talk up with experienced staff, quality products, great service. We intend to continue working on these goals during the next 12 months and look forward to meeting or talking to you.

...and because it is already December, we at Ironwood would like to wish our customers a merry Christmas and happy New Year. Oh, and one other thing, we will be closed from 12:30pm on 23 December over Christmas and New Year and will be back at work on 5 January 2004.

Message for architects, designers and renovators

Timber floors appreciate, carpets depreciate - you've heard that before! What's new however is that old goes with new and reusable products are in vogue with modern design trends. These are just a few of the reasons why timber flooring is much sought after. It is reusable, can be brought back to life and there are a 101 other reasons why people prefer natural products.

Interior design and decor is constantly evolving. It seems that it is also maturing now that decorators and designers are looking to mix a range of old and natural elements in their designs. The look of a newly cut and polished recycled timber floor is fantastic. Have a look in the latest Trends magazine.

Keith Mackenzie
Managing Director

December specials!

See our fantastic range of Tempe recycled floors and feature posts - HUGE DISCOUNTS on their intial release.

Feature story
Fire Resistance and Timber Fire Ratings

Here in Australia we have some of the harshest climatic extremes on the planet and also some of the most expansive and flammable forests. At this time of year it is therefore poignant to reflect on the fire resistance of various timbers - without getting too carried away with the technical stuff.

There is no denying that hardwood flooring and timber beams will of course suffer damage in a fire. Surprising as it may seem, certain Australian species exhibit an unusual resistance to flame spread, depending on the temperatures to which it is exposed, the duration of heating and thickness of the timber. Many of you would be aware of this having seen that large hardwood timber sections are extremely difficult to light in your fireplaces. They also often char on the outside and then extinguish themselves - the charred material effectively protecting the core from further damage.

Our Australian standard measures whether a timber ignites within 10 minutes of being exposed to a designated heat level (10kW/m²) and the level of heat it radiates over a period of 10 minutes after being exposed to 25kW/m² (i.e. measuring its capacity to smoulder). These head loads were set having regard to the Ash Wednesday bush fires. Obviously these lab tests also take into account factors such as moisture content, thickness of the sample, timber density and angle of the exposed grain.

An independent study conducted for the National Timber Development Council rated various timbers as follows:

Best performers
(classified for construction purposes as 'Fire-Retardant-Treated' timbers)

  • Blackbutt
  • Merbau (Kwila)
  • Red Ironbark
  • River Red Gum
  • Silver Top Ash
  • Spotted Gum
  • Turpentine

Not so good performers

  • Forest Red Gum
  • Jarrah
  • Tallowwood
  • Yellow Stringybark
Poorest performers in the test sample
  • Hoop Pine
  • Mountain Ash
  • Messmate
  • Radiata Pine

The relevance and applicability of the 'Fire-Retardant-Treated' timbers classification is that when homes are built in bush-fire prone areas, Australian Standards regulate what exposed timbers and construction materials require fire-retardant treatments. What is of particular interest is that although chemical fire retardant treatments are available we are not aware of any applications which have been tested and rated in accordance with the Standard! These tests would require accelerated weathering testing. This is where the hardwoods work so well - they require no maintenance and they provide long term fire performance.

Obviously using the right timber is therefore highly relevant and having timbers which are less susceptible to ignite is imperative in certain locations.

Standards Australia AS3959 - 1999 adopts the following site assessment classifications of the potential risks associated with bush fires (having regard to the type of vegetation, distance from vegetation and slope of the land) and regulatory practices:

Low risk - no additional building requirements apply.
Medium risk - construction required to avoid ember attack.
High risk - construction required to resist radiant heat and flame attack.
Extreme risk - beyond the application of any regulation.

Generally the Standard does not impose any special requirements on interior timbers, including wall and roof framing. Exposed sub-floor timbers, less than 600mm from the ground in medium and high-risk areas need to be treated with fire retardant or constructed with 'fire-retardant-treated' timbers. Bearers and joists for decks have limited requirements, while outdoor pergolas are not subject to the Standard.

With medium risk buildings, timbers can be used for exterior cladding, window frames, eaves, fascia, decking and exposed posts provided they are treated with fire retardant or constructed with 'fire-retardant-treated' timbers.

Two methods of applying the fire retardant to timbers are available: - a) brushing or spraying; or b) pressure impregnation. Pressure impregnation is required on timbers which are exposed or subject to wear and tear, whereas coatings are applied in areas that are protected or under cover.

Additional information is available at:
http://www.timber.net.au/search.asp (search word is "bushfire").

Species Colour Hardness
Strength Group
Alpine Ash # Light straw 5 4 SD4
Mountain Ash # Light straw 4.9 4 SD3
Blackbutt Pale yellowish brown 9.2 2 SD2
Box - Grey Dark browns & reds 13.1 1 SD1
Brush Box Pinkish grey/reds/20 browns 9.1 3 SD3
Ironbark - Grey Dark browns & reds 16.3 1 SD1
Ironbark - Red Dark reds 14.0 1 SD3
Kauri - N.Z. Pale pink/reddish brown 3.3 4 SD8
Karri - W.A. Pink/dark reddish brown 9.0 3 SD2
Mahogany - Red Dark red 12.0 1 SD3
Messmate # Yellowish to greyish brown 7.1 3 SD3
Pines - Baltic White/pale yellow 2.5 4 SD8
Pines - Cypress Pale/dark yellow 6.6 4 SD6
Spotted Gum Pale to dark browns 11.0 2 SD2
Sydney Blue Gum Dark pink to red brown 9.0 3 SD3
Tallowwood Yellowish brown/olive 20 tinge 8.6 1 SD2
Turpentine Dark pink to reddish brown 12.0 1 SD3

#1 These Ash/Messmate varieties are = collectively and=20 commonly referred to as either Victorian Ash or Tasmanian=20 Oak.

#2 Some of the above ratings are subjective as = there are=20 considerable discrepancies depending on which text is used = to source=20 the above data.

N.B:- When it comes to structural = beams=20 and posts strength, toughness, elasticity, shrinkage, = weight,=20 stability, lyctid borer susceptibility, edge splintering, = plus a few=20 other industry measurements details can be accessed via the=20 internet. With Ironwood's feature beams and posts they have = usually=20 been modified by their previous fitting and age - we = therefore do=20 not attempt to rate these beams ourselves as they are sold = primarily=20 for aesthetic purposes.

Our warehouse and display rooms are conveniently located in Rozelle (near the ANZAC Bridge). Come in and visit us, we are open Mon-Fri 7:30 a.m. - 5:00 p.m. and Saturday 9:00 a.m. - 3:00 p.m

© 2003 Australian Ironwood Antique Timbers Pty Ltd. All rights reserved.

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