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I am making an urgent request about some timber I have been told has a rating of F7. The exporter in Canada states that the timber has not been treated or kiln dried when leaving Canada as it was green. The only treatment was from the builder putting on the base Area that went below ground level some tar like substance. He then placed the timber directly into the ground and filled each footing hole with quick dry cement. He ran out of cement so each footing hole is still half filled. Since doing this it has rained on and off in Orange, NSW for over three days with the holes periodically filling up. This is adding to my concerns.

As an ex ocean sailor who once owned a wooden yacht, I know how quick wood can rot. With the added problem of rain water the rot problem is heightened. Thus, owning a wooden boat does require high ongoing maintenance , I always had to wash down the hewn decks etc with sea water as it was not so harsh. However, this a separate issue and nothing to do with current pergola problem that involves the wood Oregon.

I am concerned about the long term safety and integrity of Oregon being placed directly into the ground and then encased in cement as I would have preferred the timber being placed on stirrups - off and out of the ground where rain water has less chance of causing rot below. I planned to let the Oregon aged naturally but now believe it could be better to paint the wood beams as a form of protection. What do you advise?

In fact can you advise what I should do?

(1) advise the builder to jackhammer the wood out of each hole and use stirrups fittings?

Or

(2) leave things as they are?

I am there looking for advice from you. Then depending on this advice on what each option can provide that will see the timber perform with regards to safety and longevity.

Woodsolutions Answer +

Your timber may be F7 grade but that is a strength rating and does not imply any particular durability or longevity in the ground. In fact Douglas fir, known in Australia as "oregon", is rated Durability Class 4 in ground contact according to Australian Standard 5604, Timber - Natural durability ratings. This suggests a probable life expectancy of up to 5 years. Even out of ground contact, oregon is not a highly durable timber. However, posts that are painted on all surfaces, including the ends, and supported on stirrups, will achieve a longer life above ground than in ground as long as there are no joints where water can collect. Rather than trying to jackhammer the timber out of the ground it would be simpler to cut the posts off, bring the concrete up to a little above ground level and mount the posts on stirrups attached to the concrete pads. You can give the timber some added protection by inserting boron sticks in the base of the posts - refer website here: https://preschem.com/products/timber-protection/no-rot.

Oregon

Answered on 29-10-2020
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

Question

I am designing a deck in 86 x 19 Blackbutt in a BAL 12.5 situation. Timber sub floor in treated pine. The deck will be enclosed. I cannot find direction in relation to the spacing of the decking boards in AS3959. The supplier suggests 86 x 19 Blackbutt should be spaced at 3-4 mm. Builder suggests wider spacings to allow embers to fall through (I don't agree with). Is there any direction in Aus Stds or the NCC please? 

Woodsolutions Answer +

The supplier and builder are both right. AS 3959:2018 advises a gap of 3mm, while acknowledging that a gap of 10mm may stop embers becoming lodged between decking boards. In our opinion a gap of 10mm will trap shoes with small heels and have a 'gappy' look. A gap of 3mm at the time of installation allows for minor swelling during winter and shrinkage during summer. AS 3959 includes the following Commentary clause which is for information and non-mandatory: "Spaced decking is nominally spaced at 3mm (in accordance with standard industry practice); however, due to the nature of timber decking with seasonal changes in moisture content, that spacing may range from 0mm to 5mm during service. It should be noted that recent research studies have shown that gaps at 5mm spacing afford opportunity for embers to become lodged in between timbers, which may contribute to a fire. Larger gap spacing of 10mm may preclude this from happening but such a spacing regime may not be practical for a timber deck." 

Decking

Answered on 29-10-2020
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

Question

I have a client looking for some expert advice as to the condition of some exposed glue laminated beams in Adelaide. In particular I am looking for some expert technical advice as to the likely impact of weathering on glue laminated sections and any potential preventative measures to prolong the performance life.

Woodsolutions Answer +

If your client sends us specific information about the condition of the beams, and the issues that are causing concern, we can respond via this forum. Otherwise, if a site inspection is required we know of a suitably experienced person in Adelaide, but a fee for service would apply. We will send his contact details to your private email address, rather than publishing them on this page.

Glulam

Answered on 08-10-2020
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

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