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How do you calculate the axial shortening for timber columns in high rise structures?

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Typically the issue is not the column shortening, but the yield under compression perpendicular to the grain of floors/plates, combined with the shrinkage of the same elements. So, the more “horizontal” grain in a given design, the higher the shortening.It is very much related to a given design and loading, so it's difficult to give a generic answer. For more detail on this topic contact Paolo Lavisci here:

When dealing with an old building at least 50 to 60 years old and evaluating some old hard wood timber joist, what would be a safe timber grade to use?


Jack Stevenson

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There are two ways to approach this, but both methods require the species of timber to be identified. Perhaps there is a record of the species, or alternatively a small sample can be taken and sent to a specialist for identification. A suitable person is Dr. Jugo Ilic, email Once the species is known it can be treated as recycled timber and graded to a special set of tables available for download here: Alternatively, timber in an internal environment with a known history and not subjected to heavy, long term loads in the past can be considered to be 1 stress grade lower than that indicated for new timbers, graded using AS 2082, Timber - Hardwood - Visually stress-graded for structural purposes.

Hello, I'm trying to find an engineer or specialist in the field of storm inundation / effects of prolonged soaking of roof trusses (Cypress pine), under the weight of a tile roof (during a hot, wet summer). Following the storm, over a period of 1 year+ or two winters, 1.5mm cracks or tears, opened up beneath areas of inundation. These were approx. 2-3+m in length, at about the halfway point (2.75-3m), either side of the ridgeline (trusses span 11+m). This I believe is the weakest point of a truss. No cracks were present before the storm, and there are no movement cracks from the slab / walls. The brick veneer house dates from 1980-1, and was constructed on sand. No clay is present on site. When the storm occurred, what water that didn't disperse to the rooms or wall cavities, soaked into the insulation either side of the base chords. Black mould subsequently formed, indicating prolonged high moisture retention (proven by a mould expert). It was a particularly hot, wet summer in western NSW that year, and likely resulting in a steamy environment beneath the foil sarking. Since the initial cracking below areas of ingress (foyer, hall, lounge, family), the cracks have not worsened, but new ones have formed. There is minor Gyprock detachment (2-3mm), and the family room ceiling has an obvious 30mm droop. Popped nails are present to the ceilings. New cracks have since formed beside the existing, or in line with the same effected truss. There is also cornice cracking. The issue I've encountered is a lack of understanding or comprehension of the problem. The cracks still continue to open every winter (1.5mm), during cold temperatures, then tightly close in summer. Temperatures in western NSW, can range from a low -5 degrees in winter to 45 degrees in summer. Humidity is generally low, with more moisture present in the air during winter. The roof has no leaks, with the interior tested to have 0 moisture content. This continual opening and closing of the cracks, means that refinishing the Gyprock won't solve the problem, as the cause will simply reopen the cracks in the following winter. The engineers contacted, don't seem to understand the process, as they can't understand contraction in summer and expansion in winter, because they feel it should be the opposite. Regards, John

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In climates that have warm dry summers and cold wet winters timber will shrink in summer and swell in winter. Your engineers may be more familiar with steel which expands when heated and shrinks when cooled. Timber would expand when heated too if it didn't contain moisture. A reference in our library puts it this way: "For timber with a moisture content greater than about 3%, the shrinkage due to moisture loss on heating will be greater than the thermal expansion, with the effect that the net dimensional change on heating will be negative". Timber would only normally have a moisture content of 3% or less when dried in an oven, so for all practical purposes timber shrinks when heated. But technically it is not temperature-related - shrinkage or swelling is a result of a change in moisture content. If you need an engineer familiar with the behavior of timber, we suggest Colin MacKenzie at MacKenzie Consulting, phone 0419 743 081. Colin is based in Queensland.

Seeking advice on the use of Glulam or LVL for the rehabilitation of timber bridges. Any developments on use or dynamic testing of beams for road traffic use.

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We are not aware of any dynamic testing of Australian glulam for use in road bridges, but suggest you contact the Glued Laminated Timber Association of Australia (GLTAA) to explore this further. The GLTAA has a website here: It is also possible that people prominent in the timber engineering community may know of relevant data, for example Prof Keith Crews at the University of Technology Sydney, email:

Hi, I'm looking at using Tasmanian Oak for a highly loaded suspended timber floor over concrete slab, to be designed to the New Zealand standard NZS 3603. Could you please advise the relevant bending and shear strengths in MPa? Also the modulus of elasticity and tension/compression strengths would be useful.

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The characteristic values will depend on the stress grade of the timber. A common stress grade for seasoned Tasmanian oak is F17. Table H2.1 of the Australian timber structures code (AS 1720.1) quotes the following values for F17 grade (all in Mpa): bending 42; tension parallel to grain 25; shear 3.6; compression parallel to grain 34; MOE 14,000. Values for other stress grades can be obtained from Table H2.1.

Hi i have a timber grading from an engineer for pine at F7. If i use hardwood, do i simply need a hardwood product with an F rating above 7?

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Your engineer has calculated that the minimum grade required is F7, so any timber with a grade of F7 or better will do the job. The base grade of Australian hardwood is F8 (there are higher grades) but since F8 material is stronger than F7, then F8 hardwood would be OK.

Hi there, I have had prefinished engineered timber flooring installed for about a year and there are end to end board failures in many areas resulting in vertical movement of these boards. Do you know if this rectification method is acceptable industry standard and is it currently being used in Australia? In addition, there was meant to be a layer of plywood installed between the battens and floorboards. For whatever reason, this plywood layer is missing. The installer has refused to accept the flooring defects are due to this missing supportive plywood layer and is only willing to spot rectify the affected and moving boards by fixing in a long nail to the concrete subfloor and then pouring in glue to push up the sinking boards. I am wondering also whether popping and squeaking noises from loose boards in other areas are caused in relation to the missing layer of plywood. Could you please assist me in recommending someone who is able to carry out destructive testing of the installed boards to investigate whether they are strong enough to withstand residential use when installed directly over battens without a layer of plywood. I am from Adelaide, South Australia. Thank you for your time and assistance.

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Most engineered timber flooring is designed to be laid over a solid base. In your case the proposed rectification method does not sound ideal. We suggest you obtain an installation guide from the manufacturer or importer of the flooring to see how it should be handled. The Australian Timber Flooring Association (ATFA) has published a comprehensive guide to engineered flooring available for download here. The guide points out that "There are a limited number of products that can be fixed direct to joists or battens [ie. without a plywood or particleboard underlay]. For the specifics relating to the preferred installation method, the product supplier’s installation recommendations need to be viewed and then recommendations adhered to".

We are looking at attaching a granny flat to an existing residence and would like some Fire rating options

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Perhaps you could consider the house and the granny flat to be a multi-residential complex with the dividing wall constructed as if it is a Class 1a townhouse development. In this case our Technical Manual 01 would apply. You can download a copy from the Wood Solutions website via this link. Note that you will have to log in first. If the existing external wall to which the granny flat will be attached is brick veneer, the brick skin may well have an adequate FRL (Fire Resistance Level) assuming there are no window or door openings in it. As stated in Technical Manual 01, separating walls must have an FRL not less than 60/60/60. Advice on the fire resistance of brickwork may be available from brick manufacturers. 

i would like to know what the tie down/connection requirements are for a ridge beam to the rafters (where the rafters abut the beam instead of sitting on top).Does table 9.22 or 9.24(A) of AS 1684.2 apply?

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Yes, Table 9.22, details (l), (n) and (o) give three tie-down/connection methods for rafters that abut the ridge beam. These details would apply in a 'cathedral' or exposed beam roof where there are no ceiling joists to tie the lower ends of the rafters.

A non L/B wall by AS1684.2 definition can carry ceiling loads. If you frame above a doorway as per 6.2.3 (a) am i correct in saying this method will carry ceiling joists without a specific designed lintel/hanging beam.

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If a hanging beam lands on a non-loadbearing wall a stud has to be placed under it as per clause If there is no hanging beam, and the ceiling joists are bearing directly onto the non-loadbearing wall, our interpretation is that a lintel is required in accordance with clause In our opinion the doorway can only be framed as per 6.2.3 (a) if the wall is not carrying any ceiling load and the doorway is not wider than 1800mm.

I'm looking to install a deck, half on a concrete slab and the other half on 120x45 joists. I'm planning on putting the part of the deck on the concrete slab on 35mm battens with 1.5mm packers underneath the batten so that water wont pool under deck. The other half of the deck will be on 120x45 joists with about 150-200mm of ground clearance. Question: I can't afford the composite decking so im looking at putting down timber. Wondering what type of timber I should put down on a low deck? The deck area is mostly uncovered too. I was told that merbau is a good choice, but i like the look of the lighter timber such as spotted gum.

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Spotted gum is a good choice for decking as it is a Durability Class 1 timber above ground and has a low tannin content, so causes minimal staining. If your packers are only 1.5mm thick they will easily be blocked by debris so you might consider slightly thicker ones. Other details relating to low level decks are contained in an informative data sheet published by Timber Queensland. It can be downloaded by writing TQL 13 in your browser.

We are Perth-based architects. We are in the process of designing a music shell. We would like to fabricate it from glulam beams and marine ply. Is there anybody in WA fabricating special glulams? Our alternative is to purchase from NZ

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It’s not necessary to go as far afield as New Zealand, producers of glulam are located in the eastern States. You will find a list of Australian producers on the website of Glue Laminated Timber Association of Australia (GLTAA). And although we don’t know of any producers in WA there are certainly suppliers of glulam who have contacts on the east coast, eg. Austim.

fire resistance reports for common wall in Class 1A

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At Wood Solutions we have test reports on the performance of timber products such as floor, wall and ceiling linings, but for actual wall constructions it's best to go the producers of fire resistant linings, such as Gyprock Fyrchek and similar materials. For example, on the Gyprock website you will find resources such as The Red Book which can be downloaded via this link:

I am looking at importing a prefabricated log home. Do you have any advice on this process? Thanks

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The regulations covering the importation of timber products are explained on the Department of Agriculture and Water Resources website here: Scroll down to the tab that says "Logs, log cabins and oversize timber". So far as the performance of the timber under Australian conditions is concerned you will need to reassure yourself that parts of the home that are exposed to the weather and/or termite attack are protected from these hazards. 

My previous deck had a typical balustrade with 3.2mm stainless steel cables passing through 80x80 mm posts (I think they are called rough head posts), with each end of the cable held by a stainless anchor that is screwed into the end posts, and at intermediate posts the cable passes through a 6 mm hole through its center. If a person were to swing or jump on the cable, the mode of failure would simply be an end anchor pulling out of the post. Such a failure could be repaired fairly readily. However, I have recently extended the central section of the deck, so that the steel cable now has three right angles along its path. Where it changes direction, I have drilled a 6mm hole diagonally through the 80 x 80 mm post, from the center of one face to the center of the adjoining face. However, I am concerned that only 1/8th of the cross-sectional area of the post is now supporting the steel cable and that its mode of failure, may be to split the timber by pulling the corner section away from the rest of the post. Are you able to confirm that the intermediate corner posts will still be stronger than typical anchors?

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Very difficult to give you a categorical answer. It sounds as if your posts are softwood if they are "rough headed", rather than hardwood which would be stronger. Also a little difficult to picture the scenario but we gather that the corner posts will now have two 6mm holes at right-angles to one another, close to the same height above the deck thus creating a weak point. We would be inclined to stay on the safe side and reinforce the posts with a galvanised or stainless steel strap fitted tightly around the posts. 

hi Dr. Fred Moshiri,
I recently found out about your research on timber structure from Jane Armstrong and I am deeply inspired by your work.Initially I gained an interest in this subject from working at Taree as a junior engineer. A few questions was raised for me regarding the market for Wood Solutions. Could you kindly comment on the below queries?

How you think wood solution will change engineering?
How would wood structures compare to other structures such as steel (Counsider that fact that Australia is a mining country, it'd be wise to use metal rather than wood?)
How would the cost compare to other structures?(LendLeash shipped their timber from Europe for Barangaroo,Sydney Towers)
What infrastructures do you think would be most suited for wood solutions?
How will the issue of sustainability be tackled by providers of wood solutions?
And finally will there be a seminar soon, I'm keen to listen to your ideas !

Cheers !
Sunny W.

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Dr. Fred Moshiri is actually based at the Timber Development Association, so you will need to contact him there. His LinkedIn profile gives contact details here:

I am puzzled about the relationship between load parameters in the span tables of AS 1684.2  especially as set out in the Timber Solutions v2.2 software package. For instance, at the floor bearers supporting floor load only model of the tables, the software offers the following inputs: 1. Total ground floor load (kg/m2). Preset options up to 100kg/m2 are offered, but any value can be typed in. 2. Floor load pressure (kPa). Preset options up to 5kPa are offered. There is no option to type in alternative values, but reference is made to AS1170.1 and the possibility that the standard may require higher loads in certain circumstances. 3. Floor point load (kN). Preset options up to 7kN are offered. There is no option to type in alternative values, but reference is made to AS1170.1 and the possibility that the standard may require higher loads in certain circumstances. 4. Balcony load pressure (kPa). Preset options of 1.5 and 3.0kPa are offered. There is no option to type in alternative values. I assume this applies just to balconies and is there to distinguish balconies that are more than 1m above the ground. My main question is whether when calculating total floor load (input 1) you need to take account of inputs 2 and / or 3?

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1. The 'ground floor load' up to 100 kg/m² is simply the dead load imposed by the floor material (timber flooring plus tiles, timber flooring plus slate, etc).

2. The 1.5 kPa is the 'floor load pressure' but perhaps more easily understood by the term 'uniformly distributed load', or an older term 'live load', ie. the weight of everything superimposed on, or temporarily attached to, a structure (people, machinery and equipment, furniture, appliances, etc). The preset options in Timber Solutions up to 5 kPa match those in AS 1170.1, varying according to the use of the building.

3. The floor point load (concentrated load) allows for loads that might cause punching or crushing and is applied over an area of 350 mm². AS 1170.1 provides that "distributed and concentrated loads shall be considered separately and design carried out for the most adverse effect", so if you were calculating from first principles you would do it that way.

Timber Solutions does this automatically, so for a house floor it would either be 1.5 kPa or 1.8 kN whichever is more severe. 4. Yes, 1.5 kPa applies to balconies less than 1 m above ground level and 3.0 kPa applies to balconies 1 m or more above ground, simply on the basis that the consequences of failure are more serious for elevated balconies. Note that these loads only apply to balconies in self-contained dwelling - balconies on "other" buildings, eg. office buildings must be designed for 4.0 kPa, and areas susceptible to crowd loads with no fixed seating (eg. a hotel balcony), 5.0 kPa.

Hi WoodSolutions-Team I'm a 5th-semester student at the department of Architecture, Civil and Wood Engineering in Biel, Switzerland. To achieve my engineer's degree according to our school curriculum I'm doing a 9-month traineeship by the company Timberbuilt Solutions in Melbourne. In these time I have to write a thesis which is about the mid-rise timber buildings. I'm just in the beginning and research different timber systems for that. I know that the fire safety is a big thing but it's hard to find good ill-ustrations about that (like details solutions of connections...). Do you have any publications for that? At the moment I can need as much informations as possible to get into this topic. Kind regards, L. Wuersten

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You might find it useful to have a look at our Wood Solutions Technical Design Guides available for download here. Note that you will have to log in to download copies. There is also a Technical Design Guide specifically on mid-rise timber buildings that is number 37 in the series.

Hi. I'm looking for some industry advice on structural timber. We have a 5000sqm glass roof which we would like to support with engineered structural timber that can span approx. 8.5m. We'd like to bring someone into our offices in SYD to discuss. Any advice or supplier contacts would be appreciated.

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The Timber Development Association in Sydney suggests that the following NSW-based engineers would all be up to speed with timber design:

Richard Hough – Arup phone 9320 9453

Paul Davis – Project X phone 4576 1555

Barry Young - TTW phone 9439 7288

You could also contact Timberbuilt, website here:


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