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Building codes & compliance

Like to know what wood to use building a pergola or framing a barn? How about the difference between tung oil and polyurethane as a floor finish? How to revive decking or deal with merbau stains? Or how to meet the building code or bushfire standards? Or ask about the environmental advantages of wood or forest certification?

Q. I am seeking advice specifically on Timber construction for residential projects, designing for a framed roof with steel sheeting. The wind class of this site would be N3, could you tell what are or how to determine the hold-down details and specifications for rafters and LVLs that I would need to include in the structural design for this build. It will be a standard brick veneer, single story dwelling.

To specify the timber sizes and tie-down details needed for a roof in a non-cyclonic area with an N3 wind classification you will need a copy of Australian Standard 1684 Part 2, "Residential timber-framed construction". Span tables published as supplements to AS 1684.2 include sizes for N3 areas. Copies of AS 1684.2 can be purchased on line via this link - http://infostore.saiglobal.com/store/getpage.aspx?path=/publishing/shop/promotions/timber.htm&gclid=CMuai4Dpgb4CFUeVvQodW7QAYw. Note that there are four possible versions, a PDF download, a loose-leaf hard copy, ditto in a binder, or bound as a paperback. An Appendix to AS 1684.2 includes guidelines on general building practices associated with engineered wood products such as LVL, but span tables are supplied by the manufacturers. A selection of design software can be downloaded from this site: http://www.woodsolutions.com.au/Articles/Resources/span-tables-software-resources.

Q. I am trying to find a span table or structural member table that will give me stud sizings that will range from 2700mm right up to 3600mm or beyond if it exists. I currently have the AS. 1684.4 tables and they only go up to a stud height of 2700m. Is there a publication that will give me these stud sizes to suit the wall heights higher than 2700mm that I can refer to?

AS 1684.4 is the simplified part of the Code and therefore is limited in some areas. Parts 2 and 3 (Part 3 for cyclonic regions) allow more flexibility than Part 4, but they restrict external wall heights to 3.0m. The span table supplements to AS 1684.2 and AS 1684.3 give stud sizes up to 4.8m, but the 3.0m height limit is imposed so that racking forces and tie-down capacities are not exceeded. However, it is possible to design walls up to 3.6m in height if racking forces and tie-downs are adjusted accordingly. The span table supplements to AS 1684.2 and AS 1684.3 can then be used to size suitable studs. (The reason why the tables extend to 4.8m is to allow for internal walls in houses with cathedral ceilings, ie. not exposed to wind forces.) A User Guide explains this in more detail. It can be downloaded from the Wood Solutions website via this link: http://www.woodsolutions.com.au/Articles/Resources/AS1684-external-wall-heights.

Q. I am doing an extension in a BAL FZ, and finding it a good challenge, but just saw in the DA that the front door needs to be metal and non combustible, have you got a product I can use or point me in the right direction?

Bushfire Attack Level FZ (Flame Zone) applies to areas of extreme risk. However, side-hung external doors are not necessarily required to be metal or non-combustible, unless the local authority has requirements that are additional to the Australian Standard. What the Australian Standard actually requires is for doors to be protected by a bushfire shutter or to comply with the test method in Australian Standard 1530.8.2, "Tests on elements of construction for buildings exposed to simulated bushfire attack - Large flaming sources". A company in Victoria produces ironbark doors and windows that comply with AS 1530.8.2 and you can find out more via this link: http://www.paarhammer.com.au/bushfire.html.

Q. I've been doing some reading about the untreated timber in the building industry and I'm a little uncertain about what I should do in this situation that has prompted me to do this reading. I'm going to build a 2 storey brick veneer house on a concrete slab. I've been getting quotes. From the prefab companies they supply treated pine which is what I thought was generally used by all these days. But I have also considered having the frames built onsite. The prices for onsite including supply of frames came out far cheaper much to my surprise. To my surprise they are using untreated oregon. I questioned him about termite issues and he doesn't see it as a big deal. When I ask about having it treated he suggests using treated timber on the bottom walls and having oregon for the 1 floor up. He has labelled it F7 Oregon. Any advice would be great on this matter.

Using treated timber for house framing (eg. "Blue Pine") is not required by the Building Code of Australia (BCA) and F7 grade oregon is a satisfactory building material. What is mandatory under the BCA is to provide termite barriers in termite risk areas, if the primary building elements (ie. structural components) are at risk of termite attack. Blue Pine and other treated timbers are not at risk of attack and therefore, technically, barrier systems are not required although termite barriers are still useful to keep termites out of the building. Untreated oregon framing would be considered at risk and therefore termite barriers must be installed. If you are building on a concrete slab at ground floor level the slab itself can be designed as a barrier. This requires the slab edge to be set 75mm above adjacent paving to allow termites to be detected if attempting to enter the building. Junctions between different sections of the slab and any slab penetrations (eg. plumbing) must also be protected with a barrier such as TermiMesh. Regarding the idea of using treated timber on the lower storey and untreated timber above, this would be OK if you also had proper termite barriers. However, it would not be satisfactory if there were no termite barriers since termites are capable of crawling over treated timber to reach untreated timber.

Q. We often work with American White Oak as our preferred timber. for Joinery, furniture, and lining panels. We are now up against fire engineering and can't find any information on combustibility to meet with Australian building codes. For this particular species. Can we refer to the American Red Oak? Or do you know of another source? Where I can find this information?

There are various combustibility requirements according to the type of building in which the timber is used, the timber species and other factors. Internal timber wall linings are regulated on the basis of their Material Group, according to the Building Code of Australia's Specification C1.10a. American white oak has been tested and found to fall into Material Group 3 as long as it is used in a thickness of 9mm or more. Perhaps this is the information you need, but if the local authority is calling for something different let us know and we may be able to advise you further.

Q. Are there details available for FRL 90/90/90 timber junctions as with the 60/60/60 ones shown in the Wood Solutions Design Guides? E.g. wall and floor, wall and roof etc.

Boral Plasterboard have a very comprehensive manual for timber-framed Class 2 buildings which includes 90/90/90 systems. You can access the manual via this link: http://www.boral.com.au/brochures/ordering/PDF/10592_Multiframe_Draft_9_RGB.pdf?site=boral&company=Plasterboard. The CSR Gyprock "Red Book" also includes 90/90/90 timber-framed systems and can be accessed via this link: http://flipbook.gyprock.com.au/GyprockTheRedBook/files/assets/seo/page1.html.

Q. Could someone please contact me regarding Class 2 timber construction details.

Our sister website at www.woodsolutions.com.au has a design guide that should help. The following link will take you to where the Design Guides are located: http://www.woodsolutions.com.au/Articles/Resources/Design-Construction-Guides. Since your project is Class 2, Design Guide #2 is the relevant one.

Q. I am an architect and we are designing a multi-storey class 2 building and would like information on wall systems to achieve BCA compliance. Are there current manuals we can review? Also we require a fire rated FRL 60/60/60 external wall in one situation. Is this achievable?

Our sister website at www.woodsolutions.com.au has a design guide that should help. The following link will take you to where the Design Guides are located: http://www.woodsolutions.com.au/Articles/Resources/Design-Construction-Guides. Since your project is Class 2, Design Guide #2 is the relevant one. Regarding the external wall, our understanding is that a timber-framed brick veneer wall where the external brick skin is not less than 90 mm thick will satisfy the regulations for FRL 60/60/60 when tested/certified from the outside (refer Gyprock Red Book) . If you prefer a timber-clad wall, weatherboards fixed over a layer of moisture-resistant fire-grade plasterboard are OK. For details of how to achieve a 60/60/60 FRL using timber cladding over fire-grade plasterboard, refer to the Boral OutRWALL guide. However, note that in some situations Class 2 construction requires external walls to have FRL's of 90/90/90, 90/60/60 or 90/60/30, depending on their distance from a fire source feature.

Q. Pergola (unroofed) framing in Bal 19 and BAL 29 construction. the standard does not specifically deal with pergola framing. Assuming it does not support roof framing does it need to be of bushfire resistant or non combustible material (the dwelling to which it is attached will be mud brick,)

The Australian Standard that specifies the construction of buildings in bushfire-prone areas (AS 3959-2009) does not specifically mention pergolas and similar unroofed structures. Consequently any type of timber can be used. However, note that if the pergola is to have a roof and is also attached or adjacent (closer than 6 m) to the house it would be classed as an "awning roof" and then comes within the scope of AS 3959. So in your case, where the pergola will be unroofed, any timber can be used.

Q. Lintel size !!! I have a window opening 2.3 m, concrete tiled roof . I have used 2/190x45 treated pine H3 LOSP F7 timber with 45mm bearing each end as a lintel, please advise is this adequate .

According to AS 1684 a lintel of 2/190 x 45 spanning 2.3m can support a tiled roof with a "roof load width" of up to 4.5m. So you could have roof trusses with a top chord length of 4.5m including overhang and still be within Code requirements. For lintels the minimum bearing at end supports is 35mm (ie. a stud of normal thickness) so again you are well within limits.

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