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AS2870 Site Classification

AS2870 Site Classification

AS2870 Site Classification

I typically get asked to quote to design residential projects consisting of small granny flats up to 2-3 storey houses. These foundations are typically designed in accordance with the Australian Standard AS2870 Residential Slabs and Footings. As I am a structural engineer I understand from the code that the classification of the site should be undertaken by someone who has geotechnical experience. So I usually request a geotechnical report even for the granny flats and single storey extensions as I would not back my knowledge of geotechnical matters. I have found though that when I have got geotechnical engineers to quote the quotes range from $600 to $2,000 for a granny flat. This usually results in the client going with someone cheaper, who for some reason doesn't require a geotech report. Has anyone else come across this and how do you get the information you require to get a classification for a site. I am based in Sydney.

RE: AS2870 Site Classification

I am in Queensland so can't say that I have herd of of a way of getting a classification without visiting site. appendix D does allow you to get a roughs but is no means a substitute for a site visit in my opinion.

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

RE: AS2870 Site Classification

I am in Perth. I would say that for projects such as extensions and granny flats you can possibly ask the client to provide structural drawings of the existing buildings on the site and extrapolate from those as to what the site classification is. Also ask if there is any cracking in the walls of the existing buildings. In AS2870 you are allowed to base your site classification on the condition of nearby buildings and their details.

In respect to new dwellings, a 'geotech report' is typically only required for large buildings such as new large three storey houses etc where there is considerable risk. What you want for smaller buildings is a 'site classification report' which should be cheaper (typically around $500). The difference is that a geotech report can be pages and pages of useless information that is not required for small dwellings, whereas a site class report is only a single page stating the site classification in accordance with AS2870. State in your contract with the client that: if the site classification report exposes underlying soil complexity/issues then a full geotechnical report will be recommended. This note would cover sites such as P class where you would need additional information.

If anyone else has other experience then it would be good to hear it.

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