Thread: AS1684 and Pad Sizes ????

Chris,

You'll probably need to get your footing sizes designed by an engineer (and receive relevant paperwork) to satisfy your building surveyor.

That said AS1684 determines the pad footing size based on the square metre area that each pad footing is picking up. The maximum size it calls up is 500 dia. x 200 thick (430x430x250 thick). Typically (in Melbourne)pad footings under stumps are around 350-450 dia.

Presumably you will have to get your coucil or bulding surveyor to approve your drawings. If you specify say 300mm dia. and 200mm thick they should then compare to your soil report and let you know if they aren't satisfied.

If you are doing a bit on your extension yourself, then it is well worth investing in AS1864-4, which is the simplified non-cyclonic section of the framing code. It is quite uesful and available for less than $100 from government bookstores.

300 sq with a 150 thick pad would probably be adequate, if holes are round you need to make the 350 diameter, this would apply to standard bearer/joists spacings. I assume you are engaging a draftsman to do your drawings, if you are doing them yourself I urge you to reconsider, if they are done yourself the building surveyor may find so many mistakes that some are bound to slip through the cracks which can cause problems later.

Chris can you clarify the bit referring to the 300mm wide ! !
As the buildingsurv said - 350 diam by 150 thick will cover most situations but it really does depend on the load on the stump i.e. a stump supporting floor load only takes into account the span & spacings of the bearers to determine the pad size. If supporting loadbearing walls the amount of roof load transferred down plus the floor load etc. etc.
If there is a point load from say an internal post supporting a cathedral ceiling then the pad size would be determined by calculating the roof area supported & whether it was steel [ 40kg/m2 ] or a tiled roof [ 60 kg/m2 ]
Your 'building designer' or 'draftsman' should have noted it on the drawings somewhere or from past experience where we've been slack or had a bad day the building surveyor, if he's on the ball, will write it on in large red ink !

Originally Posted by OBBob

If you are doing a bit on your extension yourself, then it is well worth investing in AS1864-4, which is the simplified non-cyclonic section of the framing code. It is quite uesful and available for less than $100 from government bookstores.

I got it for free, who wants a copy?

Possibly the main crux of determining timber sizes comes back to the 'design wind gust speed' for your particular site & if you don't know what this is, then to be blunt don't use the Timber Framing Code.
The simplified [Part 4] part of AS1684 covers only catagory N1 & N2 sites.

Originally Posted by Shaun04

I got it for free, who wants a copy?

me

I'll have a copy as well...thanks.

Thanks for all your advice, i'll put it back on the draughtsman.

FYI, bearers are at 1.5m (bearer span) * 1.7m (joist span) grid with 1 wall only supporting roof which is colorbond and RLW of 3.0.

This site is bloody amazing, thanks for all your help.

Chris

On those figures the floor only pads would be 250 diam by 100 thick
The wall loadbearing pads - 350 diam by 150 thick

Originally Posted by ausdesign

Possibly the main crux of determining timber sizes comes back to the 'design wind gust speed' for your particular site & if you don't know what this is, then to be blunt don't use the Timber Framing Code.
The simplified [Part 4] part of AS1684 covers only catagory N1 & N2 sites.

I got that one aswell.

Who ever wants one just PM me and we'll sort something out.

Originally Posted by thebuildingsurv

300 sq with a 150 thick pad would probably be adequate, if holes are round you need to make the 350 diameter, this would apply to standard bearer/joists spacings. I assume you are engaging a draftsman to do your drawings, if you are doing them yourself I urge you to reconsider, if they are done yourself the building surveyor may find so many mistakes that some are bound to slip through the cracks which can cause problems later.

You hit the nail on the head so to speak Sonny Jim. Hopefully more people listen to your advice because you appear to know your stuff. Tell me, are you a Building Surveyor or is that just a user name? I would attempt to perform a search to find the answer, however i am not too crash hot with computers.

What state are you in? Are you registered with the HIA or Master Builders?

Back to the topic. When considering the soil report, ensure you read the fine print and generic notes produced by the Geotechincal Engineer. It is also wise check that you comply with his recommendations and specifications introduced in the fucntionality index and compaction requirements.

Hopefully this helps...