Browse Forums Owner Builder Forum 1 May 29, 2018 4:34 pm Hi all, I've got my engineering for my garage slab back and I'm a little concerned that the engineer might be overly conservative, potentially costing me more. For the purpose of this, I'm building a 7mx6m garage. On a Class P soil site. I have a sewage easement on the back fence line, it is 1.8m wide, which I am building on the boundary. There is a sewage pipe 2.7m deep in the middle of it along it's length. 1. Along the back 6m (easement) and down the LH side (boundary), I have to put in 8 off 450 dia x 2m deep bored piers. 2. Specified slab thickness is 120mm 3. 4 off edge beams are 600mm deep and 300mm wide. 4. 2 off stiffener beams are again 600mm deep and 300mm wide. 5. F82 mesh top and F72 mesh bottom 6. 0.2mm thick ploy membrane. 7. Concrete is 20 Mpa For me, this is way overkill for a timber/clad garage with a pitched roof. I've queried the soil test guy, he said site would have been Class M except for some fill and trees. Also spoke to the engineer and he told me as the trees are in the zone of influence and with the sewage easement (pipe is 2.75m deeps) he has no choice, regulations require him to protect the slab. For me, he is being over conservative, he did admit he could have got away with maybe 500mm edge beams, but at the end of the day 600mm is not that much extra. I wonder how much this one is going to cost. Anyone else build anything similar recently? I'm guessing years ago a simple slab of about 100mm or so with simpler footings would have sufficed. Thanks. Re: Slab for garage - is engineer over engineering it? 2May 30, 2018 9:16 am fab4272 You're in luck I am a Engineer & Concrete Contractor & It Sounds about right to me, materials cost $3.5-$4K Excluding ( optional sand pad?) labour 2 days + plant You could use a 100 mm thick slab instead of 120 mm slab and save $4/m2 + mesh but 1 check with your engineer OT Instead of questioning what Trusted Professional Engineers say, Try scrutinizing the Builders & Subcontractors quotes Goodluck Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab for garage - is engineer over engineering it? 3May 30, 2018 8:24 pm Thanks StructuralIBIMGuy,, Yes, you're right. It does sound about right. Doesn't look that much bigger than a std raft slab for an M Class site from the regulations book. I checked with my engineer about the edge and stiffening beams being 600mm deep and why they couldn't be less, but as it is a class P site that was the reason. 120mm vs 100mm slab would mean about 0.7m2 in concrete, not a big difference for my slab size. Also, yes, there is a sand pad as well. Definitely will be scrutinizing the quotes. They are crazy right now. I'm getting anywhere from $15,000 to $20,000 for the complete job. The highest quote didn't include removal of excess soil either. Do you think these prices sound about right? These prices are working out at $325 to $395 a m2. Granted, not a simple 100mm slab, but for those I can have it at $70-$100 m2. I estimated originally it should cost no more that $10,000 I have a flat as a tack site with no problems with access. Only this it will most likely need a line concrete pump for the concrete. Need to get a few more quotes to be sure. Re: Slab for garage - is engineer over engineering it? 4May 30, 2018 8:52 pm fab4272 Definitely will be scrutinizing the quotes. They are crazy right now. I'm getting anywhere from $15,000 to $20,000 for the complete job. The highest quote didn't include removal of excess soil either. Do you think these prices sound about right? I estimated originally it should cost no more that $10,000 $10k for a few days work is Bulldust Ned Kelly & Co (grano workers) are alive and doing well in victoria You can definitely get those prices down..Your estimate is fair Alternatively, Watch a few YouTube videos, Plan it thoroughly (3 weekends job), get a few mates around the more the merrier, Imported Beer & Fillet Steak BBQ after.. that's if you are up to it. Cheers Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab for garage - is engineer over engineering it? 5May 31, 2018 2:18 am Not sure if it is helpful, but I have recently ran across this resource: http://concretebroker.com.au/ May be makes sense getting in touch with them to check if they can source some good concreters for you. Re: Slab for garage - is engineer over engineering it? 6May 31, 2018 9:49 am Thanks for the Link Alexp79 Concrete broker says it all.. US Marketing Spin at it's worse here's why 1. The industry doesn't need another level of commissions and chargers.. building is expensive enough as it is 2. More images about nothing important... where the data & Proofs? 3. People don't trust concretors then add salesman to the mix, hence Two negatives will never make a positive in this instance It's laughable when retired concretors (with bad backs) try to expose/cleanup the industry they were once part of... what next Siteworks Brokers...are the battlers and punters that stupid? sorry for the rant Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab for garage - is engineer over engineering it? 7May 31, 2018 11:06 am I agree, it is a bit wierd-ish. However, main question still stays - how to find good granos and how much you should be expecting to pay for the labour (formwork, steelwork, finishing), e.g. per sqm? Is this article here has anything to do with the reality? https://www.concretebroker.com.au/Blog/View/160 Re: Slab for garage - is engineer over engineering it? 8May 31, 2018 11:36 am Thats funny Joan & Paul who feature in Concrete brokers, star as well in What to wear for your engagement photos do people trust them.. you judge that for yourself If anything the website has seized on some of the pitfalls in building I doubt they deliver anything tangible? Alexp79 I wish I was in a better position to help, if anyone needs assistance in perth leave a PM formwork, steel fixing is easy diy, i can assist with finishing. cheers Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab for garage - is engineer over engineering it? 11Jun 06, 2018 12:06 pm IMO those spec are ridiculous, 4 off edge beams are 600mm deep and 300mm wide plus 2 off stiffener beams are again 600mm deep and 300mm wide. What do you drive a Panzerkampfwagen VIII Maus, it is the heaviest fully enclosed armoured fighting vehicle ever built. Re: Slab for garage - is engineer over engineering it? 12Jun 07, 2018 12:25 pm I queried the engineer on those as well. Unfortunately, I'm on a P Class site, with tree's within the zone of influence, hence the deeper footings. He also used the soil report as a guide for the footings. Granted, I think the stiffeners could have been smaller. Still think they need to be mindful that there desire to add more for the sake of it costs their clients money. Re: Slab for garage - is engineer over engineering it? 13Jun 07, 2018 2:19 pm It would be interesting to know what footings he'd be specing if it was his block, you'd have to believe 450 x 450 would do the job and more to stay on the safe side. A posting from another site to give you an idea of what I think of those specs, you might find this post informative. yep an interesting article, my block has been classified P in an AS soil test report, just been estimated $40,00 for piers etc. Interesting thing for me is its an old suburb built in the 1960s, its full of houses built without the benefit if piers etc, My family owns 5 houses within 100 meters of the site, my nephew lives next door on a 60 year old brick veneer house without any cracks and all the floors etc are level. My mother across the road in a weatherboard place. The block only became available because the existing house burnt down. how did those guys build those houses 60 years ago without piers and they stood the test of time. Are we building the pyramids? something to last a 1000 years? if its $ 40,000 for the footings it will put building out of our reach , it more than 20% of the building cost. Concrete didn't come into use before the 1940's in Australia if you believe records, how have all those building from federation and post federation on class C soil lasted without concrete footings, many of those building are phenomenal when it comes to the build quality. Re: Slab for garage - is engineer over engineering it? 14Jun 08, 2018 12:47 am As far as I know, piers are needed for unstable soils or soils having uncontrolled fill. I have P class slab due to trees around, while the soil classification is M and it is on 3 m slope with very stiff clay soil of around 2-3 m to the rock bedding below. One engineer has designed my slab with 60 piers, 550 mm deep strip footings with concrete-filled blocks on top and 150 mm slab. Based on friends recommendations, I showed this design and my soil report to another principal structural engineer from a decent sized engineering company and after seeing my soil report he instantly said that my slab is over-engineered. Yes, I had to pay extra to redo my engineering, but I ended up with zero piers, 250 mm strip footings and 100 mm slab (also with concrete-filled blocks on top of them). Yes, I had to spend few K extra on my engineering, but have saved at least $15K on extra concrete, reo, piers, escavation, etc., so it is certainly worth it. I advice to show your soil report and ask some more engineers whether things can be improved (PM me if you need details of this engineering company I used - they have engineers in every state). Re: Slab for garage - is engineer over engineering it? 15Jun 08, 2018 6:56 am Hey John1920 I like the Building Information Model (BIM) Engineering but may I suggest more Data and Proofs that are relevant on this site (to House Building?) Rendered Images without Data are useless on most building sites.. OT...I treat this site like my own building site The Battlers & Punters come first...HTH OT Regarding Mining Engineering I do have an interest ( 5 Generations of Engineering) , you might want to reach out on my google community Cheers Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab for garage - is engineer over engineering it? 16Jun 08, 2018 10:20 pm alexp79 As far as I know, piers are needed for unstable soils or soils having uncontrolled fill. I have P class slab due to trees around, while the soil classification is M and it is on 3 m slope with very stiff clay soil of around 2-3 m to the rock bedding below. One engineer has designed my slab with 60 piers, 550 mm deep strip footings with concrete-filled blocks on top and 150 mm slab. Based on friends recommendations, I showed this design and my soil report to another principal structural engineer from a decent sized engineering company and after seeing my soil report he instantly said that my slab is over-engineered. Yes, I had to pay extra to redo my engineering, but I ended up with zero piers, 250 mm strip footings and 100 mm slab (also with concrete-filled blocks on top of them). Yes, I had to spend few K extra on my engineering, but have saved at least $15K on extra concrete, reo, piers, escavation, etc., so it is certainly worth it. I advice to show your soil report and ask some more engineers whether things can be improved (PM me if you need details of this engineering company I used - they have engineers in every state). How do you know your slab now hasn't been under engineered? What was the reasoning behind using piers in the first place? I would ask the original engineer why they designed with piers.Cheaper isn't always correct. Re: Slab for garage - is engineer over engineering it? 17Jun 09, 2018 2:17 am insider alexp79 As far as I know, piers are needed for unstable soils or soils having uncontrolled fill. I have P class slab due to trees around, while the soil classification is M and it is on 3 m slope with very stiff clay soil of around 2-3 m to the rock bedding below. One engineer has designed my slab with 60 piers, 550 mm deep strip footings with concrete-filled blocks on top and 150 mm slab. Based on friends recommendations, I showed this design and my soil report to another principal structural engineer from a decent sized engineering company and after seeing my soil report he instantly said that my slab is over-engineered. Yes, I had to pay extra to redo my engineering, but I ended up with zero piers, 250 mm strip footings and 100 mm slab (also with concrete-filled blocks on top of them). Yes, I had to spend few K extra on my engineering, but have saved at least $15K on extra concrete, reo, piers, escavation, etc., so it is certainly worth it. I advice to show your soil report and ask some more engineers whether things can be improved (PM me if you need details of this engineering company I used - they have engineers in every state). How do you know your slab now hasn't been under engineered? What was the reasoning behind using piers in the first place? I would ask the original engineer why they designed with piers.Cheaper isn't always correct. Well, the new engineering job itself is definitely not cheaper (actually, costs 2x more). They are putting their business reputation, legal and financial responsibilities at stake here, hence, under engineering is highly unlikely. It is still much more highly likely that engineers will over-engineer then under-engineer those days. Also, I am building with Nexcem/Durisol ICF and this particular engineer has a lot of experience with this type of technology and have designed few dozen houses already, so I have more grounds to trust him rather than the previous one, who most probably designed footings to full masonry standards. Re: Slab for garage - is engineer over engineering it? 18Jun 09, 2018 7:37 am Ok sounds like you have confidence in the engineer.The only reason I say this is because I have seen a lot of slabs fail due to tree drying effect without piers and very few with properly designed piers. Re: Slab for garage - is engineer over engineering it? 19Jun 09, 2018 9:00 am alexp79 They are putting their business reputation, legal and financial responsibilities at stake here, hence, under engineering is highly unlikely. It is still much more highly likely that engineers will over-engineer then under-engineer those days. Also, I am building with Nexcem/Durisol ICF and this particular engineer has a lot of experience with this type of technology and have designed few dozen houses already, so I have more grounds to trust him rather than the previous one, who most probably designed footings to full masonry standards. The new Engineers act will also protect Punters from New technologies and internet marketing Spin. If anyone wants a list of failed technologies with data and proofs from an Engineer that specialises in Structural Repairs please leave a PM.. (Forewarned is forearmed) OT Engineers are generally conservative that is why society TRUSTS them Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Slab for garage - is engineer over engineering it? 20Jun 10, 2018 12:50 am StructuralBIMGuy alexp79 They are putting their business reputation, legal and financial responsibilities at stake here, hence, under engineering is highly unlikely. It is still much more highly likely that engineers will over-engineer then under-engineer those days. Also, I am building with Nexcem/Durisol ICF and this particular engineer has a lot of experience with this type of technology and have designed few dozen houses already, so I have more grounds to trust him rather than the previous one, who most probably designed footings to full masonry standards. The new Engineers act will also protect Punters from New technologies and internet marketing Spin. If anyone wants a list of failed technologies with data and proofs from an Engineer that specialises in Structural Repairs please leave a PM.. (Forewarned is forearmed) OT Engineers are generally conservative that is why society TRUSTS them On the other side, engineering is not a rocket science after all, pretty much everything can be modelled and calculated, the physics and formulas around modern structural engineering is well known for ages. Engineers in other countries design and help to build modern houses on 70 degree slopes without too much worries and use some of the "modern" technologies for centures (e.g. in my case, there is nothing new in woodcrete or arbolite on its own and even less new when using it as a formwork for reinforced concrete (in ICF style)). I have seen couple of companies who even 3D print houses with some special reinforced plastic. I am not really sure if "protecting from new technologies" is something Australia really needs. E.g. in the US recently a couple of building "startups" have disrupted the whole industry, I can see it easily happening in Australia too - there are already brick laying robots which can lay bricks faster and better (Australian start up by the way), rendering machines which can render 1000 sq m a day and with a better quality. I really can't see any single reason why robots won't be able to replace 80-90% of the remaining tradies as well as building material production jobs in 3-5 years. But yes, there and always will be cowboys in any industry and there will be always failing technologies. We should be doing our best to learn from the past experiences, but simply rejecting anything new and innovative and claiming it an "internet marketing spin" is never an option. Only engineers which were able to think out of the box and move forward with innovations are responsible for the progress of the humanity, after all. PS. And yes, on the below photo, a post mortem of Katrina hurricane, this is the house engineered and built with "new technologies" in mind, while the houses around it were designed and built by "conservative" guys. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Just my 2 cents, please do not take anything personally. 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