Browse Forums Building A New House Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 22Jan 14, 2019 6:22 pm Current State: Slab/Frame/Bricklayer/Lockup/Lining/Stairs/Kitchen/Wet flooring/Painted/PCI/Got the Keys My Thread: Building Windsor 40 with Eden Brae (Caddens) Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 28Feb 06, 2019 11:31 am Mark Armstrong BSc (Eng) MIEAust CPEng Development Manager http://www.katanafoundations.com.au http://www.polyvoid.com.au http://www.biax.com.au Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 30Feb 06, 2019 1:38 pm Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 31Feb 06, 2019 2:21 pm Mark Armstrong BSc (Eng) MIEAust CPEng Development Manager http://www.katanafoundations.com.au http://www.polyvoid.com.au http://www.biax.com.au Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 35Feb 06, 2019 4:08 pm Great points - the theory is that a waffle is structurally stiff and can span over some differential movement in the slab - in practice however I agree, where there is poor building practice and if you have an E class site the waffle should not be used. If you have the potential for trees, drainage to affect the slab, then the waffle will be more prone to this than a raft. As a minimum, figure 3.4 in AS2870 should be consulted for your build - I have attached this for those that are interested. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Mark Armstrong BSc (Eng) MIEAust CPEng Development Manager http://www.katanafoundations.com.au http://www.polyvoid.com.au http://www.biax.com.au Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 36Feb 06, 2019 4:33 pm Keeping the void formers in place before and during the pour can be an issue. Gawd, there were some horrible pics of former displacement in a waffle pour on this forum recently. Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 37Feb 06, 2019 6:59 pm insider Engineer AS2870 - the Residential slabs and footings code has several "deem to comply" slabs. Deemed to comply means that engineers can follow the code and get it right, hopefully 100% of the time. The slabs are: Stiffened raft - footings in the ground but footings and slab poured together Footing slab - footings in the ground but slab poured separately from the slab Waffle rafts - slab poured on the ground level with polystyrene pods separated so beams typically at 1.1m form between the pods Stiffened slab with deep edge beams Section 4 of the code allows engineers to design any slab system, but they have to comply with certain differential deflection depending on the type of wall construction...clad frame (the most flexible) through to full masonry (the most inflexible) The uncertainty with anything in the ground is the cost uncertainty for everyone, who knows how well the trenches will be dug, will rain collapse the trenches, will they be over excavated, will soft pockets be found. They are also potentially unsafer from a worker point of view to construct. Along comes waffle and gives everyone a simpler and more cost certain outcome with similar if not better structural performance - this is the main reason waffle has been so successful as a slab system. The reason they are so popular are they are cheaper than stiffened raft.Due to so many failures particularly in the western suburbs engineers have been starting to do hybrid slabs with an excavated deepened edge beam in an attempt to stop moisture ingress under the slab. The waffles have several major problems. *Granular bedding material (used to be scoria) which allows moisture to spread under the slab. *The block has to be perfectly flat usually causing drainage issues especially in highly reactive sites. *You don't get to check if the soil test results are correct as there is no excavation.Soft spots, tree roots and obstructions are never exposed during trench excavations. *"E" reactive sites are often called "H2" because once it is an "E" you can't use a waffle.If you constantly call sites "E" you will lose volume builders because they only want waffles.You may say well to bad the site is what it is and I agree with this but the fact is it influences what geotech's are prepared to say so waffles are put on "E" sites. All this anecdotal talk is fun but where is the long term scientific evidence? We all know the waffle slab disaster of the late noughties when the longest drought in Victorian history broke etc and all the waffle pods heaved and Metricon getting sued etc, but that all coincided with Metricon becoming the biggest project builder in Australia, so of course they had the biggest exposure. Plus they were building on poorly classified land, which hadn't been tested thoroughly enough. Since then the standards have been upgraded to find a compromise that suits builders and engineers. Let's see the results of a proper scientific survey before we try and scare people eh? Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 38Feb 06, 2019 7:07 pm I don't believe proper scientific research is something which can be done here, what will be study protocol and methodology like? And how much it will cost? I would say that if building-expert, who have inspected 1000s of houses, says that waffles on clay tend to me much riskier to heave and require more maintenance, then it is likely to be so. It also pretty well aligns with the theory - waffles have much higher odds of getting heave due to bad drainage or maintenance due to the fact that it is much easier for the water to get under slab. Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 39Feb 06, 2019 7:43 pm sweetswisssteel insider Engineer AS2870 - the Residential slabs and footings code has several "deem to comply" slabs. Deemed to comply means that engineers can follow the code and get it right, hopefully 100% of the time. The slabs are: Stiffened raft - footings in the ground but footings and slab poured together Footing slab - footings in the ground but slab poured separately from the slab Waffle rafts - slab poured on the ground level with polystyrene pods separated so beams typically at 1.1m form between the pods Stiffened slab with deep edge beams Section 4 of the code allows engineers to design any slab system, but they have to comply with certain differential deflection depending on the type of wall construction...clad frame (the most flexible) through to full masonry (the most inflexible) The uncertainty with anything in the ground is the cost uncertainty for everyone, who knows how well the trenches will be dug, will rain collapse the trenches, will they be over excavated, will soft pockets be found. They are also potentially unsafer from a worker point of view to construct. Along comes waffle and gives everyone a simpler and more cost certain outcome with similar if not better structural performance - this is the main reason waffle has been so successful as a slab system. The reason they are so popular are they are cheaper than stiffened raft.Due to so many failures particularly in the western suburbs engineers have been starting to do hybrid slabs with an excavated deepened edge beam in an attempt to stop moisture ingress under the slab. The waffles have several major problems. *Granular bedding material (used to be scoria) which allows moisture to spread under the slab. *The block has to be perfectly flat usually causing drainage issues especially in highly reactive sites. *You don't get to check if the soil test results are correct as there is no excavation.Soft spots, tree roots and obstructions are never exposed during trench excavations. *"E" reactive sites are often called "H2" because once it is an "E" you can't use a waffle.If you constantly call sites "E" you will lose volume builders because they only want waffles.You may say well to bad the site is what it is and I agree with this but the fact is it influences what geotech's are prepared to say so waffles are put on "E" sites. You can build E waffle, no law says you can't. It just must be engineered, extra concrete, extra steel, piers etc and the usual drainage requirements. All this anecdotal talk is fun but where is the long term scientific evidence? We all know the waffle slab disaster of the late noughties when the longest drought in Victorian history broke etc and all the waffle pods heaved and Metricon getting sued etc, but that all coincided with Metricon becoming the biggest project builder in Australia, so of course they had the biggest exposure. Plus they were building on poorly classified land, which hadn't been tested thoroughly enough. Since then the standards have been upgraded to find a compromise that suits builders and engineers. Let's see the results of a proper scientific survey before we try and scare people eh? It's a heavy read but explains almost everything that happened with the slab heave in Melbourne. New Post-Construction Site Characterisation Models for Low-rise ...https://researchbank.swinburne.edu.au/f ... thesis.pdf Re: Which Slab is Better? Waffle Pod or Raft Concrete Slab?? 40Feb 06, 2019 7:44 pm alexp79 I don't believe proper scientific research is something which can be done here, what will be study protocol and methodology like? And how much it will cost? I would say that if building-expert, who have inspected 1000s of houses, says that waffles on clay tend to me much riskier to heave and require more maintenance, then it is likely to be so. It also pretty well aligns with the theory - waffles have much higher odds of getting heave due to bad drainage or maintenance due to the fact that it is much easier for the water to get under slab. The Soil classification has little to do with piers. The purpose of the classing of the soil is to identify the clay content and the "average expected range of movement… 2 9854 brokers will also be in a position to get you a better rate than the advertised rate most times. 6 7575 That's a bit of a vague question. Either cupboard size is fine. 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