Browse Forums Building A New House Re: H1 slab for H2 class soil 19Jul 13, 2019 1:12 pm l_vanslyke insider Several problems with the waffle that you don't get with Raft slabs *Granular bedding material (used to be scoria) which allows moisture to spread under the slab. Same can be done for waffle pod systems. Good practice to use nominal 50mm bedding. *The block has to be cut perfectly flat usually causing drainage issues especially in highly reactive sites. Soil should always fall away from the slab, if the building pad needs to be raised to achieve this then so be it. Engineers specify this as a requirement as part of the design and the builder needs to ensure this happens. *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. Waffle pod systems also utilise footings, edge beams and drilled piers, a perfect chance to confirm the soil test is accurate. If tree roots are encountered during the soil test the site would be reclassified as P which is also taken into account when the engineer specifies their Design Range. Quote: *"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. I find it hard to believe that an engineering firm would do this, not worth risking their licence and credibility. However I've seen some stranger things happen in the building industry. *No "dug in" edge beam to restrict moisture ingress under the slab. Agree Job and use everything you are supposed to and do the right thing,what insider and Cornell say is that unless basically everything is done absolutely correct and conditions are not too dire, waffle slabs have no place in our building world where errors and short cuts are so common, unfortunately you are the acception in a very non compliant industry. Re: H1 slab for H2 class soil 20Jul 14, 2019 9:49 pm “Same can be done for waffle pod systems. Good practice to use nominal 50mm bedding.” Thats my point the granular layer under the waffle allows moisture ingress undrer the slab but that is not the situation with the convential raft slab. “Soil should always fall away from the slab, if the building pad needs to be raised to achieve this then so be it. Engineers specify this as a requirement as part of the design and the builder needs to ensure this happens.” Unfortunately builders don’t slope the ground away from the house. You can see this fact at any new housing estate.I would like to see anybody post halve a dozen examples of a properly drained house underconstruction to AS2870 standards. “Waffle pod systems also utilise footings, edge beams and drilled piers, a perfect chance to confirm the soil test is accurate. If tree roots are encountered during the soil test the site would be reclassified as P which is also taken into account when the engineer specifies their Design Range.” The majority of waffle slabs don’t have piers or deepened edge beams so that doesn’t apply in most cases. *"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. “I find it hard to believe that an engineering firm would do this, not worth risking their licence and credibility. However I've seen some stranger things happen in the building industry. “ I know this for a fact and it is a major problem in the industry The biggest problem with waffles is site prepartion.Cut flat, granular bedding, no temporary downpipes and artificial slopes built up against the slab. Everything has to be done correctly with waffles and unfortuntely with no enforcment of the standards this isn’t happening. I would built with a waffle only on class “M” or less soil reativity. With the recent rain we may see further slab heave cases occuring but maybe not the same magnitude as the previous two slab heave waves. I am not sure whether Perth has its own way of doing things in regards to this. Most of Perth has class A (sandy soil), except for some areas near rivers or hills. 2 13107 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 9863 I don’t think so as the floor area over 300 square meters then it is class 3…. 12 17943 |