Browse Forums Building A New House 1 Jul 10, 2019 8:14 pm I am building a house with a volume builder where fixed site cost covers all slab types(M, H1, H2, P) up to P class. Now my soil test arrived with classifying the soil as H2 class, although the builder is going to give us H1 slab as per engineering plans. My knowledge of slabs is limited. What is the difference between H1 and H2 class slabs? Can you please guide me whether I should go ahead with H1 as recommended by the builder or push the builder for H2 class slab instead? Re: H1 slab for H2 class soil 2Jul 10, 2019 9:07 pm parthiv777 I am building a house with a volume builder where fixed site cost covers all slab types(M, H1, H2, P) up to P class. Now my soil test arrived with classifying the soil as H2 class, although the builder is going to give us H1 slab as per engineering plans. My knowledge of slabs is limited. What is the difference between H1 and H2 class slabs? Can you please guide me whether I should go ahead with H1 as recommended by the builder or push the builder for H2 class slab instead? H2 classification indicates more reactive clay than H1 (to simplify things, it will cost you more money to have a slab which performs the same under H2 conditions compared to H1 conditions). The engineer should be designing the slab and foundations based on the site classification in the soil report, so H2 in your case. That assumes that you and the engineer are looking at the same report - is that the case? Re: H1 slab for H2 class soil 3Jul 10, 2019 9:26 pm iTool parthiv777 I am building a house with a volume builder where fixed site cost covers all slab types(M, H1, H2, P) up to P class. Now my soil test arrived with classifying the soil as H2 class, although the builder is going to give us H1 slab as per engineering plans. My knowledge of slabs is limited. What is the difference between H1 and H2 class slabs? Can you please guide me whether I should go ahead with H1 as recommended by the builder or push the builder for H2 class slab instead? H2 classification indicates more reactive clay than H1 (to simplify things, it will cost you more money to have a slab which performs the same under H2 conditions compared to H1 conditions). The engineer should be designing the slab and foundations based on the site classification in the soil report, so H2 in your case. That assumes that you and the engineer are looking at the same report - is that the case? Yes, they did prepare the engineering report from the same soil report. Re: H1 slab for H2 class soil 4Jul 11, 2019 8:14 am We do quite a few waffle pod slabs ranging from H1 to H2. There is a difference between the thickness of the concrete used. A H1 slab uses a 300mm pod with 85mm thick concrete above. A H2 slab uses a 300mm pod with 100mm thick concrete above. Are you able to request to view the engineering plans and even contact the engineer yourself? One thing I would be weary of is if the builder is only allowing a H1 slab in the contract they may try and issue you a variation for the upgrade to the H2 (the cost would be at their discretion). Keep us updated and hope this helps! Re: H1 slab for H2 class soil 5Jul 11, 2019 3:44 pm It is NEVER a good idea to have waffle slab for either H1 or H2 soil. Generally, it is not a good idea to have a waffle slab on any soil at all (as it is just a mockery of a foundation), but especially on a highly reactive soil it is a pretty much a recipe for trouble (as it is almost impossible to provide a good drainage). Re: H1 slab for H2 class soil 7Jul 11, 2019 9:08 pm Ardo Ye ole school raft slabs perform just as bad as a waffle pod slab. It's the workmanship and follow up lack of moisture control that destroys foundations. Re: H1 slab for H2 class soil 8Jul 11, 2019 9:51 pm These days all builders apart from Henley builds on Waffle slab in Melbourne’s west(mostly H2 soil), i asked my builder about raft slab upgrade, quote came around 10k. That’s why i might try to ask quote for H2 upgrade. Re: H1 slab for H2 class soil 9Jul 12, 2019 9:38 am l_vanslyke We do quite a few waffle pod slabs ranging from H1 to H2. There is a difference between the thickness of the concrete used. A H1 slab uses a 300mm pod with 85mm thick concrete above. A H2 slab uses a 300mm pod with 100mm thick concrete above. Are you able to request to view the engineering plans and even contact the engineer yourself? One thing I would be weary of is if the builder is only allowing a H1 slab in the contract they may try and issue you a variation for the upgrade to the H2 (the cost would be at their discretion). Keep us updated and hope this helps! I have requested them to send me the engineering plans asap. Re: H1 slab for H2 class soil 10Jul 12, 2019 12:04 pm alexp79 It is NEVER a good idea to have waffle slab for either H1 or H2 soil. Generally, it is not a good idea to have a waffle slab on any soil at all (as it is just a mockery of a foundation), but especially on a highly reactive soil it is a pretty much a recipe for trouble (as it is almost impossible to provide a good drainage). How about you elaborate with factual evidence instead of scaremongering. I'd be really interested to hear how you think drainage differs (cause and effect) between a raft and waffle pod slab designed for a H2 soil classification. Let's assume they are designed by competent engineers, build by competent tradespeople and maintained correctly. Waffle pod slabs are a perfectly acceptable solution for any soil type, If they weren't they would not be listed as an acceptable solution in the Australian Standards AS2870. Re: H1 slab for H2 class soil 11Jul 12, 2019 3:06 pm l_vanslyke alexp79 It is NEVER a good idea to have waffle slab for either H1 or H2 soil. Generally, it is not a good idea to have a waffle slab on any soil at all (as it is just a mockery of a foundation), but especially on a highly reactive soil it is a pretty much a recipe for trouble (as it is almost impossible to provide a good drainage). How about you elaborate with factual evidence instead of scaremongering. I'd be really interested to hear how you think drainage differs (cause and effect) between a raft and waffle pod slab designed for a H2 soil classification. Let's assume they are designed by competent engineers, build by competent tradespeople and maintained correctly. Waffle pod slabs are a perfectly acceptable solution for any soil type, If they weren't they would not be listed as an acceptable solution in the Australian Standards AS2870. https://www.cornellengineers.com.au/beware-waffle-slabs/ https://www.vba.vic.gov.au/__data/assets/pdf_file/0010/20107/Slab-heave-research.pdf "Waffle slabs are not recommended on highly reactive clay sites (Class H1 and H2) because the requirements for good drainage are almost impossible to achieve." Just evaluate the odds of getting competent engineers, tradespeople and future owners maintaining property per guidelines and you would realise that it is always better to be safe than sorry. Opal Towers as well as many thousands of problematic slab heaving houses at Victoria were notably built to Australian Standards and by "competent" tradespeople too. Australian Building Standards are outdated and long overdue to be revised. Unfortunately, they are not taking into consideration the degrading quality of builders and trading people on the actual jobs (as well as a growing number of incompetent engineers too), hence, more safeguards will be needed. Re: H1 slab for H2 class soil 12Jul 12, 2019 4:03 pm alexp79 l_vanslyke alexp79 It is NEVER a good idea to have waffle slab for either H1 or H2 soil. Generally, it is not a good idea to have a waffle slab on any soil at all (as it is just a mockery of a foundation), but especially on a highly reactive soil it is a pretty much a recipe for trouble (as it is almost impossible to provide a good drainage). How about you elaborate with factual evidence instead of scaremongering. I'd be really interested to hear how you think drainage differs (cause and effect) between a raft and waffle pod slab designed for a H2 soil classification. Let's assume they are designed by competent engineers, build by competent tradespeople and maintained correctly. Waffle pod slabs are a perfectly acceptable solution for any soil type, If they weren't they would not be listed as an acceptable solution in the Australian Standards AS2870. https://www.cornellengineers.com.au/beware-waffle-slabs/ https://www.vba.vic.gov.au/__data/assets/pdf_file/0010/20107/Slab-heave-research.pdf "Waffle slabs are not recommended on highly reactive clay sites (Class H1 and H2) because the requirements for good drainage are almost impossible to achieve." Just evaluate the odds of getting competent engineers, tradespeople and future owners maintaining property per guidelines and you would realise that it is always better to be safe than sorry. Opal Towers as well as many thousands of problematic slab heaving houses at Victoria were notably built to Australian Standards and by "competent" tradespeople too. Australian Building Standards are outdated and long overdue to be revised. Unfortunately, they are not taking into consideration the degrading quality of builders and trading people on the actual jobs (as well as a growing number of incompetent engineers too), hence, more safeguards will be needed. Re: H1 slab for H2 class soil 13Jul 12, 2019 4:32 pm alexp79 l_vanslyke alexp79 It is NEVER a good idea to have waffle slab for either H1 or H2 soil. Generally, it is not a good idea to have a waffle slab on any soil at all (as it is just a mockery of a foundation), but especially on a highly reactive soil it is a pretty much a recipe for trouble (as it is almost impossible to provide a good drainage). How about you elaborate with factual evidence instead of scaremongering. I'd be really interested to hear how you think drainage differs (cause and effect) between a raft and waffle pod slab designed for a H2 soil classification. Let's assume they are designed by competent engineers, build by competent tradespeople and maintained correctly. Waffle pod slabs are a perfectly acceptable solution for any soil type, If they weren't they would not be listed as an acceptable solution in the Australian Standards AS2870. https://www.cornellengineers.com.au/beware-waffle-slabs/ https://www.vba.vic.gov.au/__data/assets/pdf_file/0010/20107/Slab-heave-research.pdf "Waffle slabs are not recommended on highly reactive clay sites (Class H1 and H2) because the requirements for good drainage are almost impossible to achieve." Just evaluate the odds of getting competent engineers, tradespeople and future owners maintaining property per guidelines and you would realise that it is always better to be safe than sorry. Opal Towers as well as many thousands of problematic slab heaving houses at Victoria were notably built to Australian Standards and by "competent" tradespeople too. Australian Building Standards are outdated and long overdue to be revised. Unfortunately, they are not taking into consideration the degrading quality of builders and trading people on the actual jobs (as well as a growing number of incompetent engineers too), hence, more safeguards will be needed. I was afraid you would reference that engineer, first thing that pops up with a google search. I'd hardly be taking advice on waffle pod systems from a consultant that has never even designed one before. In reference to the VBA Slab Heaving Research, this is a great point and I'm glad you brought it up! The document in no way states waffle pods as the cause to the issue of slab heaving. It even goes as far to say "appropriate engineering design processes were followed, geotechnical investigation was done properly, and, floor slab designs met the regulatory process" . It states potential problems were caused by inadequate and incorrect drainage at sites that have been classified as reactive (being H1, H2 & E). Again none of this is specific to waffle pod systems as raft slabs are just as susceptible to inadequate and incorrect drainage causing slab heave. The VBA made several recommendations in regards to stormwater management and slab & footing maintenance by the owners. They did not make recommendations to avoid waffle pod systems. The odds of getting competent engineers and tradespeople is actually very likely. We have been using both waffle and raft slab systems for decades on a range of sites from A to E with no issues. I disagree that the standards are outdated. The issue I see is more so with the private certification process but that's a whole other story! Re: H1 slab for H2 class soil 14Jul 12, 2019 8:13 pm 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. *The block has to be cut 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. *No "dug in" edge beam to restrict moisture ingress under the slab. Re: H1 slab for H2 class soil 15Jul 13, 2019 12:40 am Well, ask experts on this forum. I would rather refer to buildinginspector experience, who have inspected tens of thousands of home. Insider above is also an expert on foundations. Cornell Engineers is not the last engineering firm in this country too, when it gets to residential structural engineering. Re: H1 slab for H2 class soil 16Jul 13, 2019 12:44 am l_vanslyke I was afraid you would reference that engineer, first thing that pops up with a google search. I'd hardly be taking advice on waffle pod systems from a consultant that has never even designed one before. In reference to the VBA Slab Heaving Research, this is a great point and I'm glad you brought it up! The document in no way states waffle pods as the cause to the issue of slab heaving. It even goes as far to say "appropriate engineering design processes were followed, geotechnical investigation was done properly, and, floor slab designs met the regulatory process" . It states potential problems were caused by inadequate and incorrect drainage at sites that have been classified as reactive (being H1, H2 & E). Again none of this is specific to waffle pod systems as raft slabs are just as susceptible to inadequate and incorrect drainage causing slab heave. The VBA made several recommendations in regards to stormwater management and slab & footing maintenance by the owners. They did not make recommendations to avoid waffle pod systems. The odds of getting competent engineers and tradespeople is actually very likely. We have been using both waffle and raft slab systems for decades on a range of sites from A to E with no issues. I disagree that the standards are outdated. The issue I see is more so with the private certification process but that's a whole other story! Interesting, how you still do waffles on E sites "for decades" as it is pretty much prohibited Also interested to hear how do you generally handle/resolve drainage problems on reactive sites during the construction, too. Re: H1 slab for H2 class soil 17Jul 13, 2019 7:28 am alexp79 l_vanslyke I was afraid you would reference that engineer, first thing that pops up with a google search. I'd hardly be taking advice on waffle pod systems from a consultant that has never even designed one before. In reference to the VBA Slab Heaving Research, this is a great point and I'm glad you brought it up! The document in no way states waffle pods as the cause to the issue of slab heaving. It even goes as far to say "appropriate engineering design processes were followed, geotechnical investigation was done properly, and, floor slab designs met the regulatory process" . It states potential problems were caused by inadequate and incorrect drainage at sites that have been classified as reactive (being H1, H2 & E). Again none of this is specific to waffle pod systems as raft slabs are just as susceptible to inadequate and incorrect drainage causing slab heave. The VBA made several recommendations in regards to stormwater management and slab & footing maintenance by the owners. They did not make recommendations to avoid waffle pod systems. The odds of getting competent engineers and tradespeople is actually very likely. We have been using both waffle and raft slab systems for decades on a range of sites from A to E with no issues. I disagree that the standards are outdated. The issue I see is more so with the private certification process but that's a whole other story! Interesting, how you still do waffles on E sites "for decades" as it is pretty much prohibited Also interested to hear how do you generally handle/resolve drainage problems on reactive sites during the construction, too. I didn’t say that at all, as I said above “we have been using both waffle and raft slab systems for decades on a range of sites from A to E” Drainage issues can be aided by the following: - ensuring when the site cut is done, soil falls away from the slab - using a granular base or bedding sand - engineer designed and located field gullies (this is an integral part of the slab design) Re: H1 slab for H2 class soil 18Jul 13, 2019 8:12 am 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 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 13098 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 9853 I don’t think so as the floor area over 300 square meters then it is class 3…. 12 17936 |