Browse Forums Building A New House 1 May 03, 2018 12:06 am My block is classified as H2, that is highly reactive clay sites which may experience very high ground movement from moisture changes. However, my builder advised that the soil is a good classification so that the slab needs no piers. Any knowledgeable person could advise me if that is the case? I signed the fixed site cost contract with the builder so I have concern that the builder would like to avoid piering to save cost. Re: Does H2 site classification require slab piers? 2May 03, 2018 6:27 am That H2 is a "good classification" is not true, but that's not a guarantee that piering would be required. I don't have a copy of AS2870 at hand to see if piering is specifically prescribed for H2 sites. My H1 site will have piers due to a designated Tree of Influence, but I suspect it would have required piering regardless of the tree on such soil due to the use of a waffle pod slab. That may not have been the case with a suitably thick raft slab but overall that may still have been more expensive as I understand that waffle pod slabs are quicker to construct. At the end of the day, the best approach would be to engage an independent structural engineer to review the soil report and slab/foundation drawings and provide you with an informed opinion. Unfortunately that advice is not going to be free though... Re: Does H2 site classification require slab piers? 3May 03, 2018 7:12 am larry1124 However, my builder advised that the soil is a good classification so that the slab needs no piers. Based on what, his experience? Why would anyone believe what an unqualified, new home salesman or builder says on engineering matters... ? If you are on a difficult block hire your own independent Engineer, get Soil data and proofs Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Does H2 site classification require slab piers? 4May 04, 2018 9:08 pm Thank you for your advice iTool and StructuralBIMGuy. If anyone else has similar site classification "H1" or "H2", could you share with me how many piers was put into your slab? Thank you. Re: Does H2 site classification require slab piers? 5May 04, 2018 9:34 pm larry1124 If anyone else has similar site classification "H1" or "H2", could you share with me how many piers was put into your slab? To give you some context, I'm looking at ~$10k for a total of 51 piers spread over a 170sq.m footprint. The piers are typically bored at 450mm diameter and need to be founded at minimum depths ranging from 1800mm to 2700mm. Re: Does H2 site classification require slab piers? 6May 05, 2018 9:16 am Do the calcs, concrete is $200/m3 Mini excavator with auger $60/pile Concrete pump $1200 Always check the, volume of the excavated spoil piles, hrs, dimensions & number of concrete trucks.. LOL concrete is often referred to by builders/trades as "Grey Gold " hth Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Does H2 site classification require slab piers? 7May 05, 2018 9:52 am StructuralBIMGuy Do the calcs, concrete is $200/m3 Mini excavator with auger $60/pile Concrete pump $1200 Always check the, volume of the excavated spoil piles, hrs, dimensions & number of concrete trucks.. LOL concrete is often referred to by builders/trades as "Grey Gold " hth Applying those rate estimates and whacking on a 20% builder's margin works out to be only $150 off my variation amount, so a good approximation. Re: Does H2 site classification require slab piers? 8May 15, 2018 8:35 pm The need for piers has no reference to your slab classification i.e. Class, A, M, H1, H2 or E. If your site was classified as Class P, then "in certain instances" you may need piers. The "normal" AS2870 site classification mentioned above (other then Class "P"), are purely a measure of differential movement based on "normal" seasonal moisture variations. i.e Clays when dry will shrink/settle and when wet will swell/expand. You can require piers on any site classification above it will really depend on your site constraints and engineer. By classifying a site as Class H2, the site has been classified as having a "Very High" ability to shrink/swell in changes in soil moisture content. This still does not have anything to do with piers. Piers will only help you in soil shrinkage/subsidence, and the structural stiffness deals with the swell hence you pay for a thicker slab with thicker steel. H2 will require N16's rib bars and edge beam and SL92 mesh. Most QLD builders will reluctantly pier houses unless needed. i.e. Trees within zone of influence, uncontrolled fill, retaining walls, easements, potential pools etc Most NSW builders will pier regardless of understanding mainly because engineers in NSW believe piers solve all problems. Most builders in NSW will construct what they call "construction piers" or 450mm dia 500mm - 1000mm deep regardless of site classification in order to deal with small lots and service pipes running either through the slab or parallel to slab within a short distance. I agree with StructuralBIMGuy above, this is really builders margin 101. You should really be asking the builder "why are the piers required? Is it because of services, easements, fill, bearing pressure etc. Re: Does H2 site classification require slab piers? 9May 15, 2018 10:53 pm Thank you very much for your such detailed explanation, Geo1. It allays my significant concerns on the absence of pier in my H2 slab. Geo1 The need for piers has no reference to your slab classification i.e. Class, A, M, H1, H2 or E. If your site was classified as Class P, then "in certain instances" you may need piers. The "normal" AS2870 site classification mentioned above (other then Class "P"), are purely a measure of differential movement based on "normal" seasonal moisture variations. i.e Clays when dry will shrink/settle and when wet will swell/expand. You can require piers on any site classification above it will really depend on your site constraints and engineer. By classifying a site as Class H2, the site has been classified as having a "Very High" ability to shrink/swell in changes in soil moisture content. This still does not have anything to do with piers. Piers will only help you in soil shrinkage/subsidence, and the structural stiffness deals with the swell hence you pay for a thicker slab with thicker steel. H2 will require N16's rib bars and edge beam and SL92 mesh. Most QLD builders will reluctantly pier houses unless needed. i.e. Trees within zone of influence, uncontrolled fill, retaining walls, easements, potential pools etc Most NSW builders will pier regardless of understanding mainly because engineers in NSW believe piers solve all problems. Most builders in NSW will construct what they call "construction piers" or 450mm dia 500mm - 1000mm deep regardless of site classification in order to deal with small lots and service pipes running either through the slab or parallel to slab within a short distance. I agree with StructuralBIMGuy above, this is really builders margin 101. You should really be asking the builder "why are the piers required? Is it because of services, easements, fill, bearing pressure etc. How good is Simeon?! Always taking time to help others out! Wish we were building in NSW and could work together. Thanks for all that you do! 7 6567 DIY, Home Maintenance & Repair That’s very helpful information. Will find out more from there. Much appreciated. 11 13449 3 1377 |