Browse Forums Building A New House 1 Nov 22, 2014 11:02 am Please help seeking assistance regarding the slab designed for a house that we are building in Melbourne North West. I signed a contract with fixed site cost to build single story house with one of the volume builders before soil test was carried out. The same builder has built our next door neighbour's house last year and their site cost was almost identical. The only difference their one had piers (apparently because of easement) and ours doesn’t. When our soil test was done the result were as follows Hole 1(mm) 0 - 500 Hole 2(mm) 0 - 400 Hole 3(mm) 0 - 400 CONTROLFILL--FILL – SILTY CLAY - damp, mottled dark brown grey orange,moderately compacted, firm, root material, gravely pockets Hole 1(mm) 500 - 900 Hole 2(mm) 400 - 900 Hole 3(mm) 400 -800 A SILTY CLAY (CH) – damp, mottled dark brown grey orange to mottled light brown grey orange, stiff, high plasticity, root material, calcareous pockets, basaltic rock pockets. REFUSAL ON BASALTIC BOULDERS IN ALL BOREHOLES The boreholes on this site revealed that basalt rock was encountered at shallow depths. The site was classified P because of a fill however after the compaction report it was reclassified “H2”. Before the fill the natural soils was classed as“H2” site classification. Based on the soil test they recommended “”Particular care should be taken to provide adequate articulation given the reactivity of the natural clays and potential for moisture content changes in the FILL soils and natural clays. in some instances allow for additional stiffness in the slab to accommodate any potential abnormal moisture conditions that may develop after construction. Furthermore, movement tolerant plumbing connections must be provided. As an alternative to a raft slab foundation arrangement, deeper footing construction, such as bored piers or deepened edge and internal beams, could be considered with the minimum requirements for a “Class H2”.”” Then the same engineering company designed a waffle pod slab with out piers Overall Slab depth - 385 mm Void form height – 300mm Slab thickness -85mm Internal Rib width -110mm External Rib width 300mm Stem width- 150mm Slab reinforcement Top Slab fabric - SL92 External Rib -3-L1TM Bottom Internal Rib 1-N16 External Rib 3-N16 or 2x3-L1TM To those who are knowledgeable please help if you know the slab designed is actually appropriate for the block we have. I am just worried because of the inconsistency between the recommendation on the soil report (raft slab) and the engineering plan (waffle pod without piers). Your help is greatly appreciated. Re: H2 Slab without Piers 2Nov 22, 2014 10:21 pm Hi pathmhome, I suggest you ask them (always in writing) for a guarantee that they have made all possible efforts to be certain that no heave will occur. There may have been large trees on or near the site within the last 7 years that may cause heave. You stated that there was root material discovered. I'd be asking to go to basalt on my house, but 900mm is not a large depth as regards possible shrinkage it seems to me even though high plasticity was mentioned. Piers will cost though, I warn, Cheers, Leonardo_23 Re: H2 Slab without Piers 3Nov 23, 2014 12:47 am Hi there, Thats interesting that there are no piers on a waffle pod slab. im assuming they only carried out what... 2 boreholes?? thats not enough to conclude that the entire site is a bedrock... and even so, if its a bedroom, piers should be provided until each pier hits the same 'bearing pressure' or each pier hits all bedrock, so that there is consistent movement of the slab with the soil and prevents cracking to dwelling. piers do cost alot... u can allow maybe more or less 4-5k in piers. depending on your builder's rate i suppose. but i think piers shoudl be use to really stabilize the slab. Re: H2 Slab without Piers 4Nov 23, 2014 8:21 am Thank you Leonardo_23 and foot-print Leonard_23 The builder has got 30 year structural guarantee and I have asked the builder about the slab and their response was that "an external engineering company have designed it as per AS 2870." Considering I signed the contract with fixed site cost before the soil test they probably have included the piers in their estimation. I would rather pay for the piers if the structural integrity of the house is going to be enhanced. foot-print They actually did 3 boreholes two of them terminating at 900mm and last one @ 800mm. i am assuming they are not doing the piers because of basaltic rock ?? Re: H2 Slab without Piers 5Nov 23, 2014 8:33 am As first home buyer and builder the whole process has been a steep learning curve. with my limited knowledge i have been researching online. In my understanding the reinforcement and other specification appear in line with AS 2870 standards however there is discrepancy between the recommendation from the soil test and the final engineering plan. I was planning to engage private building inspectors but I found out they only check if the work has been done according to the engineering plan. Apparently they can not check the slab design. What option do I have?? Who should I consult?? Are there any structural engineers?? Re: H2 Slab without Piers 6Nov 23, 2014 10:27 pm Atleast have them guarantee it, in writing, for peace of mind. because even they should know what should be done. and you dont exactly know what "structural guarantee" covers lol. atleast you've backed yourself up ! Re: H2 Slab without Piers 7Apr 30, 2018 10:10 am Hi Pathmhome, I’m having exactly same confusion as you were in 2014. My slab plan shows no piers for a class P/H2 site. May I know how it went with your plan? Did you manage to change the plan to add piers? Or does the builder has any guarantee the slab will work without piers? Thanks, pathmhome Please help seeking assistance regarding the slab designed for a house that we are building in Melbourne North West. I signed a contract with fixed site cost to build single story house with one of the volume builders before soil test was carried out. The same builder has built our next door neighbour's house last year and their site cost was almost identical. The only difference their one had piers (apparently because of easement) and ours doesn’t. When our soil test was done the result were as follows Hole 1(mm) 0 - 500 Hole 2(mm) 0 - 400 Hole 3(mm) 0 - 400 CONTROLFILL--FILL – SILTY CLAY - damp, mottled dark brown grey orange,moderately compacted, firm, root material, gravely pockets Hole 1(mm) 500 - 900 Hole 2(mm) 400 - 900 Hole 3(mm) 400 -800 A SILTY CLAY (CH) – damp, mottled dark brown grey orange to mottled light brown grey orange, stiff, high plasticity, root material, calcareous pockets, basaltic rock pockets. REFUSAL ON BASALTIC BOULDERS IN ALL BOREHOLES The boreholes on this site revealed that basalt rock was encountered at shallow depths. The site was classified P because of a fill however after the compaction report it was reclassified “H2”. Before the fill the natural soils was classed as“H2” site classification. Based on the soil test they recommended “”Particular care should be taken to provide adequate articulation given the reactivity of the natural clays and potential for moisture content changes in the FILL soils and natural clays. in some instances allow for additional stiffness in the slab to accommodate any potential abnormal moisture conditions that may develop after construction. Furthermore, movement tolerant plumbing connections must be provided. As an alternative to a raft slab foundation arrangement, deeper footing construction, such as bored piers or deepened edge and internal beams, could be considered with the minimum requirements for a “Class H2”.”” Then the same engineering company designed a waffle pod slab with out piers Overall Slab depth - 385 mm Void form height – 300mm Slab thickness -85mm Internal Rib width -110mm External Rib width 300mm Stem width- 150mm Slab reinforcement Top Slab fabric - SL92 External Rib -3-L1TM Bottom Internal Rib 1-N16 External Rib 3-N16 or 2x3-L1TM To those who are knowledgeable please help if you know the slab designed is actually appropriate for the block we have. I am just worried because of the inconsistency between the recommendation on the soil report (raft slab) and the engineering plan (waffle pod without piers). Your help is greatly appreciated. Re: H2 Slab without Piers 9May 02, 2018 7:54 am Good point brought up by Leonardo_23 about the trees You should be able to find out about your land before it was subdivided (if it had trees) with historical Google Earth search. 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: H2 Slab without Piers 10Aug 24, 2018 1:15 pm pathmhome Please help seeking assistance regarding the slab designed for a house that we are building in Melbourne North West. I signed a contract with fixed site cost to build single story house with one of the volume builders before soil test was carried out. The same builder has built our next door neighbour's house last year and their site cost was almost identical. The only difference their one had piers (apparently because of easement) and ours doesn’t. When our soil test was done the result were as follows Hole 1(mm) 0 - 500 Hole 2(mm) 0 - 400 Hole 3(mm) 0 - 400 CONTROLFILL--FILL – SILTY CLAY - damp, mottled dark brown grey orange,moderately compacted, firm, root material, gravely pockets Hole 1(mm) 500 - 900 Hole 2(mm) 400 - 900 Hole 3(mm) 400 -800 A SILTY CLAY (CH) – damp, mottled dark brown grey orange to mottled light brown grey orange, stiff, high plasticity, root material, calcareous pockets, basaltic rock pockets. REFUSAL ON BASALTIC BOULDERS IN ALL BOREHOLES The boreholes on this site revealed that basalt rock was encountered at shallow depths. The site was classified P because of a fill however after the compaction report it was reclassified “H2”. Before the fill the natural soils was classed as“H2” site classification. Based on the soil test they recommended “”Particular care should be taken to provide adequate articulation given the reactivity of the natural clays and potential for moisture content changes in the FILL soils and natural clays. in some instances allow for additional stiffness in the slab to accommodate any potential abnormal moisture conditions that may develop after construction. Furthermore, movement tolerant plumbing connections must be provided. As an alternative to a raft slab foundation arrangement, deeper footing construction, such as bored piers or deepened edge and internal beams, could be considered with the minimum requirements for a “Class H2”.”” Then the same engineering company designed a waffle pod slab with out piers Overall Slab depth - 385 mm Void form height – 300mm Slab thickness -85mm Internal Rib width -110mm External Rib width 300mm Stem width- 150mm Slab reinforcement Top Slab fabric - SL92 External Rib -3-L1TM Bottom Internal Rib 1-N16 External Rib 3-N16 or 2x3-L1TM To those who are knowledgeable please help if you know the slab designed is actually appropriate for the block we have. I am just worried because of the inconsistency between the recommendation on the soil report (raft slab) and the engineering plan (waffle pod without piers). Your help is greatly appreciated. I'm in same situation... almost same Slab H2.. Re: H2 Slab without Piers 11Mar 18, 2019 8:37 pm insider You don't have to have piers just because you have a class "P" site.You may have a rigid slab designed by a engineer and is ok to sit in the fill. What is a rigid slab? Is it another name of raft slab? 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 6559 DIY, Home Maintenance & Repair That’s very helpful information. Will find out more from there. Much appreciated. 11 13446 3 1372 |