Hi guys,
Today my builder told me that our slab needs to be upgraded from P class to E class which will costs about 8K.
We have fixed site cost on the contract and it covers slab upgrade upto class P.
we thought P class slab would cost the most as it is the bottom of the list of soil classfication on internet. So, we did not expect to pay more on the site cost but we probably need to pay more.
Is it true that class E slab costs higher than class P? I couldn't find anywhere in internet on the price comparison between class E and class P slab.
Thank you for your answer in advance.
Regards,
Peter
Builder asked to upgrade class P to E class slab
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Cloudcoach
Ask for a copy of the geotech report and Engineering
then check AS2870 Residential Slabs & Footings
If anomalies appear it pays to get your own engineer,etc,etc
Ask for a copy of the geotech report and Engineering
then check AS2870 Residential Slabs & Footings
If anomalies appear it pays to get your own engineer,etc,etc
P doesn’t mean anything. It just means there’s something ‘special’ about the site such as a KDR or large trees etc. there should be another rating for the underlying soil (S, M, H etc). The slab engineer will look at all the factors including the reasons why it’s classified P and the underlying soil condition.
I always "enjoy" when a builder states they need to "upgrade" from a Class "X" to a Class "Z", as they should actually be saying we need to downgrade your class.
Class E means an "Extreme" reactivity for the clays to move with changes in soil moisture content i.e. when clays wet up or gain moisture they swell/expand and when clays dry out they shrink/settle.
I assume you are in QLD where E Class soils are prominent especially in western Brisbane and also in parts of the northern suburbs.
The difference in a Class P and Class E is irrelevant as kirashogun mentioned above as the Class E is a differential movement (i.e. structural stiffness) reference and the Class P is a "Problem" site according to AS2870.
And yes you can have a Class P site with "problems" i.e. trees, uncontrolled fill etc and still require a Class E type slab i.e. Class E structural stiffness.
This is why a good geotechnical firm will always classify the;
1. Reactivity of the site Class, A, S M, H1, H2 or E
2. the "Site Classification" in terms with Section 1 of AS2870 i.e. Class P because of (trees, fill, etc) with soil reactiviity in "normal" circumstances within the Class A, S, M, N1, H2 or E range.
Site Classification is exactly that. You gain a reactivity to moisture change (A, S, M, H1, H2 or E) and then apply it to the site. Where "problem" sites occur its called Class P.
Hope this helps.
Class E means an "Extreme" reactivity for the clays to move with changes in soil moisture content i.e. when clays wet up or gain moisture they swell/expand and when clays dry out they shrink/settle.
I assume you are in QLD where E Class soils are prominent especially in western Brisbane and also in parts of the northern suburbs.
The difference in a Class P and Class E is irrelevant as kirashogun mentioned above as the Class E is a differential movement (i.e. structural stiffness) reference and the Class P is a "Problem" site according to AS2870.
And yes you can have a Class P site with "problems" i.e. trees, uncontrolled fill etc and still require a Class E type slab i.e. Class E structural stiffness.
This is why a good geotechnical firm will always classify the;
1. Reactivity of the site Class, A, S M, H1, H2 or E
2. the "Site Classification" in terms with Section 1 of AS2870 i.e. Class P because of (trees, fill, etc) with soil reactiviity in "normal" circumstances within the Class A, S, M, N1, H2 or E range.
Site Classification is exactly that. You gain a reactivity to moisture change (A, S, M, H1, H2 or E) and then apply it to the site. Where "problem" sites occur its called Class P.
Hope this helps.
Hi all,
Thanks for taking time to answer. I really appreciate it.
At the moment I signed that I will pay for the variation because my builder insisted that they are right and I cannot convince them.
Below 4 screenshots are my tender item 5, 11, 19 and 23. It does not look so clear what slab is included. All 4 items were in the tender by default. My builder told me the site cost will be fixed, but I didn't believe so I asked them to add slab upgrade to p which is on the note on the item 19.
One thing I found just now is there is no piers mentioned in my tender. I am not sure if piers are included in any type of slap by default. So, if they charged 8K for piers, then I think it makes sense although I don't know how much it actually cost. There are around 35 piers in the engineering plan.
If my builder said that they need to charge more because the additional piers, then I wouldn't doubt too much.
Thank you again everyone.
Thanks for taking time to answer. I really appreciate it.
At the moment I signed that I will pay for the variation because my builder insisted that they are right and I cannot convince them.
Below 4 screenshots are my tender item 5, 11, 19 and 23. It does not look so clear what slab is included. All 4 items were in the tender by default. My builder told me the site cost will be fixed, but I didn't believe so I asked them to add slab upgrade to p which is on the note on the item 19.
One thing I found just now is there is no piers mentioned in my tender. I am not sure if piers are included in any type of slap by default. So, if they charged 8K for piers, then I think it makes sense although I don't know how much it actually cost. There are around 35 piers in the engineering plan.
If my builder said that they need to charge more because the additional piers, then I wouldn't doubt too much.
Thank you again everyone.
If you don't mind who is your builder? We had same issue with our build!
If you don't mind who is your builder? We had same issue with our build!
We are building with Bentley homes. I guess they are only building in Melbourne. Hope your builder didn't charge you too much.
If you don't mind who is your builder? We had same issue with our build!
We are building with Bentley homes. I guess they are only building in Melbourne. Hope your builder didn't charge you too much.
We also paid 8k ☹
Did they supply you with engineering drawings? My builder supplied the engineering drawings which showed exactly how the slab and frame is designed, where steel beams should go and thickness of members etc. All this should be supplied BEFORE signing your HIA contract so you know exactly what you are paying for.
Similar situation up here in Ipswich. charged 15k to upgrade slab (slab upgraded from M to E2) and another 15k for bored piers (1m min depth) (P class site because of trees of influence).
Strange thing is that the mining report says that the area is known for H to H2 soils?
Strange thing is that the mining report says that the area is known for H to H2 soils?
Hi Diggi,
Firstly, I have quickly reviewed your classification of which you have kindly scanned and provided. I do know the company you have engaged as I know there lay out and they are one of my main competetors. However based on their results and your shrink/swell results (laboratory test results), of 6.09% and 4.47% combined with an Ipswich Hs zone of 2300mm, I would 100% concurr with the E Classification.
Q1: are these costs reasonable for a double story house?
I will not comment on your questions about costings due to your classification because this will generally be builder specific based on costs, subcontractor costs, mark ups etc.
Q2: is there anyway to improve on the P class by removing root balls and filling with Crusher dust (bearing in mind large tree 5m away)
Unfortunately a large tree being 4-5metres away from your proposed footprint is of serious concern and therefore this one tree on a Class "E" site being zone of influence of 2.0 times mature height will most likely end up in your entire footprint being piered. In passing comment I would probably predict that the piers will be much deeper then 1metre, possibly 2metres or 2.5metres within the zone.
Q3:does the Geotech hole look normal as it seems very shallow (do they normally fill cored hole back in?) see photos (hopefully i can get them to download)
Yes this does look standard and yes they do backfill the borehole. Legally, if you walked on site and fell and broke your ankle in a borehole then there would be issues.
Q4"Builder only covers M class (of course... even though we are in South East Queensland:-?)"
- This is standard and unfortunately being in Ipswich yes you have a higher percentage of going above Class M, but the same percentage of clients on the coast line having a Class M. As builders move further west in developments well there is a good argument that builders should start offering higher Classes (H1, H2) as standard.
Q5 "and intend to remove all root balls and fill with crusher dust"
You will be effectively be creating a large hole filled with a material that is more permeable then the soil around it. i.e. you will be creating a mini dam. Simple terms you have concrete as soil. You dig the concrete out and replace it with soil. When it rains the water gets into the soil but cannot (only slowly) penetrate the concrete. You would be far better off, backfilling and compacting with a clay based soil which has a lower reactivity then the soil around it. This is the reason why the plumbing code AS3500 requires plumbing trenches where they enter and exit the slab to be "plugged" with a clay plug or betonite. Rather then backfilled with "crusher dust".
Hope this helps;
Geo1
Firstly, I have quickly reviewed your classification of which you have kindly scanned and provided. I do know the company you have engaged as I know there lay out and they are one of my main competetors. However based on their results and your shrink/swell results (laboratory test results), of 6.09% and 4.47% combined with an Ipswich Hs zone of 2300mm, I would 100% concurr with the E Classification.
Q1: are these costs reasonable for a double story house?
I will not comment on your questions about costings due to your classification because this will generally be builder specific based on costs, subcontractor costs, mark ups etc.
Q2: is there anyway to improve on the P class by removing root balls and filling with Crusher dust (bearing in mind large tree 5m away)
Unfortunately a large tree being 4-5metres away from your proposed footprint is of serious concern and therefore this one tree on a Class "E" site being zone of influence of 2.0 times mature height will most likely end up in your entire footprint being piered. In passing comment I would probably predict that the piers will be much deeper then 1metre, possibly 2metres or 2.5metres within the zone.
Q3:does the Geotech hole look normal as it seems very shallow (do they normally fill cored hole back in?) see photos (hopefully i can get them to download)
Yes this does look standard and yes they do backfill the borehole. Legally, if you walked on site and fell and broke your ankle in a borehole then there would be issues.
Q4"Builder only covers M class (of course... even though we are in South East Queensland:-?)"
- This is standard and unfortunately being in Ipswich yes you have a higher percentage of going above Class M, but the same percentage of clients on the coast line having a Class M. As builders move further west in developments well there is a good argument that builders should start offering higher Classes (H1, H2) as standard.
Q5 "and intend to remove all root balls and fill with crusher dust"
You will be effectively be creating a large hole filled with a material that is more permeable then the soil around it. i.e. you will be creating a mini dam. Simple terms you have concrete as soil. You dig the concrete out and replace it with soil. When it rains the water gets into the soil but cannot (only slowly) penetrate the concrete. You would be far better off, backfilling and compacting with a clay based soil which has a lower reactivity then the soil around it. This is the reason why the plumbing code AS3500 requires plumbing trenches where they enter and exit the slab to be "plugged" with a clay plug or betonite. Rather then backfilled with "crusher dust".
Hope this helps;
Geo1
In my build the original footings were to be a minimum 800 mm deep all round. The original report also mentioned that no footings should be located within 75% of the mature height of any nearby tree. Since there were three saplings recently planted by the developer on the nature strip, my block earned a P rating.
When I enquired with the council as to what type of trees they were and how high they were expected to grow, I realised that eventually a couple of parts of the dwelling would come within 75% of their mature height (which is around 12 metres).
The engineer then re-specified a number of piers - 7 in all - which now go down to 2.5 metres. These are the piers that are within that "75%" influence zone.
I actually found it interesting that my slab has a very large number of piers. The house I built 20 years ago just had one. This house has 22 of them - and it is a tiny house (only around 130 m2) sitting on M-D soil. That said, I actually asked them to upgrade the slab two "half classes" above what the soil report demanded, even though it obviously cost me more money. So I asked for the engineer to design an H1-D slab. I personally feel that the current Australian standards for residential construction are not necessarily ideal and instead are a compromise between mitigating the liklihood of problems occurring down the track versus what people are prepared to pay.
Perhaps some will say I am being overzealous but the cost difference wasn't that large and if it reduces the chance of doors sticking or other issues years down the track I think it is a small price to pay here and now. Anyway, if any builder said to me they wanted to upgrade the footings or slab, I would not hesitate to agree to this.
When I enquired with the council as to what type of trees they were and how high they were expected to grow, I realised that eventually a couple of parts of the dwelling would come within 75% of their mature height (which is around 12 metres).
The engineer then re-specified a number of piers - 7 in all - which now go down to 2.5 metres. These are the piers that are within that "75%" influence zone.
I actually found it interesting that my slab has a very large number of piers. The house I built 20 years ago just had one. This house has 22 of them - and it is a tiny house (only around 130 m2) sitting on M-D soil. That said, I actually asked them to upgrade the slab two "half classes" above what the soil report demanded, even though it obviously cost me more money. So I asked for the engineer to design an H1-D slab. I personally feel that the current Australian standards for residential construction are not necessarily ideal and instead are a compromise between mitigating the liklihood of problems occurring down the track versus what people are prepared to pay.
Perhaps some will say I am being overzealous but the cost difference wasn't that large and if it reduces the chance of doors sticking or other issues years down the track I think it is a small price to pay here and now. Anyway, if any builder said to me they wanted to upgrade the footings or slab, I would not hesitate to agree to this.
Thanks Geo1, I think I will just have to learn my lesson from this one.
next time, get soil test done before buying land, me thinks.
next time, get soil test done before buying land, me thinks.
Often with new land releases soil tests are included if you ask (albeit commissioned by the vendor / developer). If you are working to buy the land with a builder who has done other houses in the neighbourhood you can at least get an indication upfront of the typical conditions they have previously encountered. Sometimes the builder will give you the contact details of their geotechnical engineers. That is what happened in my case and they were more than happy to spend 15 minutes on the phone with me (it helped that the same company also does the footing and slab engineering).
When I bought my land I considered getting a soil test but then I realised what was the point. The cost is what it is and getting the land in the right location was more than hard enough. Getting land in the right location and with a "perfect" soil test almost impossible.
When I bought my land I considered getting a soil test but then I realised what was the point. The cost is what it is and getting the land in the right location was more than hard enough. Getting land in the right location and with a "perfect" soil test almost impossible.
Thanks Geo1, I think I will just have to learn my lesson from this one.
next time, get soil test done before buying land, me thinks.
next time, get soil test done before buying land, me thinks.
Diggi,
I always get upset when people need to learn lessons when it costs money. If it didn't cost money would we learn?
Unfortunately its the human way.
We spend $400-$600 for a building and pest inspection of an existing dwelling of which are generally just recommendations and lots and lots of terms and conditions. But we do not spend $400-$600 on a soil test prior to purchasing a block of land.
When you think about it, a builder (in general) are very good at understanding their costs above ground, i.e. They know how much the painter will cost per metre, they generally are very good at estimating the amount of 4x2's in the frame etc. They only thing they do not know, hence the requirement for your deposit is to undertake a site survey and borehole report. Site survey because every site will generally have a different slope and therefore different cost in earthworks. Borehole report, because every site will have a different engineering design of the slab from the report and therefore different costs with reo, concrete etc. Standard designs and standard inclusions are just that, the builder has costed those to the 0.1c and therefore they know they can make money off them. When you look at any building contracts the variations and therefore costs come from changes to the standard designs and inclusions, earthworks and slab upgrades.
Makes sense to get a contour survey done and borehole report done as a term in any contract purchasing new land. These two things will be your biggest unknown. Yes every builder will have their different variations above ground but generally you can nut the ones out that are just ripping off for a power point or tiles instead of carpet etc.
Regards
Geo1
Agreed, the least they can do is make the slab upgrade details/costs transparent, and maybe, only a small % markup.
Tried getting the details of the $15k piles and $15k slab upgrade from builder... doesnt look like they have a policy that allows this.
I mentioned that most contracts have % markup for Variations on subbie costs, to which they replied that this is not a variation as the final contract has not been signed, therefore this is merely a quote. (to which i replied AAAHA, thats how you do it!)
Still, ill keep trying.
Tried getting the details of the $15k piles and $15k slab upgrade from builder... doesnt look like they have a policy that allows this.
I mentioned that most contracts have % markup for Variations on subbie costs, to which they replied that this is not a variation as the final contract has not been signed, therefore this is merely a quote. (to which i replied AAAHA, thats how you do it!)
Still, ill keep trying.
Are there any concreters out there that have done an E slab ("P site" needing with 1-2m piers because of a tree) lately.
For an average size double story house)
see
viewtopic.php?p=1810898#p1810898
For an average size double story house)
see
viewtopic.php?p=1810898#p1810898
Did they supply you with engineering drawings? My builder supplied the engineering drawings which showed exactly how the slab and frame is designed, where steel beams should go and thickness of members etc. All this should be supplied BEFORE signing your HIA contract so you know exactly what you are paying for.
Hi. Kirashogun
Could you pm me what your slab engineering drawings look like i know we did not get anything it would great to see what they really look like.
Thank you
Mario.
Related
15/08/2023
9
Well thats a relief! The whole family is sick of waiting.
15/12/2023
2
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…