Browse Forums General Discussion 1 May 16, 2013 10:28 pm I would be very interested if anyone has taken preventative measures and what they were to help relieve the effects of slab heave on their property? Re: Has anyone rectified slab heave successfully 2May 17, 2013 8:50 am Slab heave is caused by water seeping to the soil/clay under the concrete foundations. This happens more so with soil type H and P with a waffle pod slab (styrafome voids) and less with raft slabs (sand pads dig into the soil). Reason being is that once it starts to rain, the water expands the soil and moves your concrete slab up and when it dries out, the slab goes down. The difference between slabs is that the waffle pod is not dug down deep at all where as the raft slab is so the concrete footings are much deeper and the water logged soil does not affect it too much. Enough of the reasons, lets look at preventative measures. The following are abriged extracts from the CSIRO BFT 18 Foundation Maintanence and Footing Performance: A Homeowner's Guide Plumbing: Check that there is no sewer or stormwater failure Ground Drainage: Grated drain system connected to a stormwater pipe. Eg. A min 90cm concrete pathway around your houses perimeter grated away from the house with water flowing to a stormwater outlet. What I did to my house was build a verandah along one side which takes a lot of water away as you can imagine. Vegitation close to the house: Watering the plants add to the water problem and during summer, adds to the water drying out problem. This is especially so for existing trees next to your house. So.... All in all... water is your enemy when it comes to slab heave. The more you can mitigate with water away from the house the better. If you would like a copy of the CSIRO guide, just PM me with your email. Re: Has anyone rectified slab heave successfully 3May 17, 2013 9:37 pm I have been told that the existing concrete surrounding 90% of the property needs to be replaced with concrete with greater fall and strip drain to take the water collected to storm water/pit/etc. As well as remove a tree that is 3metres away from the house (which I have since done). I am just wondering if someone has had issues.... then implemented the suggested remedies and what if any changes that they experienced following the suggested rectification works. I have a P class slab on piers. Re: Has anyone rectified slab heave successfully 4May 19, 2013 11:27 am A lot of Eastern State homes built towards the end of the drought are now experiencing slab heave but you haven't posted any details about the area you live. The fall away from the house is required by the regulations to be 1:20 over the first metre. If you do not have this, your existing concrete path is not compliant with the regulations. Trees draw moisture by a phenomena known as matric suction. It is possible for heave to be at the end of a slab away from a tree but there are no details given. Three metres from the house is a bit close to have a tree as you probably also had gutter debris problems and it was probably wise to remove the tree. If you search for matric suction on this site, you will find some information that I posted a while back. The article linked below may be of interest to you. http://theage.domain.com.au/home-owning ... 1p5or.html 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Has anyone rectified slab heave successfully 5May 20, 2013 1:17 pm I am in the western suburbs of Melbourne. Yes I have since found out that the concrete surrounding the property does not currently comply as there is no grade so will have to be replaced accordingly with the additional recommendation of strip drains to be installed and divert the collected water to the storm water. Perhaps what my question is, is once this has taken place is it likely that my slab will return to its original state? Re: Has anyone rectified slab heave successfully 6May 20, 2013 1:29 pm Defective concrete paving is just one of the number of possible causes of slab heave, consequently just fixing concrete may not solve all of your problems. There may be other construction defects you are not aware of. 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: Has anyone rectified slab heave successfully 7Apr 08, 2014 7:51 pm There is currently no rectification to slab heave.
There are several reasons for this. If you house has heaved then placing correctly sloping concrete around the house may in fact slow the drying process down but will stop the soil from getting wetter than it already is. The effect of heave will last for years possibly up to 10 years left to naturally dry and as I said will not go back to the house original level. Re: Has anyone rectified slab heave successfully 8Apr 09, 2014 1:17 pm Adam.M The difference between slabs is that the waffle pod is not dug down deep at all where as the raft slab is so the concrete footings are much deeper and the water logged soil does not affect it too much. Wow, Ive never seen this stated so concisely. Does everyone else agree with that? Not that I am querying Adam.M's authenticity, but it would seem if this is true, that one should just do a raft slab whenever on a H soil? But I am aware that plenty of waffle pods are going down on is H+ sites, even when they are on the low side of the road, and beneath the level of the road. Why is this? Just cost? Re: Has anyone rectified slab heave successfully 9Apr 09, 2014 3:31 pm I'd agree that they are deeper but depending on the soil and its capacity to absorb water the depth of the edge beam may not have that much of an influence. Far better to get good site drainage and keep the water away from the perimeter of the house as much as possible as others have stated above. Of more concern to me is the specs for most waffle pod slabs. A depth of 85mm for most of the slab and the edge of 150mm is far too thin for me. Compare a standard brick veneer job I drew plans for a while ago... As opposed to standard BV Waffle Pod slab... Both of these drawings are for standard no-reactive soils. I just think they are way undersized especially for a reactive soil site and am not surprised there are so many problems with them. You guessed it right qebtel, cost is the major factor Less labour to - excavate - build the formwork - place and finish the concrete Less concrete I made a comment here too over something similar. viewtopic.php?f=1&t=62127&start=60 Stewie Re: Has anyone rectified slab heave successfully 10Apr 09, 2014 7:44 pm The reason there are so many waffle slabs implicated with edge heave is during the years 2005-2010 which was the hieght of the drought 80-90% of slabs built during that time were waffle slabs.I have witnessed conventional raft slabs in identical situations heaving almost similar amounts. There is some slight reduction in the moisture ingress under the edge beam of conventional slabs due to the fact that they are dug into the ground unlike a waffle slab which usually is almost at ground level and has a layer of scoria or crushed rock directly under it which promotes moisture flow. The ground at this time was so severely cracked that when the drought ended 2010 water would easily flow under the edge beam no matter what type of slab. The originally slab concept in general was not designed to handle edge heave the original idea was to resist edge settlement and centre heave.The are not really designed to resist the ground heaving but the do to some extent. The rebate depth is not really an issue.This is shown by very few of the heave cases show major brickwork cracking compared to the amount of slab lifting.The majority of the damage is internal plaster cracking and there are several reason for this. One example is a house that has more than 140mm heave over 10m distance with no brickwork cracking but severe kitchen plaster cracking. Re: Has anyone rectified slab heave successfully 11Apr 09, 2014 8:17 pm I have seen both conventional and waffle slabs affected by heave. If builders know they will be building on highly reactive sites and are pricing for the extra work and risk then they cannot turn around and blame it on conditions they knew about. I think it is a combination of defective design and poor building practice that is at the root of the problem. 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: Has anyone rectified slab heave successfully 12Apr 10, 2014 8:36 am I think also part of the reason you don't see cracks in the brickwork is that generally external brick walls have expansion joins every 5m or less depending on the window and door layout so they have a bit of room to move whereas the plaster walls inside do not. I agree though BE - a well engineered design for the site conditions to start with followed by a competent builder doing the right thing is imperative to getting a good result. Stewie Re: Has anyone rectified slab heave successfully 13Apr 10, 2014 10:06 am Stewie D I agree though BE - a well engineered design for the site conditions to start with followed by a competent builder doing the right thing is imperative to getting a good result. Stewie So as someone about the start building how can you double check the design of the slab to see if it would be suitable without getting another engineer to review it? Is it just the thickness/reo/MPa? If so I thought this was just determined in any event by the soil type. http://camdenbuild.blogspot.com.au/ by invite only please pm me Re: Has anyone rectified slab heave successfully 14Apr 10, 2014 12:25 pm Robbie 55 An important bit of info is if you are building on highly reactive soil the ground next to the slab should be graded away, not built up with fill to grade away but be scrapped away sloping to a agi or cut off drain. This is a requirement of the as2870 but was ignored during the drought ground was left flat or sloping towards the slabs. This single thing will haunt the big builders for years to come. On reactive site a engineer is required to design drainage this means site specific design not just a simple generic crossection of a drain Stuck on their drawings. I can give a list of things to look out for Re: Has anyone rectified slab heave successfully 15Apr 10, 2014 12:37 pm Stewie d You are right aj's work well if built correctly and full height doors and windows act like aj's as well Another reason for so much internal cracking is the roof truss span to big a distance now and they are only able to tolerant approx 20mm of movement .A lot of carpenters hard nail the brackets to the top plates when they are supposed to be able move this can be help be releasing the brackets but the damage is done. Most of the heaving slabs have 30-40mm minimum so you can see the problem with the roof truss's 20mm tolerance straight away even if nailed correctly Re: Has anyone rectified slab heave successfully 16Apr 10, 2014 1:43 pm Robbie 55, having a competent and experienced structural engineer is the first major hurdle. Whether you know one or a builder who uses the same guy to design their jobs and you can check previous work is another good step. We were lucky in that all our work was done by the same firm for quite a few years - old school who had been there and done that on a lot of different type of sites over forty years. From what I've read in Victoria a building designer can call up a standard slab design depending on the soil type but I could be wrong ? In NSW as far as I know every DA has to have engineers drawings as part of the CC which has always been the case going back a long way. Tailor made drawings for each house sounds like a way better solution to me. Quote: Is it just the thickness/reo/MPa? Kind of but they have to take into consideration things like point load, where the upper storey rests on the ground floor walls etc too so each slab is pretty much designed from scratch although I'm sure in a lot of cases they have stock drawings that just get altered a bit. Stewie Re: Has anyone rectified slab heave successfully 17Apr 11, 2014 10:21 pm qebtel Not that I am querying Adam.M's authenticity, but it would seem if this is true, that one should just do a raft slab whenever on a H soil? But I am aware that plenty of waffle pods are going down on is H+ sites, even when they are on the low side of the road, and beneath the level of the road. Why is this? Just cost? Wow this is digging up an old post! First of all I am not a structural engineer. My knowledge only goes as far as reading through AS2870, researching and talking to actual structural engineers. From my search, I have heard many different view points. From what I have gathered is this:
- The reality is, it doesn't take much to incorrectly install a waffle pod - A raft slab is much more forgiving - A raft slab takes a few more days and many $1,000's extra - Consumers want a cheaper deal and builders give them what they want! If you read AS2870 in it's entirety and the CSIRO's guide on slab maintenance, you will see that not many houses comply. Eg. next doors house that sits 400mm under my house's level, built using a waffle pod with no fall what so ever. All in all, not everyone will agree with my statement. But as I said, I have heard engineers on both sides and it seems they can't even make up their own minds! Re: Has anyone rectified slab heave successfully 18Apr 11, 2014 11:47 pm Adam.M qebtel Not that I am querying Adam.M's authenticity, but it would seem if this is true, that one should just do a raft slab whenever on a H soil? But I am aware that plenty of waffle pods are going down on is H+ sites, even when they are on the low side of the road, and beneath the level of the road. Why is this? Just cost? Wow this is digging up an old post! First of all I am not a structural engineer. My knowledge only goes as far as reading through AS2870, researching and talking to actual structural engineers. From my search, I have heard many different view points. From what I have gathered is this:
- The reality is, it doesn't take much to incorrectly install a waffle pod - A raft slab is much more forgiving - A raft slab takes a few more days and many $1,000's extra - Consumers want a cheaper deal and builders give them what they want! If you read AS2870 in it's entirety and the CSIRO's guide on slab maintenance, you will see that not many houses comply. Eg. next doors house that sits 400mm under my house's level, built using a waffle pod with no fall what so ever. All in all, not everyone will agree with my statement. But as I said, I have heard engineers on both sides and it seems they can't even make up their own minds! I agree with you Adam.m I think it will be sorted out in court and the main arguments will be who is responsible for drainage . is it the builder ,did they follow the engineers drainage design ? is the engineers drainage design adequate , did it comply with AS2870 ? is it something the owner has done regarding drainage ? I my opinion builder and engineer will carry the responsibility and the builder taking the largest load. Re: Has anyone rectified slab heave successfully 19Apr 12, 2014 1:19 pm To answer OP question, I have been a builder for over 40 years and I don't know how to fix a slab heave. The reason is that when soil heaves up due to ingress of moisture is that it will stay up even after it dries out. It seems that in domestic construction the loads are not enough to push soil back down. In my reports I have recommended partial demolition and reconstruction of slab to get down to designed levels. It would be interesting if anyone else has different experience. 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: Has anyone rectified slab heave successfully 20Apr 12, 2014 3:07 pm I think it is a bit of the old locking the gate after the horse has bolted unfortunately. Once it has happened I don't think it can be easily fixed. Mostly it appears that the site drainage has a much bigger impact on this occurring than most builders and clients think. I wonder how these guys are going to cope in the future viewtopic.php?f=19&p=1161877&sid=1d065577add46708c5234806432739cb#p1161877 Stewie Hi All, we are starting to think of building with Masterpiece Builders in Victoria, has anyone had any feedback or experience with them 0 13603 Hi we are looking to talk to people who have built with them recently. We have signed mid range built contract but identified that a lot of things are not included.… 0 742 I work with owner, he/she is my man on the ground and I instruct them when to visit the site and take photos and I have other tools in the bag. 4 15284 |