[Interview] Toowoomba Soil Types For New Home Construction
An early part of every new home building project is identification of the type of soil on the property and its impact on the build. In this interview, Patrick Neville from Stroud Homes Toowoomba will take you through what you need to know about soil types, soil testing and the implications for your new home.
Mick: Welcome back listeners. It’s Mick here and I’m talking with Patrick Neville from Stroud Homes Toowoomba and today we’re going to be talking about something that everyone goes through on every new home build that they do, is looking at soil classifications, everything you need to know about soil testing, especially how that relates to the Toowoomba area. Patrick thanks for jumping on the line.
Patrick: No problem at all.
Mick: We spoke a bit the other day about this sort of stuff and I know, when we used to live in Toowoomba, around BBQ conversations and things like that when people were building a home was the different types of soil types that were in Toowoomba, black soil and brown soil, the impact that they had. I guess the one of the subjects we need to talk about are soil classifications – what are they and how do builders and experts in the trade sort of refer to this and talk about this?
Patrick: They really do have an impact on every build. It’s sort of the houses are generally pretty similar to build once you get out of the ground. It’s what happens getting out of the ground that can be quite costly when building. Generally there is about 6 different classifications that we run through, starting off at Class A – which is stable and nonreactive, definitely not really heard of in the Toowoomba region.
Patrick: Generally when builders and especially engineers they want to talk about, they call it the “Y’s” or pretty much the amount of movement that can occur. In the Class A you’re looking at about 0-10mm of movement.
Mick: Is that like a weekly variation or is that a movement over time or is that like settling after or during a build
Patrick: That’s just sort of the maximum range of movement. In between extremely dry and extremely wet, you can expect the soil to move 10mm.
Mick: Okay, sure.
Patrick: After Class A you have Class S and this you get sometimes here around Toowoomba, dwindling down to that also very rarely, and that’s generally between 10-20 Y’s. This is sort of deemed as slightly reactive clay sites.
Mick: Just to be clear, when you’re talking about the Y’s, that’s just a unit of measurement that they use for soil testing.
Patrick: Yeah exactly.
Patrick: After Class S, you have Class M, which starts to happen regularly and builders’ eyes light up when they see a Class M soil, normally means it’s going to be a very good quality build and quite an easy slab. M – between 20-40mm Y’s with the M site.
Mick: And there are areas in Toowoomba that are normal M class?
Patrick: Yeah. It really depends on the area but once you sort of get out the black soil and into the nice ready soil or very clay soil, it tends to be M-type soils and quite easy to build on.
Mick: Okay sure, so what do we have after that?
Patrick: After M you head up to first of the H’s, which is a H-1 and this generally goes from 40-60 Y’s, 60mm of movement.
Mick: Sure, okay.
Patrick: This may experience a high amount of ground movement as a result of soil conditions and moisture changes that happen obviously between wet and dry. After that we head up to the H-2, which is 60-75mm. This is also deemed highly reactive clay sites. Then after H-2 you have the dreaded E, which is 75mm and above, pretty much anything above 75mm will go E and sometimes you hear sites go up to 120 or even more Y’s, so you have a lot of black soil heading out towards Dobie, and that kind of area it’s just all black soil. You can expect sites to be up around 120 Y’s.
Mick: Alright, and this needs to be done I guess on any block that you’re going to look at building on. Is that correct? You need to go in and get the soil tested first?
Patrick: Yeah that’s one of the first parts of the preliminary agreement. It really does affect, it’s the main thing that can affect the contract and the pricing of the house.
Mick: It’s a bit of a gotcha their for people who are buying land off a developer or doing their own sort of build, where they should possibly lock that in as a contract condition beforehand?
Patrick: Yeah, it’s kind of a given. Definitely up here around this region is people like to make their contract subject to soil test and get one of them done before signing on the dotted line.
Mick: And who does the soil testing? The builder does or the developer does or the specialist?
Patrick: It really depends. Obviously the developer can get it done. Some of them do, but then again they might not want to if they think that the soil is going to go badly or poorly in their area. They contact generally mostly get engineering firms who have a soil technician that can do this or there’s a couple of specialist organizations that specialize in just doing soil test.
Mick: Is there a ballpark figure you can give folks for that?
Patrick: Yeah, approximately $500, you might pay a little less, a little more, depending on how far away from their office you are or the kind of site they’re having to test.
Mick: As far as organizing that, if people go through Stroud Homes and building Stroud Homes, is that something you guys look after, getting that all done?
Patrick: We prefer to look after the soil test if we can, just that way we can be confident in the quality of the test and who’s doing it. When you get a soil test done, it really becomes up to the engineer whether they want to accept it to do their slab design. We generally use the engineers that are going to do our slab design to do it. That way there can’t be any quarrels about a poor soil test.
Mick: Sure, one less aspect to place blame on I guess.
Patrick: Yeah exactly.
Mick: In the Toowoomba area, you mentioned your red soil areas and your black soil areas, is there something that you can sort of generalize around a city or an area what the sort of soil rating will be or is it something that really varies from spot to spot within the city?
Patrick: It’s really hard to generalize an area because you can have 2 blocks side by side, they might be 50 meters apart and one could be an H or an M and the bottom one could be a H-2 or an E. It really just depends. A good example of this is at a [6:52] at the moment there’s an estate on a hill and the bottom blocks or the lower ground is in a little bit more black soil, so they’re going H-2 and E but if you go off the hill a little bit, some people being lucky enough to get an M site and that’s within 100 meters of each other. It really becomes hard to generalize areas as such.
Mick: Is there any statistics on that that you’ve got for the area, like how much of Toowoomba is an M class or those of historical views?
Patrick: No not really. Generally around the north and that kind of areas out towards high fields and keep going north is generally has been pretty good, recently we’ve noticed. As soon as you start heading sort of west out towards Dobie way, the land out there is poor for building; great for farming by the looks of it but very poor for building.
Mick: Patrick so we talked a bit about what the bit of soil types are and how they get tested and roughly where they fall in the Toowoomba area, what’s the impact? If it’s someone who’s looking at building early in the process, what impact does it have on the actual build, possibly cost-wise or time-wise between say your S and your M’s, and then your H’s and your E soil types.
Patrick: Basically it depends what kind of slab you’re going with. There’s 2 different types of systems that I generally use, the waffle pod slab and then a [8:20]. Around the Toowoomba area we always use the [8:23] just because we don’t have many S sites. With an A or an S site, you can pretty much just have your general slab with just an edge beam and maybe a few crossbeams but as soon as you go into an M, you generally have a fair few cross beams throughout the slab and a nice big thickening beam around the outside, generally all of these around 300mm x 300mm and then once you step up from there it starts to increase in size and depth. That’s sort of 2 big things that start to impact on the pricing. They take a lot more steel and a lot more concrete once you start going deeper and wider with your edge beams and thickening beams and crossbeams throughout the slab.
Mick: What’s the thing in there? Basically you’re just making it a stronger sort of integral slab so that if the soil shift that there’s not going to be cracking in the slab, as opposed to a stable soil type where you can get away with a lot less?
Patrick: Yeah exactly. We need to build it strong enough to withstand, so if you have an S or an M site, it can only move like 10-20mm, which is not much at all but if you go up to an H-1, you could be up to 60mm of movement, so we need to build a slab to be able to take on 60mm of movement.
Mick: For someone who’s buying or trying to price their new home design, will they get a fee in their design process or the quoting process or is that like how they compare one block for the other, price-wise without regard?
Patrick: At Stroud Homes here we offer a free site evaluation so we’d love to go outside and us having a lot of experience we can generally have a fair guess of what the soil type is going to be and we can allow that in our initial quote but generally it won’t get picked up until the preliminary stages, once we do actually get a soil test done and start looking at getting our slab design finish. That’s when the truth really comes out about what’s in the soil.
Mick: Alright fair enough. What’s the downside, so if you don’t get this soil testing right or you don’t get your slab right, what are some of the things that can happen?
Patrick: The main one is just the general movement in the slab and that just, depending on the severity of it, will lead to worse and worse things. Obviously when you have a little bit of movement some cracks might start appearing around the eight joints and the control joints around the perimeter of the outside. Some of the rings might start to peel away and then if you have even more movement, some crack starts appearing in the slab. Tiles will start to crack and if it gets really bad your corners and clusters will start to slid away.
Mick: Once it gets to that stage, is there anything you can do to fix it or is that kind of terminal?
Patrick: It just depends on severity really. I guess you’d have to get an independent person to weigh up whether the cost of fixing it is really worth it. There is a processes of digging under, they call it underpinning. You can dig under it and put more pins in them and that kind of things, but once it sort of starts, I really think it’s a downhill slide. There’s been a few horror stories around Toowoomba lately of a couple of houses, fairly new houses, we’re talking about a couple of years old, having to be completely pulled down just because of the poor slab design.
Mick: It’s basically one of those things that you get it all sort out early and peace of mind, not a worry.
Patrick: Yeah exactly, to some people, you just got to explain to people that the cost is worth it in the long run. There’s nothing we can do to not go ahead with it. The council determines.
Mick: Patrick we talked about the impact on the cost part as far as putting together the slab. Once we’ve actually get into the construction process, is there any impact then on the time it takes to construct to the complexity depending on the soil types?
Patrick: A great myth about it is that once you go into a H soil or a H-2 or an E, had a toll on the slab. A lot of the extra price actually comes in to the plumbing as well. One thing you’ve got to avoid is sort of generating wet spots or I tend to call them hot spots; great things for this, a leaky or damaged pipe. These days we incorporate, once we go about an M type, we start to incorporate expansion joints and ball joints into the sewer and stormwater aspects of the plumbing and these tend to incur quite a decent amount of cost as well.
Mick: I guess that’s just unavoidable. You’re heading off future problems by treating all that early.
Patrick: It is, exactly that. It’s taking a really proactive stance to not letting water lie around your house in bad spots.
Mick: If folks are listening to this and they’re looking at getting a block of land or going through a building process in Toowoomba, you mentioned you guys do a free on-site check. Can you just describe what happens there?
Patrick: Generally if you’ve got a block of land and you want to know a little bit more about it, just give us a call and we’ll come out and have a look over the site and a couple of things we try to figure out is know the kind of soil that would be there, also the cut and fill that might be required. We’ll also go through the optimal house positioning, where your design would work best on the block and from there we’d probably look at preparing a site plan for you to have a look at as well.
Mick: How can folks get more information and contact with you guys?
Mick: Thanks Patrick, that’s been really good, opening up the conversation there about the different soil types and giving a bit of background I guess; approach that stuff beforehand and if you’re going through that building process it’s something everyone, all of us needs to know when we’re going through and starting a new build. Patrick, thanks very much for your time.
Patrick: No problem at all Mick.