Ask RiotACT: High "M" class soil in building contracts?

The extra work and materials is more stiffening in the slab using extra foundations or piers.
M class is 3rd lowest out 7 of classes of soil.

http://www.build.com.au/building-reactive-soil-sites

Maya123 said :

I have two types of clay on my block, but this wasn’t known until the old house was removed. (Although I suspect the soil tests weren’t done as thoroughly as they should have been.) It was discovered then and I needed more foundations, adding several thousand dollars. Better this is done though, rather than leave the risk.

Sorry, I should have said concrete piers, not foundations.

I have two types of clay on my block, but this wasn’t known until the old house was removed. (Although I suspect the soil tests weren’t done as thoroughly as they should have been.) It was discovered then and I needed more foundations, adding several thousand dollars. Better this is done though, rather than leave the risk.

I don’t know if caught out is really the correct term. M class soil will require considerable more excavation of footings which will result in additional concrete and reinforcement being required. Non of this is free and unless you have had a geo tech report done prior to construction hard for the builder to anticipate.
Re the comment on rock cutter no Civil contractor in Canberra will allow for rock unless it is identified at tender. Again it is not reasonable to expect a builder or contractor to allow for latent conditions unless you identify the risk when negotiating your contract.

In general you will be quoted on a blue sky scenario and then be expected to take on some of the risk. the alternative is to have a lump sum with no risk which no one would do as it will be high to allow for the risk, good for you if you hit rock for instance bad for you if there is none..

Yup! Happy to pay the extra because it means a much more solid foundation and we were aware of the soil conditions before signing (you need to read everything!). Also, it was an extra $5,000 (back in 2007), which sounds like a lot, but is nothing compared to the total cost of house and land; it was easily absorbed in the contingency budget.

The other thing to consider is your relationship with your builder – we got on really well with them, but our neighbor (whose house was being built at the same time by the same builder) argued every expense. In the end we didn’t get charged for a lot of stuff and it was quite a pleasant build, but I’m pretty sure the neighbor paid extra and had a lot of stress 🙂

That’s all part and parcel of choosing to build, as opposed to buying a ready house. I got caught out with several thousand extra for ACTEW wanting to put the power underground, even though all my neighbouring blocks have overhead power.

I know of others who were up for several thousand extra for a rock cutter.

There’s always variations and cost overruns when you choose to build.