Concrete Slabe V Joists and Bearers

[Jimbo2612]

I have been told by a "potential builder" that the cost of joists and bearers is equivelant to a slab + a new car. This seems a little odd to me. The block is sightly sloping so some excavation would be required with the slab.

Anyone faced the same problems? ProbablY a question that gets asked all the time.


Thanks

[Terry1]

Hello Jimbo,In this area at least we use three different methods depending on the block (amount of slope etc)Most of the builders around here use raft slabs exclusively with waffle pods becoming very popular lately due to the cost savings .Me and my son like to do strip footings when working on our own spec homes for varied reasons,extra height is easily achived which makes it easy to get rid of water,ease of spliting floor heights,I also think the same house looks much more impressive when sitting up compared to the normal method of sitting the raft slab as low as is legally possible.We are doing a spec home at the moment and we have dropped the garage floor down a metre from the house floor which gives you a nice run up the driveway.The house next door has a raft with the garage down one course and it has a really steep driveway which I wouldn't fancy driving up at all.We are also bricking up (we are also sub contract bricklayers) a bearer and joist house at the moment but am not sure how it is costing out exactly(but it is favourable compared to rafts in this area )as my brother owns a transportable home company and he buys direct,also his carpenters are very familiar with this method.So his costs might not apply to you.Also there are numerous steel flooring methods in place which might be worth looking into.These can be used with either sheet flooring or hebel.I hope this is of some help.Regards Terry

[dazzler]

Hi jimbo

We just built a new place that had a 1m fall over the length of the house (26m long).

They did a cut and fill and then a slab as the cost of bearers and joists was over the top (maybe 30k ish).

So it sounds about right to me. Plus using termimesh or similar on the slab stops any termite issues down the track.

[Jimbo2612]

Thanks guys,

Is there an issue with waffle pod slabs on reactive soils? This area is renowned for its soil issues. This is where it may be better to utilise one of the steel flooring solutions where the height can be altered. Not sure I suppose it is a risk issue.

[silentC]

Best off to speak to an engineer about it. You'll need to get a soil test done no matter which way you go and that will tell you what best to build on it. It's a better idea than trying to decide how to build first in isolation of what you're actually building on.

FWIW half our house is on an infill slab and the other half is on bearers and joists. The advantages of the slab are that it was quick (read less labour) and it works well as a mass for absorbing and slowly releasing heat and staying cool in summer. The disadvantages are that you only get one go at things like plumbing and termite protection and there's no option to get under there and change things or use it for storage.

The downhill side of our place is nearly 3 metres above ground level, so I have heaps of storage under the house.

If you are on a flat block and you are paying a builder, slab is probably going to be the way to go. I reckon if you are building yourself, the price of concrete makes bearers and joists cheaper - but you have a few weeks work ahead of you before you can start standing frames. A slab takes a couple of days to box and one to pour. But you have to get the trades in first, which could hold you up.

With bearers and joists you can plug on and they come whenever they can fit you in. It still might hold you up but you can more or less get the roof on before you need a trade on the site.

[Grunt]

I'm building myself and we've chosen bearers and joists from a cost point of view.

[Yonnee]

It would depend on the slope of the block, and the deals that the particular builder has going with either concrete companies or excavators and dump trucks. If they had a good deal with their concreters then of course a slab is going to be cheaper than stumps, but a major cut&fill can be pretty expensive. And if you had a reasonable slope, you'd have to factor in the cost of retaining walls too.

As silentC said, with stumps, you can do all your plumbing and any other lower ground work even after the roof is on. Our sink outlet was in the wrong spot in our kitchen when our house was being built. You should have seen what they had to do to fix it. Cut a 2 foot square section out of the slab to re-route the pipe, then re-pour that bit.

And if in 10 years you want to renovate your kitchen or bathroom... with a slab, all your outlets have to be in the same spot.

And with stumps, all your plumbing can be hidden under the house instead of coming out the walls and down.

[Grunt]

One other thing.

I'm doing a strawbale house which means that I can put the load bearing walls straight on to the floor. I don't have to have foundations like I would if I was building a brick veneer house.

Having to do the foundations for the brickwork adds considerable cost to building on stumps.