Concrete Slab vs Timber sub floor?

We are having plans drawn up and looking at building in the next 12 months, a 2 storey house of approx. 375sqm. We have a block in the eastern suburbs of Melbourne which looks flat but has fall of about 700mm from one side to another, M classification. We are not sure whether to go slab or timber sub floor. Initially we thought slab was the way to go, solid foundation less chance of termite attack etc. However our building designer has suggested we would not need to cut and level the block if we go timber sub floor and can then have sub floor ducted heating.

What are peoples' thoughts on the 2 options. It seems most people are building on slab but why? For those who have built on slab how effective is ducted heating through the ceiling? Also how do you lay solid timber flooring over a concreted slab. What are the cost differences between the two options. Any comments would be much appreciated.

I'm no building expert so I can't argue which is more expensive or prone to movement over the years but my choice is a concrete slab. One of the reasons for me is that houses on stumps are allways noisier when people walk around, I'm in a house on stumps at the moment and you can here someone walking around down the other end of the house. Also building on stumps might save you from a site cut but that 700mm is gonna go somewhere and more than likely it means in some areas of the house you are going to have steps from the doors to outside. I personally hate having to walk down steps to go outside. With the landscaping ideas and fancy stone look retaining walls that are around today a cut of 700mm need not be a bad thing - with the right gardens and so on it can be a nice feature.

The drawbacks are having to pay for outside ground drainage in cut areas and no under floor ducted heating - both very minor issues IMO.

Thanks Mozzie for your advice, as all feedback is appreciated.

The noise issue, I thought, could easily be overcome by laying particle board over the sub floor frame and installing floorboards over it. This would also help insulate the subfloor to help achieve our 5 star rating. You are right about steps as we would have approximately 3 steps on the west side where our laundry door is, and like you, my preference is for less steps around the perimeter of the house. I am still not sure. Anyone else have any comments?

We built on slab because of its strength and durability, no need to restump in the future. I think anyone would be mad to build on timber sub floor in this day and age. Anyway that's my opinion.

Subfloors can be done in other ways other than traditional stumps and I'd imagine "stump" technology may have gone far enough that re-stumping is not a major issue going forward (concrete stumps for example).

One solution I've seen below is as below....strip footings along the side, brick piers down the guts, top the brick piers with steel beams, and lay bearers across. The added advantage was that because there were no stumps there was quite a good clear storage area under the house, even with all the duct work.

http://i241.photobucket.com/albums/ff2/mikeb1968/Foundation.jpg

I don't think you need to be "nuts" to use a sub floor, depends on your site conditions (steeply sloping....not everyone lives in the flat lands of Melbourne'e West like me) and in some cases you may have a more interesting house if you work with the contours of the land rather than fighting against them.

My thoughts......

We went with stumps for a couple of reasons. One was so our heating would be under the floor with the vents in the floor. Another reason was to reduce the chance of water entering the house in case of torrential rain and blocked drains causing water build up on the property. I guess the real reason for me was I prefer them.

Also keeps the "drop bears" out...sorry couldn't resist....

I would never consider building on a slab - which is more prone to termite infestation than piers by the way. You can physically get under a house on piers to check, a slab house they can come up through the concrete straight into the framing.
Bearers/joists, particle board and framing can all be done in termite treated products for about 10-15% more than standard regardless.
The benefits of being able to get under the house are many, whether it being to relocate cabling, phone outlets or to move bathroom fixtures around at a later time if need be.
Timber flooring is not a problem to lay over concrete using hardwood battens. Houses on piers are always covered with particle board flooring before timber/carpet/tiles are laid etc. You can use underfloor insulation between the floor joists also to achieve your 5 star rating.

I personally will like a concrete slab, as other has said because it seems sturdier.

But with the timber subfloor, you can not only ducted your heating in the subfloor, you also can CAPTURE ALL of your greywater (bath, shower, laundry etc) from your ground and first floor, and used them for your garden.

I'm voting for stumps. I think it's good to be off the ground for many reasons: air flow, floods, bugs, and access to name a few.

Those factors are even more important in places like Brisbane. Having lived there in a low-set modern and a high-set old timber house, I am totally convinced of the wisdom of stumps in that environment.

I asked a builder friend of mine (retired) about the whole stumps versus slab debate and he was very firmly of the opinion that the only reason new houses were using slabs was that it was cheaper.

Am I allowed to say without that timber subfloors probably require a higher degree of care to build and more skillful tradies.

Building a timber subfloor would also be a lot slower....less production....less dollars...gets back to Cabinfevers comment...overall reduced $ turnover.

We're building in inner-east Melbourne at the moment. For thermal reasons, would have preferred slab, but as we're in a flood overlay and had to have our floor a metre(!) off the ground, we ended up with:
- concrete strip footings around the edge
- these had screw piles going into the ground
- down the middle of the house are more screw piles
- brick footings and piers going up 1m
- wooden bearer on top of the piers and strip footings

Here is what it looked like during construction:

http://i229.photobucket.com/albums/ee6/tastony/base_stage1253_smaller.jpg

http://i229.photobucket.com/albums/ee6/tastony/IMG_1138_closeup.jpg

Will see how it works out once it all gets finished...

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I've lived in all of them.
8 foot stumps, slab on ground and 3 foot concrete stumps with timber floors, and variations of 12"stumps etc

I prefer stumps.
You can insulate under them.
You can get in there and run cables etc- + visit the red back spiders while you're at it.'
Check for moisture while under there.
Run ducted vaccumms there.
Move kitchens and things without (SLAB) restrictions

And hey - even hear if there is a bugular in yoru house.

Slab on ground - nada - except to get some thermal mass where you need it - but even suspended slabs on stumps can do that - if insulated properly.
Steve

I had a chat to my builder friend just this morning and this thread came to mind, so I asked a couple more questions.

He was particularly critical of slabs' vulnerability to water and roots. Water or roots could crack a slab and once moisture got in it can cause concrete cancer that can never be detected until it reaches an advanced stage.

He said stumps went down much deeper than slabs and so were less subject to movement, either from water or roots. He also preferred slabs because a house can be re-stumped, but not re-slabbed.

Further to the cost issue, he said slabs required much less materials than stumps, less skilled trades, and much less time.

He said stumps also provided a stronger base in that a typical stump will be rated to carry roughly 30 tonnes, which is far over its typical load.

-- I'm just reporting his opinion here, and keep in mind that as a builder he almost always built on stumps so obviously has a preference for that method. I'm sure a 'slab builder' could also list many positives for that method. --

Thanks everyone for your comments and postings re: slab vs timber sub floor. Its interesting that some people have commented that a timber sub-floor requires a quality builder with greater skill.

In our subdivision of only 11 new homes, the 2 most expensive, quality built houses have built on timber sub-floor while all the others have built on concrete slabs. We are building a quality, 2 storey custom home, and the choice is not necessarily a financial one, but what is best from a building and longevity point of view. It seems that timber sub floor is leading the way. We may just have to live with some steps on our laundry exit, although our alfreso side will end up level with the land.

Any other comments would be much appreciated.

I built on "stumps". A lot of brick piers and concrete piers. My house is a split level design in inner Melbourne.

The good things that a house on stumps are listed above.

Also with stumps you can have a cellar. My cellar is huge, and have told my partner that it is where he can keep his tools of the trade, and having more room in the garage. So extra storage is great. Also my partner is very into firearms, expensive one too. As the cellar is double bricked, he is going to install a steel door in a section under the stairs in the cellar (and that is concrete). I like this idea as the firearms wouldn't be in the "house".

As a chippy/builder, my partner thinks that stumps are better. He has seen slabs slapped together, happy slappy styles and as a result as noted her in homeone, you get frame overhang etc.

Also from a builders perspective, if you have a problem with say plumbing with th pipes, fixing it is an expensive excercise with some slab damage which he saw on one job.

From my understanding, project builders will not do stumps, only slabs though.

I kinda made that comment but wasn't exactly what I meant. Timber subfloor construction requires carpenters which IMO is perhaps a higher skilled trade than that required for slab construction.

It's not dissing those guys who are able to lay a slab in a day - when I started my career I started in the ye olde public service where they expected engineers to know what the tradies were doing. I worked on a construction site for a couple of weeks - tying off vast quantities of reinforcement and pouring concrete quickly is not an easy job - frankly I was stuffed by the end of it....but by the end of it I was relatively useful. Put me with a carpenter and by two weeks I'd probably be at the point where I could successfully staple gun by hand to a frame.

So you need tradies which have the skills which are in shortage, and therefore waiting for those tradies will slow down the construction progress, and then actually build the sub floor is time consuming.

Like everything it comes back to $$$, and I think that dictates the popularity of the slab.

What is the first major payment that you make on a house?

Generally the foundation stage - the quicker the builder can get down the slab the earlier his cashflow improves on the job. Most peoples experience with building will probably be that the slab goes down extremely quickly.

Makes perfect business sense to go with a slab when you can and to convince the buyer its the best choice (sometimes it is), gets the $ in the door ASAP.

Putting down a timber sub-floor is fairly straight forward provided the piers are reletively level. These days bearers and joists are termite treated LVL timbers - not the old green hardwood of yester-year. They are gun-barrel straight and need only to be put down 'square' for the frames to go on top. Generally the particle board flooring (termite treated too) goes over the joists before the frames are stood up.

Myself and my girlfriend are going to build a house. I would like to get a house built on stumps for the reasons stated by everyone else. However it seems a lot if not all of the major builders only build on a slab. Does anyone know any major builder that will build on stumps instead of a slab?

Glen

Slab by far and away the better option - I agree wholheartedly with the drumming comment as well - timber is noisy

Don't forget you could go with a suspended concrete slab suported with piers if you want to get access to pipe underneath it - good for storage of large items like ladders as well. By the way, yep its exy!!

As for termites - this one is the no brainer of all no brainers - if you specify a "treated" softwood frame it will not be eaten by termites and never requires inspection. By the way, yep it costs more but have you ever priced pest control or considered the cost of patching a house that's had termites and the resale consequences.....very ugly. As a rough guide you can add about one third the cost of your frame if you want it treated.

JB