Our Slab and Underground Works...

Three words... plan, plan, plan!

If you're thinking of building on a slab, this is probably the most critical point in the project! Forget anything and it is too late... anything that needs to run under the slab or up through the slab MUST be in place prior to the pour - no second chances!

Some of the things to think about are;

Plumbing - not only where does it go, but other factors, for example, do you want your grey water and black water separately plumbed?
Gas - yes I know it's part of the plumbing, but if you are having gas kitchen appliances, natural gas BBQ or gas hot water, your plumber will need to know the usage ratings and the exact locations they are going to be installed. He needs this so that he can size up the pipe work to ensure you have enough gas where you need it. We actually 'lost' the gas pipe for our hot water booster, but thankfully we had allowed a 'spare' connection in that area for a BBQ so we could use that - the alternative is thousands of dollars in additional works to get the gas line installed afterwards.
Electrical - do you need any electricals in places that require penetrations? For example, does your kitchen have an island bench with power or water?
Communications - this is different to electrical, in most circumstances you cannot run data / telephone in the same conduit as your electrical.
Termite treatment - I used 'Kordon' termite barrier, which requires all penetrations through the slab to be sealed with their product. This means that each penetration will cost you money, so find that balance!
Anything else - you may want to install a safe that is poured into the slab (we didn't think of this but some of our friends have done it and it's a great idea).
Services cupboard / riser - we have actually run our ventilation, electrical, water, telephone / communications and security back to a central location in the home, this allows us to isolate all of our services in one cupboard should the need arise. It also gave me a point to run EVERYTHING back to, that's out of the way, but easy to get to.

My advice would be to sit down with each of your trades prior to the final slab design being created to ensure that every service is thoroughly thought through and incorporated into the layout.

After planning...
Once you've done all of your planning, make sure that you follow these steps;

Make sure your Soil Report is available - the Engineer will need this to figure out the design of your slab (thickness, supports, reinforcing, etc),
Have a site topographical study done - this allows your Engineer to design how high your slab needs to be and how much cutting / filling will be required (cutting and filling costs thousands of dollars, so this step is critical at an early stage so you can put budgets together effectively),
Once the slab is designed run it by your Architect to make sure that the overall heights are still correct and the slab design matches the home design. Also, a good Architect is quite practical and will be able to help iron out any services placement issues if you ask nicely,
GET EVERYTHING QUOTED ON!!! - make sure that every trade involved has provided a fixed price to conduct their portion of the works. This is a curly one and we were caught out on more than one occasion by a task that no one had quoted on. This was normally followed by a conversation that usually ended with 'nah mate, we don't include that in our price, we can do it if you want to as a variation, but that's normally done by the...'. The translation is 'we didn't think of that, so now you're going to have to pay us extra' or 'we didn't tell you about that because this is where we make the money',
Go and inspect people's work - everyone will tell you they do a better job than everyone else, go and see for yourself,
Get referrals from associated trades - ask the tradesmen you are planning to use who they've worked with before. Generally speaking they'll remember people that have done a good job, because it makes their job easier.

Getting Underway...
Now that you've chosen who will do what and you're comfortable with their skill and pricing it's time to get things underway;

Have the site levelled - a good tip is to think about what soil will be needed or need to be removed once you do your landscaping. It will be a lot cheaper to have the good top soil left in a pile or excess removed from site in one go,
Have a Surveyor mark out the slab - it'll cost you $300 - $400, but once it's poured you can't move it, so get it done by a professional with insurance,
Coordinate all of your trades so that they come to site and mark out where they need their trenches dug at the same time. This will ensure that appropriate (and legal) separation is maintained. If they refuse or are unable to come to site, at least make them draw on a scale drawing exactly where the trenches are to be dug,
Once everything is marked out and has been checked by all parties, meet your slab contractor onsite and go through everything with him - generally the slab contractor will do the trenching for the other trades if you ask them to and the advantage is that they will dig out everything in the right order, so that one trade's trenches aren't accidentally backfilled by another trade as they are digging theirs,
Now get your trades back on site to install their services as close as possible to the pour date to minimise any risk of vandalism or environmental damage - tip: go one size bigger than you need on all conduits / pipe work, it will only cost a little more, but it gives you the flexibility to add things at a later date that you didn't think of, for example I originally was going to have a single phase power connection, but luckily, I requested a larger conduit, which allowed a three phase connection (3 phase motors are a lot more efficient than single phase),
Once all trades have completed their work and have given the go ahead (often inspections are required for underground services), have the slab contractor prepare the slab for pouring,
Coordinate your Building Inspector to sign off the pre-pour inspection,
Have the slab poured - note: if the slab is not flat and even you will most probably be up for additional fees from your structural trades and floor covering trades to level everything up, so make sure you're comfortable with their quality of work before you start.

What we did...
We have a floating slab on waffle pods

Due to the nature of our design, we wanted a very large thermal mass inside our home, as insulated as possible from the outside world. To achieve this we have utilised 'Waffle Pods' on the ground, with 100mm floating slab over the top.

Waffle Pods
Waffle Pods are polystyrene boxes that form a void between the ground and the slab, they are used for a variety of purposes, but in our case it was to provide a thermal barrier between our house and the Earth. The most common forms of insulation (Batts, Double Glazing, Thermal Blankets, etc) work on the principal of creating stationary air pockets to prevent the transfer of heat via conduction and convection, which is why we have chosen to place our slab on top of what is essentially insulation (polystyrene) and a whole lot of air pockets.

100mm Slab

Thermal Properties - to provide our home with passive heating and cooling we required a 'heat sink' that would store and release heat, helping to even out the temperatures inside. The walls are all 150mm concrete insulated with 65mm of EPS on each side (see 'The Environment' page), which gives us an enormous mass to slow down heat transference, however we also needed something that we could use to cool us in winter and heat us in summer - that's where the slab comes in. Our eaves have been designed to stop any direct sunlight hitting the slab during the hot months, so it's nice and cool, but during the winter months they allow full sunlight to enter the house and heat up the slab. This heat is built up during the day (stored in the slab) and slowly released overnight.
Design - the slab is a 'floating slab', called a floating slab because it 'floats' on top of the ground with 'beams'(deeper trenches) around the perimeter to hold it in place. Because of the weight of the concrete walls, our house also has 'beams' under the walls to prevent any cracking or movement under the huge weights being sat on top of it.
Finishes - our slab mix used a variety of different stone because we had the intention of polishing the slab instead of using traditional floor coverings. As it turns out, we didn't polish it, but if you did want that look, we found that Readymix were the most helpful; they offered us a variety of stone in the aggregate at no additional charge - a very big saving! You can also 'seed' the top layer of the slab as it is being poured with whatever you like (some people have used stone, pieces of glass, coins, metals, etc), once the slab has set you can have it polished and sealed (this will remove any sharp edges of items you may have 'seeded' in). This is well worth doing if you ever intend to have polished concrete (it will never be this cheap again - once it's down it's very expensive to change it). 'Seeding' is throwing handfuls of whatever on to the top surface of the concrete during the pouring process just before it is levelled out.


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Out of the ground (Slab and underground works) The structure (Walls, windows and roof) Fit out (Plumbing, electrical, tiles, plaster & paint) The Environment Bits & Pieces
		Our Slab and Underground Works... Three words... plan, plan, plan! If you're thinking of building on a slab, this is probably the most critical point in the project! Forget anything and it is too late... anything that needs to run under the slab or up through the slab MUST be in place prior to the pour - no second chances! Some of the things to think about are; Plumbing - not only where does it go, but other factors, for example, do you want your grey water and black water separately plumbed? Gas - yes I know it's part of the plumbing, but if you are having gas kitchen appliances, natural gas BBQ or gas hot water, your plumber will need to know the usage ratings and the exact locations they are going to be installed. He needs this so that he can size up the pipe work to ensure you have enough gas where you need it. We actually 'lost' the gas pipe for our hot water booster, but thankfully we had allowed a 'spare' connection in that area for a BBQ so we could use that - the alternative is thousands of dollars in additional works to get the gas line installed afterwards. Electrical - do you need any electricals in places that require penetrations? For example, does your kitchen have an island bench with power or water? Communications - this is different to electrical, in most circumstances you cannot run data / telephone in the same conduit as your electrical. Termite treatment - I used 'Kordon' termite barrier, which requires all penetrations through the slab to be sealed with their product. This means that each penetration will cost you money, so find that balance! Anything else - you may want to install a safe that is poured into the slab (we didn't think of this but some of our friends have done it and it's a great idea). Services cupboard / riser - we have actually run our ventilation, electrical, water, telephone / communications and security back to a central location in the home, this allows us to isolate all of our services in one cupboard should the need arise. It also gave me a point to run EVERYTHING back to, that's out of the way, but easy to get to. My advice would be to sit down with each of your trades prior to the final slab design being created to ensure that every service is thoroughly thought through and incorporated into the layout. After planning... Once you've done all of your planning, make sure that you follow these steps; Make sure your Soil Report is available - the Engineer will need this to figure out the design of your slab (thickness, supports, reinforcing, etc), Have a site topographical study done - this allows your Engineer to design how high your slab needs to be and how much cutting / filling will be required (cutting and filling costs thousands of dollars, so this step is critical at an early stage so you can put budgets together effectively), Once the slab is designed run it by your Architect to make sure that the overall heights are still correct and the slab design matches the home design. Also, a good Architect is quite practical and will be able to help iron out any services placement issues if you ask nicely, GET EVERYTHING QUOTED ON!!! - make sure that every trade involved has provided a fixed price to conduct their portion of the works. This is a curly one and we were caught out on more than one occasion by a task that no one had quoted on. This was normally followed by a conversation that usually ended with 'nah mate, we don't include that in our price, we can do it if you want to as a variation, but that's normally done by the...'. The translation is 'we didn't think of that, so now you're going to have to pay us extra' or 'we didn't tell you about that because this is where we make the money', Go and inspect people's work - everyone will tell you they do a better job than everyone else, go and see for yourself, Get referrals from associated trades - ask the tradesmen you are planning to use who they've worked with before. Generally speaking they'll remember people that have done a good job, because it makes their job easier. Getting Underway... Now that you've chosen who will do what and you're comfortable with their skill and pricing it's time to get things underway; Have the site levelled - a good tip is to think about what soil will be needed or need to be removed once you do your landscaping. It will be a lot cheaper to have the good top soil left in a pile or excess removed from site in one go, Have a Surveyor mark out the slab - it'll cost you $300 - $400, but once it's poured you can't move it, so get it done by a professional with insurance, Coordinate all of your trades so that they come to site and mark out where they need their trenches dug at the same time. This will ensure that appropriate (and legal) separation is maintained. If they refuse or are unable to come to site, at least make them draw on a scale drawing exactly where the trenches are to be dug, Once everything is marked out and has been checked by all parties, meet your slab contractor onsite and go through everything with him - generally the slab contractor will do the trenching for the other trades if you ask them to and the advantage is that they will dig out everything in the right order, so that one trade's trenches aren't accidentally backfilled by another trade as they are digging theirs, Now get your trades back on site to install their services as close as possible to the pour date to minimise any risk of vandalism or environmental damage - tip: go one size bigger than you need on all conduits / pipe work, it will only cost a little more, but it gives you the flexibility to add things at a later date that you didn't think of, for example I originally was going to have a single phase power connection, but luckily, I requested a larger conduit, which allowed a three phase connection (3 phase motors are a lot more efficient than single phase), Once all trades have completed their work and have given the go ahead (often inspections are required for underground services), have the slab contractor prepare the slab for pouring, Coordinate your Building Inspector to sign off the pre-pour inspection, Have the slab poured - note: if the slab is not flat and even you will most probably be up for additional fees from your structural trades and floor covering trades to level everything up, so make sure you're comfortable with their quality of work before you start. What we did... We have a floating slab on waffle pods Due to the nature of our design, we wanted a very large thermal mass inside our home, as insulated as possible from the outside world. To achieve this we have utilised 'Waffle Pods' on the ground, with 100mm floating slab over the top. Waffle Pods Waffle Pods are polystyrene boxes that form a void between the ground and the slab, they are used for a variety of purposes, but in our case it was to provide a thermal barrier between our house and the Earth. The most common forms of insulation (Batts, Double Glazing, Thermal Blankets, etc) work on the principal of creating stationary air pockets to prevent the transfer of heat via conduction and convection, which is why we have chosen to place our slab on top of what is essentially insulation (polystyrene) and a whole lot of air pockets. 100mm Slab Thermal Properties - to provide our home with passive heating and cooling we required a 'heat sink' that would store and release heat, helping to even out the temperatures inside. The walls are all 150mm concrete insulated with 65mm of EPS on each side (see 'The Environment' page), which gives us an enormous mass to slow down heat transference, however we also needed something that we could use to cool us in winter and heat us in summer - that's where the slab comes in. Our eaves have been designed to stop any direct sunlight hitting the slab during the hot months, so it's nice and cool, but during the winter months they allow full sunlight to enter the house and heat up the slab. This heat is built up during the day (stored in the slab) and slowly released overnight. Design - the slab is a 'floating slab', called a floating slab because it 'floats' on top of the ground with 'beams'(deeper trenches) around the perimeter to hold it in place. Because of the weight of the concrete walls, our house also has 'beams' under the walls to prevent any cracking or movement under the huge weights being sat on top of it. Finishes - our slab mix used a variety of different stone because we had the intention of polishing the slab instead of using traditional floor coverings. As it turns out, we didn't polish it, but if you did want that look, we found that Readymix were the most helpful; they offered us a variety of stone in the aggregate at no additional charge - a very big saving! You can also 'seed' the top layer of the slab as it is being poured with whatever you like (some people have used stone, pieces of glass, coins, metals, etc), once the slab has set you can have it polished and sealed (this will remove any sharp edges of items you may have 'seeded' in). This is well worth doing if you ever intend to have polished concrete (it will never be this cheap again - once it's down it's very expensive to change it). 'Seeding' is throwing handfuls of whatever on to the top surface of the concrete during the pouring process just before it is levelled out.