# Forum More Stuff Owner Builders Forum  Help for our concrete slabs!!

## Balicinta

Hi, 
Our house has an internal slab and an external slab that meet and are the same height. Our certifier has told us that we need to either remove the external slab or raise our internal slab as there should have been at least a 25mm step between the two slabs (so that water cannot enter between the plates). (Our certifier has suggested the following: The external Slab must be a minimum of 25mm lower then the internal slab of your house, you could do this by removing the external slab so you achieve your 100mm visual barrier which would also achieve part of your termite barrier) 
Since neither of these suggestions seem feasible (at the moment at least!) due to cost, we are trying to look at some 'alternative solutions'. The first we have proposed is that we cut approx. 200mm concrete of the external slab where it meets the internal slab and place a drainage system in. The drainage must be able to show exposed slab for the termite protection visual barrier though). 
Another person told us that we may be able to roof this section to get around it? (although that would not help us with the termite barrier). 
Another thought was to cut the 200mm out and leave it, but I would assume there would be something in the building code that would prevent us from leaving it as described. 
Any thoughts would greatly be appreciated as I have no knowledge of the building code and seem to be getting mixed answers from the BSA/council. 
Cheers!

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## woodchip

Hi, 
What type of termite protection do you have? 
Was there a stuff-up with the external slab height? 
Does the external slab slope away from the building?, if it does surely the drain would be a waste of money, or could be set down the required depth so you get the visual on termite barrier as you say. 
cheers

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## ringtail

I actually thought you needed 100 mm between slab heights. This is the norm for garages that have a entry into the house and all the slab on ground houses that Ive had anything to do with. I must admit I havent had a look through the BCA regarding the issue but it certainly is the done thing in Brisbane at least. With as little as 25 mm you may aswell have them level

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## woodchip

Gday ringtail, 
I did a waffle pod slab on flat ground some years ago that had a 1 brick (86mm) step down into garage from internal access to it. 
However I have just had a strip footing & infill slab engineered, with no step down into garage area from internal access (2x bedrooms, bathroom & laundry on same level).
I also havent looked at BCA on it, left it to the engineer. 
cheers

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## ringtail

Ok. BCA states - 25 mm slope over the first metre in *low rainfall intensity areas* or 50 mm in any other case. 
For* slab on ground dwellings* 
100 mm in *low rainfall intensity areas* or
50 mm if concrete ( impermeable) *and it must slope away as per the above* or
150 mm in any other case   *So, if you had 50 mm set down and the outside slab sloped away from the house slab 50 mm in 1 mt you would be ok. For termite you need at least 75 mm exposed edge of the house slab - unless the two slabs were poured as 1 monolithic slab or termimesh has been chased into the house slab before the outside slab was poured. Given that you live in Brisbane ( from memory), you have a serious issue. Rip it up and start over. * Thesefigures do not take into account the sewer and gully trap height clearances from the lowest sanitary fixture ( floor waste) either. 
Nearly forgot to mention that nothing has changed since you asked the same questions a year ago

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