# Forum Home Renovation Concreting  concrete membrane over existing garage slab for habitable / to pass council?

## Coastal

hi guys, 
council wants my garage soon to be granny flat to have a roof height of 2.4 - its currently a smigen over 2.4. the existing slab is from the '60s and does not appear to have plastic/waterproofing. I understand i need to add a membrane? 
Does anyone know of the best way with minimum thickness to make my slab worthy  :Redface: ) of council and keep the 2.4? also even if i do re-poor 1cm of concrete, what about the existing frame? is it ok to be cemented in like that? 
Anyone in umina area interested in the job? also involves 2 new slabs at either end. 
cheers
Coastal

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## ringtail

You cant lay concrete that thin, it will break just looking at it. The best way is to either get it waterproofed and tile over or get it done with epoxy products that impregnate the existing slab and seal it, then lay floor covering. You are only looking at a couple of mm either way and the slab with epoxy is virtually indestructable.

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## ozdrexler

Going through something similiar at the moment. I would be very surprised if council approves any epoxy as a solution for waterproofing the slab in a proposed habitable room. Best bet is to speak with a structural engineer of some kind, as they will have knowledge of the BCA and what is needed to get things passed through council. Might cost you a couple of $, but its money spent now that will save you heaps more in the future if you get it wrong.

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## ringtail

There are ardex epoxy products made specifically for this purpose - sealing slabs to make them habitable.

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## ozdrexler

Spoke with my local council last week about this as a solution to a slab that may not have the membrane underneath. He specifically said that liquid or epoxy type sealants are mentioned in the BCA as not being suitable or a replacement for the plastic membrane. 
His recomendation was to plastic the existing surface and then lay a new slab on top of it. Easiest, most effective and foolproof way of getting it council approved. That is also the reccomendation of a builder I consulted.  
Perhaps though it was just a recomendation to make my and thier tasks easier? how qualified and accurate are the council people?

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## Coastal

This is very interesting , what council are you with? Im with Gosford, ill call them and check tomorrow, i am going ahead with a epoxy...

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## ozdrexler

I am in Port Stephens. 
What about your height of slab above surrounding ground level? Council has stipulated my slab or floor would need to be 150mm above surrounding ground level, as per the BCA apparently.  
Its all too confusing. Surely it would be in councils interests to have a simple step by step guide for garage conversions and granny flat copnversions, something those of us not fully in the know can tick off as we go along: 
e.g. slab height 150mm or above surrounding ground floor? Concrete waterproofed? Damp Proof Course in brickwork? Minimum ceiling height of 2.4m? Sufficient airflow from windows/doors with width = ??? etc etc. You tick all this stuff as you go, and it would be  aheck of a lot easier for us who wanna learn.

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## ringtail

Hmmm, I better have a flick through my BCA then. Its all too easy for people like council to say whatever they like as it costs them nothing. Whether the epoxy is compliant or not I'm not sure, yet, but I will find out for sure.

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## ringtail

Ok, I had a good look through the BCA 2010. There is nothing mentioned in the BCA about epoxy products full stop - let alone there use as a vapour barrier substitute ( that I can find). Section 3.8.1.3 deems membranes meeting the requirements of AS4858 as been waterproof. 
Section2.2.3 Dampness - states that moisture from the greound must be prevented from causing
a - unhealthy or dangerous conditions, or loss of amenity for occupants; and
b - undue dampness or deterioration of building elements 
In SA substitute with 
Barriers installed to prevent transfer of moisture from the ground must have - 
i - high resistance to moisture penetration; and
ii - high resistance to damage during construction; and
iii - high resistance to degradation by dissolved salts 
There is the usual blurb about the thickness of the plastic sheet used etc... but the BCA makes no reference to making existing slabs habitable (that I can find). If someone knows for sure if it is in the BCA  please let us know. The bottom line is, ask the council to show you exactly where in the BCA it states that epoxy is not allowed to make a non habitable slab  habitable. I bet you they cant, in which case use a licenced person to apply the appropriate epoxy product and supply a form 15 ( for the product from the manufacturer ) and form 16 ( for the application of said product) and your golden. Like I said before, the authorities are very quick to pull the old " its against the rules" line but when asked to show the rule book they go all shy. If you have to play by the rules then so do they. The council cant just make crap up. Note that I am only referring to existing slabs here, the rules for new slabs are very clear and plastic must be used no exceptions, but for existing slabs, its one of those grey areas. I would push a little and see what happens. If you lay a new slab the ceiling height will be too low.

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## Gaza

i agree with you ringtail 100% but what about under the wall frames? if plastic dampcourse is in place then you will be right to tell council to go stick it. if not damp can rise through slab into wall's

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## ringtail

Are there walls in place now ? I dont know. Technically a garage will have walls, as opposed to a carport but ???? I agree though. However, pouring a new slab wont solve that issue unless whats there now ( if there are walls) is demolished, in which case you could lay a new slab and start again, or lever the bottom plate and epoxy under.

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