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Fwd: Location of Vapor Barrier Below Concrete Slab on Grade

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In Austarlia providing vapour barrier is mandatory in all house and
slabs on grade as specified in the code for residential slabs,
though not mandatory under factory and garage slabs on grade. However
engineers do very frequently refer to this code when designing slabs
on ground (SOG) for commercial buildings.  It makes sense because a
vapour barrier prevents moisture ingress into living areas in
addition to other advantages listed previously.  Slab on ground is 
very popular for residential buildings in Australia, espically in 
Melbourne Area.

The sequence of construction is that over a levelled natural ground 
with min. bearing pressure of 50KPa(7.25psi), a 50mm( 2in) sand bedding is
over which a 0.2mm PVC poly sheet is laid.

What surprised me is that in US, a vapour barrier is first laid and 
over which sand bedding is placed. This practice doesnot make too 
much sense to me and offcourse it creates problems described by a 
previous subscriber(extract below)

>A nagging problem up here in the Pacific Northwest with the vapor barrier is
>it usually rains (a lot lately) after the vapor barrier, sand, and rebar are
>placed but before the concrete slab is poured.  Do you take out the sand and
>start over fresh, try to dry the sand out, or punch holes in the vapor
>barrier to drain the free standing water?  Usually its holes in the vapor
>barrier due to the cost and the warranty item above.

Any comments?

Raghu S. Pendyala

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Richard Lewis, P.E.
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