My extension spec says the floor slab will be "50mm soft sand on
oversite as required", then DPM, 100mm polystyrene , 100mm concrete
slab etc. What does "oversite" mean ?
I read elsewhere that 6 inches of compacted hardcore is usually
required under the sand. The area to be slabbed is at present
compacted sub-soil and some areas of pea shingle around the drains. I
was going to put the sand etc onto this. Will this be OK, or do I need
to dig out 6 inches and replace with hardcore ?
Thanks,
Simon.

sm_jamieson wrote:
My extension spec says the floor slab will be "50mm soft sand on
oversite as required", then DPM, 100mm polystyrene , 100mm concrete
slab etc. What does "oversite" mean ?
I read elsewhere that 6 inches of compacted hardcore is usually
required under the sand. The area to be slabbed is at present
compacted sub-soil and some areas of pea shingle around the drains. I
was going to put the sand etc onto this. Will this be OK, or do I need
to dig out 6 inches and replace with hardcore ?
Thanks,
Simon.

Starting from the bottom:
150mm MOT (hardcore) whacked down
50mm sand blinding whacked down
125mm of polystyrene (100mm is not enough - you can use 75mm celotex but
this is often more expensive than a 75 + 50 sheet of polystyrene (they don't
make 125mm for some reason, although this is now standard))
visqueen (1200dpm)
100mm concrete.

The sand blinding is now surplus to requirements because it was originally
to stop the DPM being perforated by the MOT, but considering most people now
put the DPM *above* the polystyrene, it's not required, although the BCO
doesn't see it that way.

You can put the DPM under the insulation, but the concrete sometimes rides
underneath it and shoves it upwards.


HTH

On 11 May, 17:04, "Phil L" wrote:
sm_jamieson wrote:
My extension spec says the floor slab will be "50mm soft sand on
oversite as required", then DPM, 100mm polystyrene , 100mm concrete
slab etc. What does "oversite" mean ?
I read elsewhere that 6 inches of compacted hardcore is usually
required under the sand. The area to be slabbed is at present
compacted sub-soil and some areas of pea shingle around the drains. I
was going to put the sand etc onto this. Will this be OK, or do I need
to dig out 6 inches and replace with hardcore ?
Thanks,
Simon.

Starting from the bottom:
150mm MOT (hardcore) whacked down
50mm sand blinding whacked down
125mm of polystyrene (100mm is not enough - you can use 75mm celotex but
this is often more expensive than a 75 + 50 sheet of polystyrene (they don't
make 125mm for some reason, although this is now standard))
visqueen (1200dpm)
100mm concrete.

The sand blinding is now surplus to requirements because it was originally
to stop the DPM being perforated by the MOT, but considering most people now
put the DPM *above* the polystyrene, it's not required, although the BCO
doesn't see it that way.

You can put the DPM under the insulation, but the concrete sometimes rides
underneath it and shoves it upwards.

HTH

!00mm polystyrene is OK since I'm full plans approved before 2006.
I've checked on this.
But the 6 inches of MOT is required as far as you are aware ?
Where new drains would come within the MOT layer, how would these be
protected ?
They would have pea shingle around, but how is this separated from the
MOT, when there
is no "edge" as such ?
Simon.

sm_jamieson wrote:
!00mm polystyrene is OK since I'm full plans approved before 2006.
I've checked on this.

OK

But the 6 inches of MOT is required as far as you are aware ?

You may get away with 100mm, but yes, it is definately required.

Where new drains would come within the MOT layer, how would these be
protected ?

unless they are a few feet down (I think 2 or 3) of the slab, then they need
capping in concrete prior to the MOT going in....certainly if they are so
high that the MOT is going to touch them, they will require capping, ask
your BCO before commencing with this though as some are more picky than
others.

snip

On 11 May, 17:27, "Phil L" wrote:
sm_jamieson wrote:
!00mm polystyrene is OK since I'm full plans approved before 2006.
I've checked on this.

OK

But the 6 inches of MOT is required as far as you are aware ?

You may get away with 100mm, but yes, it is definately required.

Where new drains would come within the MOT layer, how would these be
protected ?

unless they are a few feet down (I think 2 or 3) of the slab, then they need
capping in concrete prior to the MOT going in....certainly if they are so
high that the MOT is going to touch them, they will require capping, ask
your BCO before commencing with this though as some are more picky than
others.

snip

One other thing, I have an inspection chamber penetrating the floor
slab (i.e. will be internal).
The only thing to do here will be to have a gap in the insulation I
suppose, but what do you do with the
DPM ? Just bring it up and cut off at the top ?
Simon.

sm_jamieson wrote:
On 11 May, 17:27, "Phil L" wrote:
sm_jamieson wrote:
!00mm polystyrene is OK since I'm full plans approved before 2006.
I've checked on this.

OK

But the 6 inches of MOT is required as far as you are aware ?

You may get away with 100mm, but yes, it is definately required.

Where new drains would come within the MOT layer, how would these be
protected ?

unless they are a few feet down (I think 2 or 3) of the slab, then
they need capping in concrete prior to the MOT going in....certainly
if they are so high that the MOT is going to touch them, they will
require capping, ask your BCO before commencing with this though as
some are more picky than others.

snip

One other thing, I have an inspection chamber penetrating the floor
slab (i.e. will be internal).
The only thing to do here will be to have a gap in the insulation I
suppose, but what do you do with the
DPM ? Just bring it up and cut off at the top ?
Simon.

What has the BCO said about the manhole? - I think you wil have to re-route
it so that it's outside the building, if that's possible, if it isn't
possible, then you'll have to have it inside,and as you say, cut it off at
the top.

On 11 May, 21:55, "Phil L" wrote:
sm_jamieson wrote:
On 11 May, 17:27, "Phil L" wrote:
sm_jamieson wrote:
!00mm polystyrene is OK since I'm full plans approved before 2006.
I've checked on this.

OK

But the 6 inches of MOT is required as far as you are aware ?

You may get away with 100mm, but yes, it is definately required.

Where new drains would come within the MOT layer, how would these be
protected ?

unless they are a few feet down (I think 2 or 3) of the slab, then
they need capping in concrete prior to the MOT going in....certainly
if they are so high that the MOT is going to touch them, they will
require capping, ask your BCO before commencing with this though as
some are more picky than others.

snip

One other thing, I have an inspection chamber penetrating the floor
slab (i.e. will be internal).
The only thing to do here will be to have a gap in the insulation I
suppose, but what do you do with the
DPM ? Just bring it up and cut off at the top ?
Simon.

What has the BCO said about the manhole? - I think you wil have to re-route
it so that it's outside the building, if that's possible, if it isn't
possible, then you'll have to have it inside,and as you say, cut it off at
the top.

The manhole was always part of the plans, required due to a junction
between the main
soil pipe and a new toilet. Anyway, a cut in the DPM would not form
much of an upstand,
so DPM would have to be added like a vertical cylinder, which would
serve no purpose at
all.
It looks like I'll have to contact the BCO to sort out a few of these
issues !

Simon.

sm_jamieson wrote:

The manhole was always part of the plans, required due to a junction
between the main
soil pipe and a new toilet. Anyway, a cut in the DPM would not form
much of an upstand,
so DPM would have to be added like a vertical cylinder, which would
serve no purpose at
all.
It looks like I'll have to contact the BCO to sort out a few of these
issues !

Simon.

All you need to do is cut a piece of DPM around 7ft square and place it over
the manhole, then tuck the edges in so that it's touching the sides of the
manhole, however creased it is, it will be OK.
Then lay the rest of the DPM as normal, obvioulsy the square will need
cutting out for the manhole, but the first one will stay in place,
underneath, as long as there is an overlap of a foot or two, then nothing
will get through.
Then cut out around the manhole lid once the concrete is finished

On 12 May, 00:15, "Phil L" wrote:
sm_jamieson wrote:

The manhole was always part of the plans, required due to a junction
between the main
soil pipe and a new toilet. Anyway, a cut in the DPM would not form
much of an upstand,
so DPM would have to be added like a vertical cylinder, which would
serve no purpose at
all.
It looks like I'll have to contact the BCO to sort out a few of these
issues !

Simon.

All you need to do is cut a piece of DPM around 7ft square and place it over
the manhole, then tuck the edges in so that it's touching the sides of the
manhole, however creased it is, it will be OK.
Then lay the rest of the DPM as normal, obvioulsy the square will need
cutting out for the manhole, but the first one will stay in place,
underneath, as long as there is an overlap of a foot or two, then nothing
will get through.
Then cut out around the manhole lid once the concrete is finished

OK thats great. I'll ask the BCO about the drain capping. I'll post
details back here for completeness when I know.
Thanks,
Simon.