Just got the builders in doing the shell of an extension as I didn't
trust my bricklaying skills.

They've walled up to DPC level and are about to re-install the clay
airbrick and clay liner that they salvaged when they demolished part of
the old wall.

The airbrick and liner will sit on the DPC, between the joists and just
below floorboard level.

We're on a sloping site with both DPC and airbrick over two feet above
ground level, and the other existing airbricks at this side of the house
have been similarly placed above the DPC with no obvious ill effects.

I'm concerened that, technically, a clay airbrick/liner should really be
beneath the DPC as it creates a transmission route for moisture through
the cavity. Is this a real concern or is the risk negligible in
practice?

Any advice appreciated.

James wrote:
Just got the builders in doing the shell of an extension as I didn't
trust my bricklaying skills.

They've walled up to DPC level and are about to re-install the clay
airbrick and clay liner that they salvaged when they demolished part
of the old wall.

The airbrick and liner will sit on the DPC, between the joists and
just below floorboard level.

We're on a sloping site with both DPC and airbrick over two feet above
ground level, and the other existing airbricks at this side of the
house have been similarly placed above the DPC with no obvious ill
effects.

I'm concerened that, technically, a clay airbrick/liner should really
be beneath the DPC as it creates a transmission route for moisture
through the cavity. Is this a real concern or is the risk negligible
in practice?

Any advice appreciated.

negligible, or more to the point, non-existent. because this isn't the dpc
you are talking about, it is the preliminary dpc that the joists sit on,
there will be another at floor level.

Phil L wrote:
James wrote:
SNIP
negligible, or more to the point, non-existent. because this isn't the dpc
you are talking about, it is the preliminary dpc that the joists sit on,
there will be another at floor level.

No, there is only ever one DPC in the wall. A timber floor typically
has the floorboards slightly higher than the external DPC.

dg

dg wrote:
Phil L wrote:
James wrote:
SNIP
negligible, or more to the point, non-existent. because this isn't
the dpc you are talking about, it is the preliminary dpc that the
joists sit on, there will be another at floor level.

No, there is only ever one DPC in the wall. A timber floor typically
has the floorboards slightly higher than the external DPC.

dg

So the floor joists in a newbuild house or extension are below the DPC? -
modern timbers wouldn't last 12 months below ground, there is dpc below the
joists, then the joists with 2 courses of bricks, then another dpc at floor
level

Phil L wrote:

So the floor joists in a newbuild house or extension are below the DPC? -
modern timbers wouldn't last 12 months below ground, there is dpc below the
joists, then the joists with 2 courses of bricks, then another dpc at floor
level

You don't see many new builds with floor joists at all on the ground
floor do you?

--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:
Phil L wrote:

So the floor joists in a newbuild house or extension are below the
DPC? - modern timbers wouldn't last 12 months below ground, there is
dpc below the joists, then the joists with 2 courses of bricks, then
another dpc at floor level

You don't see many new builds with floor joists at all on the ground
floor do you?



No, but the OP is having one built, or an extension to one, and as he says,
the existing vents (and joists) in the house are above DPC too.

We came close to putting one in this extension we are currently doing
because the BCO wants 26 inches of infill removing, wheeras we'd normally
only take about 5 inches and the remaining 6 inches which exist below DPC on
the exisiting building would have given us 11 in - ample for 2" sand
blinding, 5" of polystyrene and 4" of concrete.
The only drawback to putting in a timber floor was that he still wants it
concreting below the joists, to 'cap off' and noxious fumes which may be in
the surrounding (industrial) area and 75mm of celotex and a minimum of 270mm
airgap and all the other related ********, so we've just decided to remove
20m3 of infill and apply 20 tonnes of MOT.
Block and beam (concrete) would have cost us over 3K, this is costing 2K and
timber even more (45m2)

Phil L wrote:
dg wrote:
Phil L wrote:
James wrote:
SNIP
negligible, or more to the point, non-existent. because this isn't
the dpc you are talking about, it is the preliminary dpc that the
joists sit on, there will be another at floor level.

No, there is only ever one DPC in the wall. A timber floor typically
has the floorboards slightly higher than the external DPC.

dg

......
modern timbers wouldn't last 12 months below ground, .....

Thats what the airbricks are for ;-)

dg

In article ,
"Phil L" wrote:


negligible, or more to the point, non-existent. because this isn't the dpc
you are talking about, it is the preliminary dpc that the joists sit on,
there will be another at floor level.


Thanks for the replies. Phil, I'm afraid you've lost me there. I've
never seen a house with more than one damp course.

"James" wrote in message
...
In article ,
"Phil L" wrote:


negligible, or more to the point, non-existent. because this isn't the dpc
you are talking about, it is the preliminary dpc that the joists sit on,
there will be another at floor level.


Thanks for the replies. Phil, I'm afraid you've lost me there. I've
never seen a house with more than one damp course.

========================
It's now common practice (especially during refurbishment) to wrap the ends of
joists in DPC material when there is a risk of penetrating damp. This might be
what he's describing. This has nothing to do with the damp course. Metal joist
hangers solve the problem.

Cic.

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Cicero wrote:
"James" wrote in message
...
In article ,
"Phil L" wrote:


negligible, or more to the point, non-existent. because this isn't
the dpc you are talking about, it is the preliminary dpc that the
joists sit on, there will be another at floor level.


Thanks for the replies. Phil, I'm afraid you've lost me there. I've
never seen a house with more than one damp course.

========================
It's now common practice (especially during refurbishment) to wrap
the ends of joists in DPC material when there is a risk of
penetrating damp. This might be what he's describing. This has
nothing to do with the damp course. Metal joist hangers solve the
problem.

Cic.

It's not a DPC as such because it's not at the correct height (floor level),
it's just a membrane laid on the course that the joists are sat on, it saves
wrapping the ends with it, the genuine DPC is at floor level

James wrote:
In article ,
"Phil L" wrote:


negligible, or more to the point, non-existent. because this isn't
the dpc you are talking about, it is the preliminary dpc that the
joists sit on, there will be another at floor level.


Thanks for the replies. Phil, I'm afraid you've lost me there. I've
never seen a house with more than one damp course.

You live in one.

You said this in your OP:
'The airbrick and liner will sit on the DPC, between the joists and just
below floorboard level.'

Ergo the dpc must go under the joists? - you can't have a DPC below the
level of your floor

In article ,
"Phil L" wrote:

Thanks for the replies. Phil, I'm afraid you've lost me there. I've
never seen a house with more than one damp course.

You live in one.

You said this in your OP:
'The airbrick and liner will sit on the DPC, between the joists and just
below floorboard level.'

Ergo the dpc must go under the joists? - you can't have a DPC below the
level of your floor



Yes, the DPC is under teh joists.

The DPC has to be below the level of the floor - there'd be no point
having one otherwise, would there?

What we've got is like this:

--------------- floorboards ---------------
x ........... x x x
x . . . . . . x x x
x . . . . . . x x x
x . . . . . . x x x
x ........... x x x
--------------------dpc--------------------

where xxx is a joist and ... is an airbrick.

On Oct 4, 4:53 pm, "Phil L" wrote:
James wrote:
In article ,
"Phil L" wrote:

negligible, or more to the point, non-existent. because this isn't
the dpc you are talking about, it is the preliminary dpc that the
joists sit on, there will be another at floor level.

Thanks for the replies. Phil, I'm afraid you've lost me there. I've
never seen a house with more than one damp course.You live in one.

You said this in your OP:
'The airbrick and liner will sit on the DPC, between the joists and just
below floorboard level.'

Ergo the dpc must go under the joists? - you can't have a DPC below the
level of your floor

Why not? It surely depends upon the relative levels of the floor and
gound outside.
If, say, the floor is 3' above ground level why can the DPC not be 1'
or 2' above ground level but below the floor level?

MBQ

wrote:
On Oct 4, 4:53 pm, "Phil L" wrote:
James wrote:
In article ,
"Phil L" wrote:

negligible, or more to the point, non-existent. because this isn't
the dpc you are talking about, it is the preliminary dpc that the
joists sit on, there will be another at floor level.

Thanks for the replies. Phil, I'm afraid you've lost me there. I've
never seen a house with more than one damp course.You live in one.

You said this in your OP:
'The airbrick and liner will sit on the DPC, between the joists and
just below floorboard level.'

Ergo the dpc must go under the joists? - you can't have a DPC below
the level of your floor

Why not? It surely depends upon the relative levels of the floor and
gound outside.
If, say, the floor is 3' above ground level why can the DPC not be 1'
or 2' above ground level but below the floor level?

MBQ


And how do you get in and out of the house if it's 2 or 3 feet above ground
level?



- steps perhaps? - and where these join onto the house they are then above
DPC level