Is it OK to intsall clay airbrick above DPC level?

[James]

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.

[Phil L]

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.

[dg]

SNIP

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

dg

[Phil L]

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

[John Rumm]

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

[Phil L]

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 bollocks, 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)

[dg]

Thats what the airbricks are for ;-)

dg

[James]

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.

[Cicero]

======================== 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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[Phil L]

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

[Phil L]

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

[M2006]

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.

[manatbandq]

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

[Phil L]

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