3 Blocks to Damp Proof Level - 2 Blocks internal

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Wolverine

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Hi Guys - Need some advice please.

My builder is supposed to do 3 blocks to Damp Proof Level.
All external / Cavity walls are done 3, but he has only done 2 courses on all internal walls.

I rang him to ask why - and he said that he'll fill the whole internal space with filling/blinding, lay radon barrier, Aeroboard, and Concrete up the the level of the 3 course exernal walls.

I was under the impression that all internal walls should go up 3 blocks also ?


Does anyone know if there was anything wrong with doing the above ?
Is it the norm ? Or is he cutting corners ?

Thanks,
Furious D.
 
If I understand your senario, then what he is doing is common. If the internal walls were also up to three blocks it makes it very hard to lay the radon barrier properly ( it has to go up and over the internal blocks ) and is liable to get torn.

Its much better to lay it flat and then put the third block on top, then pour the concrete.

Regarding the outer (cavity walls) what is normally done is the inner leaf is up to three blocks (your finished floor level) but the outer leaf is left at two blocks and the barrier goes over both then the third row is put on the outer leaf.

Damp proof course is then put on top of the third row.

Hope this makes sense (but probably clear as mud!)

Homebond do a great book on best practices and specifiactions, it should be available in Easons. (Homebond House Building Manual, McCarthy, Farrel & McFeely)
[broken link removed]
 
Last edited:
Hi Dusty - Thanks a million for the reply.


You're right about the external leave as such - Not too worried about that as such.

Can you advise on the following.


when he fills and blinds, and as you say layes radon barrier as one across the whole internal space, will he only do it up to the level of the top of block 2 ? see example below

is block 3 layed ontop of insulation board, ontop of few inches of filling, or is it layed on the radon barrier, on block 2 ?

...............| Block 3
...............- Radon Barrier
filling........| Block 2 (internal)
filling........| Block 1 (internal)

I just don't understand where the insulation board and concrete comes into it ?

I'm afraid that I'll end up with the internal walls built on 4 inches on contrete, on 4 inches of Aeroboard, on a few inches of filler, on the 2 internal blocks.
To me this seems wrong for load bearing walls. Surely there should be no weight on the aeroboard ?

I've bought that book - but it's a bit difficult to follow if you're not in the trade.. Must have another gander...

Thanks again Dusty,
Furious D.
 
The Radon Barrier will be laid over the top of block 2 on the internal walls and the third block laid directly on top. The insulation is then laid on top of the radon barrier and the concrete poured over it. The insulation wouldn't normally pass under the internal walls.

Concrete...| Block 3
Insulation..| Block 3
...............- Radon Barrier
filling........| Block 2 (internal)
filling........| Block 1 (internal)

However:

Depending on your Plumbing he may only pour a subfloor sometimes the pipes are laid ontop of the insulation before the concrete is poured, or the floor is poured in two stages first a sub-floor (which covers the insulation but leaves room for pipes) then the finished floor at a later stage.

Finished Floor...| Block 3
Subfloor..........| Block 3
Insulation........| Block 3
.....................- Radon Barrier
filling..............| Block 2 (internal)
filling..............| Block 1 (internal)

If there are non load bearing internal walls sometimes these are built directly off the floor but these would normally be stud-partions

Hope this helps
Dusty
 
Builder,

If you are about to build a house via direct labour I strongly suggest you buy the Homebond book I mentioned in my post above and read it cover to cover, It will give you a broad understanding of best practices and specifications.

It is also a good idea to visit other houses being built (with the owners permission!) and look at how they are constructed.

Damp-proof course is a layer (usually plastic) that goes between the foundation and the walls to stop damp rising.

Cheers
Dusty
 
Dusty - Just one more.

Hi Dusty,

Can you help me with just one more question ?

The damp proof Course is a thin strip of plastic that is placed on top of top block of dpc.
am I right in saying that it's also a large sheet that covers the whole internal aswell ?


I'm confused .
Should there be two sheets of plastic covering the whole internal
the DPM and the Radon Barrier ?
Or are the just both in one ?

Thanks a million .

Furious D.
 
In areas where a Radon barrier is not required a Damp Proof Membrane is used (it is still a plastic sheeting but is much cheaper).

In your case the Radon Barrier also acts as the Damp Proof Membrane.

Have a good look at the barrier once it is fitted if it gets torn, insist that it is repaired with the appropiate tape.

Regards
Dusty
 
Hi,

If you run radon barrier over inernal wall and onto external wall can that also act as a dpc? I persume this is true as all radon barrier act as a dpm hence prevent rising damp therefore they will do the same job as a dpc on both the internal and external wall. If you were to do this and not put any dpc in place could you run into problems. Making sure to leave your path level below radon level on external wall, ensuring not to breach the radon.

Any comments??
 
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