Use of a second Damp Proof Membrane

[Jupiter01]

Hi,

Hope you can help me with a question relating to my floor prep. I am in the process of building an extension at the back of my house. It is a large lounge area which measures 9m x 4.7m internally.

The floor prep is as follows:
- hardcore
- sand
- 1200 gauge DPM (Taped to the membrane coming out of the walls)
- 2*100mm Celotex Insulation
- 1000 gauge DPM (belt and braces)
- steel mesh in concrete slab
- screed

Question - are there any issues with the use of the second (1000 gauge) membrane on top of the insulation? As a layman, I thought it would give me added protection against the possibility of damp rising through the concrete slab and also protect the insulation from the concrete properties.

Can you please advise on this. Thanks in advance.

 

[tony1851]

The board manufacturers actually recommend a secod sheet above the insulation to protect it from the wet concrete.
It also stops the boards floating around whilst the concrete is poured.

 

[Jupiter01]

Thanks @tony1851. I'm encouraged by your response. I've had a couple of tradesman now note that "we've never seen a second sheet", and "this will cause damp issues", etc. This has caused me some doubt and hence the post. Have you done this yourself?

 

[tony1851]

@OP, read page 8 of this, where it explains that an additional sheet should be put over the boards.

http://www.kingspaninsulation.co.uk...-4622-97bb-5861799ab02a/Thermafloor-TF70.aspx

 

[Jupiter01]

That's great. I spoke with Celotex and they suggested the same. This is compulsory according to them.
Thanks for your help pal.