Advice pls on floor screed over block and beam flooring

[bandekk]

Hi,

I have an area of approx 6m by 3m on a ground floor extension which is block and beam construction, that I now need to insulate and screed to finished floor height. I was planning on putting 1200g DPM down, then 80mm celotex insulation (taped at joints), then 65mm screed (approx 1.2m3). After searching this forum, I found the following link referencing screed/DPM processs which mentions a Vapour Control Layer (http://www.sheffins.co.uk/pa_guide/Ground-Floor-Solutions.pdf) may also be required ? How can I confirm this.

Also I was planning on putting the DPM under the internal block work, then lapping this up the inside of the cavity and tucking back in the block work two courses up. This has been agreed with by building control. However should I lay one course of blocks first then tuck the DPM into the cavity, or is it ok to go straight under the blocks. Does it really matter anyway?

thanks

 

[freddiemercurystwin]

The VPL is just stopping the screed seeping into the insulation joints, belt an braces really. Your dpc position is fine, here's one I did earlier..............

Untitled

• freddiemercurystwin
• 25 Apr 2010
• 2

 

[bandekk]

ok great thanks.

Does your diagram show some sort of DPC tray between the 2 cavities? Its just that I've already built the first few courses of the outside wall with a DPC and wasnt expecting the bridge the cavity?

 

[bandekk]

Also whilst I think if it, I do have wall ties low down, that would pierce the DPM lapped up, should I remove these?

 

[freddiemercurystwin]

Its pretty standard to have a stepped dpc across the cavity. Any water that penetrates the outer skin runs down the the inner face of the outer skin, when it hits the stepped dpc it finds its way out of the weepholes or that's the theory anyway. As long as your Building Inspector isn't demanding one you'll probably be ok. In Radon affected areas its essential as it acts as the Radon barrier.

Also whilst I think if it, I do have wall ties low down, that would pierce the DPM lapped up, should I remove these?

Not sure I follow.

 

[bandekk]

ah that would explain the weep vents I put in, but dont have the step. BC aren't asking for it so hopefully I can leave it. (I sometimes think they havent a clue anyway).

As for the wall ties, I plan to put some ties on the 1st course of blocks, but as the DPM laps back into the blocks on the second course, the 1st course wall ties would be in the way....if you follow.

thanks

 

[freddiemercurystwin]

ah that would explain the weep vents I put in, but dont have the step. BC aren't asking for it so hopefully I can leave it. (I sometimes think they havent a clue anyway).

As for the wall ties, I plan to put some ties on the 1st course of blocks, but as the DPM laps back into the blocks on the second course, the 1st course wall ties would be in the way....if you follow.

thanks

Ah, I miss-read your post, thought it said tiles not ties hence my stupid confusion! Anyhoo my detail is slightly misguiding in that my courses aren't drawn particularly well and I would expect the builder to set the wall ties/blockwork coursing out in such a way as to miss out the two courses of block out where the dpm laps up the inner skin ie ties immediately above and below. Wall ties need to go at 450 vertical centres, sometimes an extra row is required if the courses don't work out particularly well or haven't been planned in advance.