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Finished floor level and DPC - can they bridge?


 
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larrylamb11

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PostPosted: Thu Jul 15, 2010 4:07 pm Reply with quote

Quick question, for various reasons it looks like we need to increase the thickness of the floor on the oversight in our extension. Originally it was going to be 150mm - 100mm cellotex board with 50mm screed.
It now looks like it will be nearer 172mm + the thickness of floor tiles - 20mm Newton membrane, 50mm insulation board, 2mm DPM, 25mm cellotex board, 75mm screed (to take pipes and UFH).
Whilst there is enough head room, the finished level of the floor will be above the DPC in the inner leaf by 10mm or so..... is that a problem? The damp proofing specialist we just had in was sucking air through his teeth which has made me wonder!
In fact because we are planning to put in water UFH we will be insulating around the edge of the screed as per normal practice so the screed slab won't touch the walls... if that makes any difference.
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theoldun

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PostPosted: Thu Jul 15, 2010 7:14 pm Reply with quote

Is this the same floor with a different design now that was posted 10 days ago.
oldun.
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simonjay

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PostPosted: Thu Jul 15, 2010 10:33 pm Reply with quote

larrylamb11 wrote:
Quick question, for various reasons it looks like we need to increase the thickness of the floor on the oversight in our extension. Originally it was going to be 150mm - 100mm cellotex board with 50mm screed.
It now looks like it will be nearer 172mm + the thickness of floor tiles - 20mm Newton membrane, 50mm insulation board, 2mm DPM, 25mm cellotex board, 75mm screed (to take pipes and UFH).
Whilst there is enough head room, the finished level of the floor will be above the DPC in the inner leaf by 10mm or so..... is that a problem? The damp proofing specialist we just had in was sucking air through his teeth which has made me wonder!
In fact because we are planning to put in water UFH we will be insulating around the edge of the screed as per normal practice so the screed slab won't touch the walls... if that makes any difference.


It doesn't matter. If you look at a diagram, you can see that everything above and inside the DPM and DPC (which should be continuous) is in the "dry" zone. You are not bridging anything, since the wet inner leaf below the DPC is separated from the screed by the vertical part of the DPM.
Its is quite usual to have this situation, or if the finished floor level is a bit lower, some of the vertical DPM exposed. This would be covered by the skirting boards etc.
The FFL usually finishes up "near" the internal DPC icon_wink.gif
Simon.
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larrylamb11

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PostPosted: Fri Jul 16, 2010 7:23 am Reply with quote

theoldun wrote:
Is this the same floor with a different design now that was posted 10 days ago.
oldun.

Yes, this is the same floor, same design as previously posted to get over this potential water ingress problem. This has increased the thickness of the layers on top of the oversite from the 150mm in the original plans (100mm cellotex board with 50mm screed) to nearer 175mm (20mm Newton 520 membrane, 50mm waterproof insulation, 2mm Newton DPM, 25mm cellotex board, 75mm screed) ..... which brings the finished floor level from just below to above the DPC in the inner leaf. We hadn't really thought it could be a problem as hopefully everything inside is now 'sealed' from any water ingress, but it was just the comments made by the damp proofing guys when they arrived on site to start laying the membranes that have had me wondering.

simonjay wrote:
It doesn't matter. If you look at a diagram, you can see that everything above and inside the DPM and DPC (which should be continuous) is in the "dry" zone. You are not bridging anything, since the wet inner leaf below the DPC is separated from the screed by the vertical part of the DPM.
Its is quite usual to have this situation, or if the finished floor level is a bit lower, some of the vertical DPM exposed. This would be covered by the skirting boards etc.
The FFL usually finishes up "near" the internal DPC
Simon.

Looking at it logically, that is kinda what I thought - doesn't sound like it will be a problem then. I will double check there aren't any potential areas where there could be a bridge and go from there.
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theoldun

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PostPosted: Fri Jul 16, 2010 2:50 pm Reply with quote

Not trying to throw a spanner into works, but would bring to your attention.
Simon is right in what he says, if this had been a straight forward over site.
However all your problems have stemmed from the fact that the vertical upstand of your DPC was damaged and failed., consequently you have no protection round perimeter. Perimeter insulation will not provide protection against damp ingress.
IMO Newton 501 should have been taken up the walls to above dpc level.
oldun
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larrylamb11

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PostPosted: Fri Jul 16, 2010 8:17 pm Reply with quote

I see what you mean..... The damproofers have lapped their new DPM up the walls a little, right up to the original DPC and bonded onto the original DPM with butile tape up to the DPC, so it looks like they have covered over any of the original breaches.
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