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self build problem with dpc

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#1 davestacey


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Posted 07 February 2012 - 02:43 PM

Hi all.
Having problems with NHBC. At roof level now and on my second inspector. They claim not to have any records from the first inspector who has now left them. Problem is with DPC. I had to install a gas membrane which had to go over telescopic vents on the outer wall. Because internal and external floor levels around the property are the same, it was agreed with the first inspector to put DPC one block above internal floor level. He wanted it continuous across the cavity and 150mm above finished ground level outside. The cavity tray was then at two blocks high internally and DPC level externally. This was modelled and agreed with my first inspector.
My new inspector now says DPC must be at floor level internally, but would offer no suggestions how this could be achieved and maintain the other requirements.

NHBC has just informed us that they will not do any further inspections. The trouble is we paid them to perform the local council inspections as well. I have a feeling that this could be a long process.

I offered on site to make any modifications needed but the second inspector was less than helpfull.

Does anyone know where I can go from here regarding getting some inspections done and has anyone any suggestions regarding the DPC problem?

Any help would be greatly appreciated....

#2 temp


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Posted 07 February 2012 - 03:53 PM

Have the floor slabs been done? Normally the DPM would be lapped up the walls to above the DPC before the slabs are laid. Any DPM showing on the inside is covered by skirting. Wasn't that done? My skirting is 150mm high and you could probably get higher?

Could you screed the floor or would that give major problems with the levels? (eg sand blind, another DPM this time lapped up the wall and screed on top). Not sure how much that would raise the floor levels. I think some screed is ok down to 40mm.

#3 cadmeister


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Posted 07 February 2012 - 07:06 PM

View Postdavestacey, on 07 February 2012 - 02:43 PM, said:

My new inspector now says DPC must be at floor level internally,

The inspector is wrong. How you proposed forming the tray higher on the inside leaf and at floor level on the outer leaf is a standard arrangement when detailing DPC's and radon barriers

If the DPC functions to keep damp out and the barrier funcions to keep gas out then the inspector can't argue about it

Have a look here and on page 16 is something like what you want to do

#4 temp


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Posted 08 February 2012 - 07:13 AM

As I read it he has the cavity tray and DPC are one block higher than the diagram on page 16?

Any chance of a sketch Dave?

#5 agb657


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Posted 12 February 2012 - 12:38 PM

"My new inspector now says DPC must be at floor level internally," whats the point of a DPC Higher than the floor level on the internal walls ? It seems to me the first inspector was wrong, and its always a problem when you don't get continuity of inspectors. a sketch would be useful.

#6 temp


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Posted 12 February 2012 - 08:26 PM

Thinking about the original problem again.. Wouldn't the gas membrane also act as a DPC if installed as described? That would appear to be at or below floor level. If it blocks gas will also block damp? Any DPC installed higher on the inside leaf might be un-necessary?

I'd love to see a drawing.

#7 cideredd


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Posted 19 February 2012 - 07:42 AM

Just a thought , buy a radon gas detector and take a reading in a neighbours house . You can then argue from an objective stand point . You will probably find radon isn't a problem at all , but armed with figures you can ventilate and add barriers to your hearts content.