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Dpm as dpc

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#1 albyt1


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Posted 21 June 2010 - 10:18 PM

Hi All

I am new here and have a question that might seem silly, why do we have to have a dpc and dpm on inner walls, why not just dpm as this will stop damp rising

#2 laurence


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Posted 22 June 2010 - 09:58 PM

I think the dpm material is capable of being pierced by hard materials (that's why you have a sand blinding course between the dpm and the hardcore). The dpc material is thicker. They overlap in the walls to ensure continuity at the join but it is the dpc that is the essential barrier in the walls.

#3 albyt1


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Posted 26 June 2010 - 09:14 AM

My question was a little vauge, so I will enlarge.
When a Dpm is put in, it is normally tied into the Dpc course on the inner wall, sandwiched between courses and Dpc with mortar, in this case why not just use Dpm and omit th Dpc as Dpm will serve both purposes. I hope that is a little clearer.
In reply to Laurence (thanks for reply)
Dpc and Dpm are normally sandwiched with mortar on bricks/blocks, so Dpm would not get pierced by any hard material in this case, I have been researching this, and so far the best reason it is not used in the way I have layed out is that Dpm is plastic and will cause a slip plain, whilst Dpc is keyed for his purpose, but as I have all ready said they are normally tied in together so there would still be a slip plain.

My thinking is that it can be used in this way and that putting both Dpm and Dpc in is a throwback, if any one knows of a good reason why this is not the case (apart from required by Building Control) please let me know

#4 temp


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Posted 26 June 2010 - 11:58 AM

Perhaps DPM might not be strong enough where there are voids? I know you are meant to fully fill the frog before placing the DPC but perhaps that's not allways good enough to avoid the DPC being pushed/stretched into voids by the load above?

I've also seen references to "high load DPC". I thought this might be for retaining walls but the instructions said it wasn't to be used for that.

#5 builders


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Posted 26 June 2010 - 12:34 PM

There is no reason to use a dpc on the inner wall as long as you have over lapped the dpm from your over site onto the inside skin of the wall. The only place we would put the dpc on the inner wall is where the new wall meets the old building this is where we put the dpc 150mm into the old buildings damp course we then roll it out about 1m into the new wall and let the oversight dpm do the rest of the damp proofing. I hope this answers your question. http://www.cuttingedgecarpentry.biz

#6 mentalmicky



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Posted 28 July 2010 - 05:18 PM

Why fuss about it ? for a fiver a roll- may as well put it in and keep everyone happy !!.
But- theres always someone who cant conform !!