romario

DPM / DPC overlap best practise

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I am starting first layer of blocks above DPC and I wanted to ask other people for opinion about DPM / DPC overlap best practise.

I've seen many diagrams showing the overlap but I haven't seen one peace of information of the actual best way of doing.

 

It is an internal 215mm load bearing wall.
Building control officer said to live about 50mm dpm overlap during oversite inspection.


I decided to:

Put some mortar on the blocks

Then bend on it 50mm dpm,

Then some more mortar,

Then DPC, some more mortar and blocks.
Is that the best way of doing?
 

Please see attached photo?

Am I being to cautious?

 

Thank you in advance.

DPM - DPC overlap.jpg

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When you say an internal wall do you mean the internal wall of the cavity or an actual wall inside the building. 

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1 minute ago, Declan52 said:

When you say an internal wall do you mean the internal wall of the cavity or an actual wall inside the building. 

Hi Declan,

 

I mean actual internal wall inside the building but it is load bearing on top of the footings.

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I would leave at least a 100mm of an overlap on each side. Easy to trim it back much harder to add more. 

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3 minutes ago, Declan52 said:

I would leave at least a 100mm of an overlap on each side. Easy to trim it back much harder to add more. 

Thanks Daclan for your reply.

I agree with you but I may have also confused you.

I have left more of DPM but now I am at the stage of actually laying the blocks above and I need to trim the DPM.

I am kind of trying to find the best practise in terms of how much overlap to leave when you put the mortar and also should you put the mortar between DPM and DPC.

 

I am probably to cautious but at the same time don't want to make silly mistake....

 

Thank you.

 

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Can you take a pic of how it sits at the moment.

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11 minutes ago, Declan52 said:

Can you take a pic of how it sits at the moment.

Yes, please see attached photos

215mm_width.jpg

DPM_height.jpg

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Posted (edited)
15 minutes ago, Declan52 said:

Can you take a pic of how it sits at the moment.

 

 

Yes @romarioa diagram or picture would help. I am about to do the same on my build yet I am struggling to picture what you intend to do.

 

For a conventional brick/block cavity wall construction a 200mm or more excess flap of dpc will be left on the inside wall to be tucked in with the dpm when the floor screed is added once the roof is on.

Edited by epsilonGreedy

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6 minutes ago, epsilonGreedy said:

 

Yes @romarioa diagram or picture would help. I am about to do the same on my build yet I am struggling to picture what you intend to do.

 

For a conventional brick/block cavity wall construction a 200mm or more excess flap of dpc will be left on the inside wall to be tucked in with the dpm when the floor screed is added once the roof is on.

Please see one more photo showing where I am at the moment.

The DPM, insulation and cocnrete slab has been layed down.

This is a 215mm solid internal wall.

It is kind of free standing internal square that's why structural engineer required 215mm thickness.

DPM_above_concrete.jpg

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Have been reading up some more, here is a depressing thread on another forum.

 

https://www.diynot.com/diy/threads/laying-dpc-should-this-be-on-mortar-or-not.327349/

 

In summary there is no definitive standard because those responsible skip the nitty gritty detail and builders have their own standards.

 

Having seen the awful dpc mortar bed on my own Bryant Homes built house I think the notion of brick/mortar/dpc/mortar or worse brick/mortar/dpm/mortar/dpc/mortar, is asking for trouble. Think I will adopt a welsh convention which is brick/dpm/dpc/mortar.

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27 minutes ago, epsilonGreedy said:

Have been reading up some more, here is a depressing thread on another forum.

 

https://www.diynot.com/diy/threads/laying-dpc-should-this-be-on-mortar-or-not.327349/

 

In summary there is no definitive standard because those responsible skip the nitty gritty detail and builders have their own standards.

 

Having seen the awful dpc mortar bed on my own Bryant Homes built house I think the notion of brick/mortar/dpc/mortar or worse brick/mortar/dpm/mortar/dpc/mortar, is asking for trouble. Think I will adopt a welsh convention which is brick/dpm/dpc/mortar.

 

Thank you for the link.

I am glad that is not only me who couldn't find the answer :)

 

I think I will go for:

block,

5-7mm mortar,

dpm 50mm overlap

5-7mm mortar,

dpc, 

5-7mm mortar,

block.

In my case where the wall is 215mm wide and DPC is 225mm wide it will be neater to have the DPC slighly sticking out of the wall on top of DPM ratehr than trying to squze 225mm DPC under the DPM

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@romario fold over both sides, stick a 215mm DPC on top then lay your mortar and blocks. You don’t need mortar under a DPM or DPC. 

 

If its difficult to get it to stay, use some lengths of duct tape to join both sides together and then get the DPC on top. 

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8 minutes ago, PeterW said:

You don’t need mortar under a DPM or DPC. 

 

 

Really pleased to read this confirmation, any idea what motivates the notion of mortar below dpc and/or dpm? Is it a concern the brick below might puncture the dpc?

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Posted (edited)
13 minutes ago, epsilonGreedy said:

 

Really pleased to read this confirmation, any idea what motivates the notion of mortar below dpc and/or dpm? Is it a concern the brick below might puncture the dpc?

its to avoid creating a slip plane in a masonry wall.

 

Edit: Extract from BS 8215

 

dpc.JPG

Edited by Ian
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20 minutes ago, Ian said:

its to avoid creating a slip plane in a masonry wall.

 

 

Right I now get the motivation, far more value in your single post than the other ding/dong thread between practicing brickies.

 

I guess material scientists have tested the relative friction between a dry brick/dpc joint plane and a brick/mortar/dpc joint plane.

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Just to add that the lap in a dpc should be minimum the width of the wall. So in your case-215mm wall means min 215mm lap at any join. 

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