Internal Concrete Floor Height vs DPC

[Mag2.0]

Hi

I've started a DIY garden room build, preparing for the foundations.
I will be complying with permitted development for outbuilding and there for have a maximum roof height of 2.5m.

The usual floor detail I see is DPC at 150mm above external floor level. Top of internal floor at DPC level with DPM lapped with the DPC = internal floor height 150mm above external floor height.

I want to maximum the internal height height with the 2.5m roof height in mind.

I'm proposing the attached detail, lowering the internal floor below DPC level.
Anyone see any issues with the proposal?

Any helpful comments must welcome!

 

[danfre]

Finish above floor, fixings for skirting

 

[noseall]

Anyone see any issues with the proposal?

Yes. The DPM will get damaged. Fit the DPC/DPM (lap) at floor level

 

[Mag2.0]

Yes. The DPM will get damaged. Fit the DPC/DPM (lap) at floor level

Hi Nosall,

Just for clarification, do you recommend lowering the DPC/DPM at the floor position (75mm above external floor level).

Regards

 

[noseall]

Hi Nosall,

Just for clarification, do you recommend lowering the DPC/DPM at the floor position (75mm above external floor level).

Regards

The DPM - In that location - yes. You can double damp if you wish, to prevent splash issues.

 

[^woody^]

What is the purpose of the two DPM's?

What's that line in the wall level with the screed surface?

How thick is the wall?

Presumably you are happy with a step down from the main building, and propose detailing the DPM the same up the main wall?

 

[Mag2.0]

What is the purpose of the two DPM's?

What's that line in the wall level with the screed surface?

How thick is the wall?

Presumably you are happy with a step down from the main building, and propose detailing the DPM the same up the main wall?

@^woody^
Thanks for your input, I made an error in my original proposal. New one attached. It looks much more suitable now. I don't think I require as much as the 225mm clear cavity. Perhaps just 150mm.
The threshold will be 75mm above external ground level so the DPC will be breached over the width of the door.

@noseall
Thanks. I think it makes much more sense now.

 

[^woody^]

Where the inner DPC is lower, there is a route for damp across the wall below the outer DPC.

So

 

[Mag2.0]

Hi @^woody^

Cool. Appreciate the input. An additional vertical DPM is not an issue.

Out of interest, how does the damp travel across the cavity below the external DPC level? via the insulation or other means?

Regards

 

[Mr Chibs]

Good diagram chaps, I'm curious, why is the cavity left clear, I thought a weak mix was supposed to go in below ground level?

 

[noseall]

Good diagram chaps, I'm curious, why is the cavity left clear, I thought a weak mix was supposed to go in below ground level?

Yes - lean mix cavity filled up to within 225mm of DPC. Woody being lazy after his holiday abroad.