DPM?

[junglejim]

Slowly progressing with my timber frame build and getting ready to lay dpm, add pir, ufh and screed.

 

 I’ve got a couple of questions:

1. My architect drawing shows flow dpm sealed to dpm under sole plate and lapped up external walls. (Red and blue lines in drawing) The internal walls were all installed at the same time as the external walls.  So where these intersect I can’t fold up the dpm. The easiest solution would seem to be not to fold up the dpm strips that are under the sole plate and instead fold them down but tape / seal the new floor dpm to all junctions with overlap so that can fold up. It would mean that the there is only one layer of dom above the upstand rather than the 2 in the architect spec. In the corners presumably I’d use ‘hospital bed style’ to neatly tuck in without any break in the dpm.

 

2. there are sections of the slab that to my untrained eye seem quite uneven. I can chisel off small lumps but wondering if I should be taking  additional measures to perfect the dpm? I haven’t got any photos yet and i could well be overthinking it! I don’t think self levelling screed will work because it would interfere with the dom under internal walls. I guess I’m wondering when I should worry about this and what solutions there are? I’m thinking the addition of a rubber layer (say 1-2mm) might be useful?

 

3. also with insulating the slab. The architect drawing shows the perimeter strip sitting on top of the sheet insulation. I’ve also seen lots of people do the strip first at full height then add the sheets. Wondering what the logic is for each method?

 

 Thanks as always does the help given.

[JohnMo]

5 minutes ago, junglejim said:

3. also with insulating the slab. The architect drawing shows the perimeter strip sitting on top of the sheet insulation. I’ve also seen lots of people do the strip first at full height then add the sheets. Wondering what the logic is for each method?

Each method works, but I did perimeter insulation at full depth of insulation and screed, my thoughts were less chance of a thermal bridge due to gaps. I used 70mm PIR which was the maximum use for my wall build-up instead of the normal blue stripes.

 

8 minutes ago, junglejim said:

there are sections of the slab that to my untrained eye seem quite uneven. I can chisel off small lumps but wondering if I should be taking  additional measures to perfect the dpm?

You could add a thin layer of sand or use thin eps insulation as a sacrificial layer below the DPM.

 

 

[junglejim]

Here’s some photos of the slab…any thoughts?

 

 I’m thinking of laying a geotextile to protect dpm. What do you think? 

[Big Jimbo]

That looks rough as IMO. A thin layer of EPS before you put the membrane down would do the job.

[junglejim]

On 01/11/2025 at 17:43, junglejim said:

Slowly progressing with my timber frame build and getting ready to lay dpm, add pir, ufh and screed.

 

 I’ve got a couple of questions:

1. My architect drawing shows flow dpm sealed to dpm under sole plate and lapped up external walls. (Red and blue lines in drawing) The internal walls were all installed at the same time as the external walls.  So where these intersect I can’t fold up the dpm. The easiest solution would seem to be not to fold up the dpm strips that are under the sole plate and instead fold them down but tape / seal the new floor dpm to all junctions with overlap so that can fold up. It would mean that the there is only one layer of dom above the upstand rather than the 2 in the architect spec. In the corners presumably I’d use ‘hospital bed style’ to neatly tuck in without any break in the dpm.

 

2. there are sections of the slab that to my untrained eye seem quite uneven. I can chisel off small lumps but wondering if I should be taking  additional measures to perfect the dpm? I haven’t got any photos yet and i could well be overthinking it! I don’t think self levelling screed will work because it would interfere with the dom under internal walls. I guess I’m wondering when I should worry about this and what solutions there are? I’m thinking the addition of a rubber layer (say 1-2mm) might be useful?

 

3. also with insulating the slab. The architect drawing shows the perimeter strip sitting on top of the sheet insulation. I’ve also seen lots of people do the strip first at full height then add the sheets. Wondering what the logic is for each method?

 

 Thanks as always does the help given.

Just resurrecting this in the hope someone can advise on my first point? Ta

[Mike]

I'm not clear on exactly what you mean - or rather that at a junction of an internal wall and external wall I can't envisage a problem, which probably means I've not understood you question. However any DPM / DPC is likely to be too thick to fold into hospital corners. There are pre-formed DPC corners on the market, for a price, that may help. But the fundamental rules are that all DPM and DPC junctions must overlap by at least 100mm and be to the satisfaction of your BCO.