Hello,

 

I have been doing plumbing under my floor which has required me to crawl in the under floor a lot. In there, there is some old bitumen on top of the sand. I believe its there to stop moisture coming in through the ground. Problem is, it is all broken up as black jack gets fragile over time so is no longer serving its purpose. The ground is cool damp to the touch even after being left for a couple years. There are definitely no leaks causing it, it is likely there from a previous leak that has been addressed.  I wanted to know if it is worth running a DPM over the top as i have a good bit spare of heavy gauge DPM. I was thinking running some weed fabric to protect it from punctures as there is rubble dotted about and maybe the odd screw, then run the DPM on top of it and finally adhere the DPM to the walls below the DPC by a few bricks using expanding foam. Would this be worth it? Would it help keep it dry under there and would it be OK to do so?

 

Any advice is greatly appreciated, thank you.

 

See my diagram below if needed.

Edited March 19, 20251 yr by Joshua Graham

No, it's not likely to be worth it. Just make sure that it's well ventilated with air bricks at regular intervals on two opposite walls. And preferably make the floor airtight and insulate it - there are plenty of threads on here about doing that

Mike, thanks for the reply.

 

Yes i have already done a bit of air tightening of the floor using a dpm between the floor board and joist which was taped to the plaster forming a somewhat decent air barrier. I also have 100mm PIR board between joists. Should mention another reason i would do it is to make maintenance easier and cleaner as i may need to under there a few more times and possibly again in the future also. For that alone it is worth it to me, I would also like to know if covering the area with a dpm would cause issues. It is only one room and a small room 1.8x 1.9 bathroom.