Best solution when you have a musty and wet crawl space?

29 Aug 2019
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United Kingdom
Hello all!

First time poster:

I have a semi-detached house in a high water table area and I noticed that under the suspended wooden ground floor there was some standing water. I carried out some investigation and it appears that more water flows into the crawl space (approx 4ft high) in when it rains. The water flows in from either the rear of the house or the wall shared with the neighbours.

I will be looking to address the water coming in from the garden from the outside, as a separate project but I have come to the conclusion that I cannot 100% guarantee that water can be prevented from entering the crawl space ... though I can manage it. So I have undergone a project where I have taken off the floorboards for the entire ground floor, treated and protected the joists, and installed a sump pump.

As the floor of the crawl space is still moist and does give off a musty smell (confirmed with the water company that it's not sewage), I have put down 100mm of gravel and will be laying down and sealing a DPM over it. There are five air bricks which will be converted to the plastic type as I understand they all for better airflow but I am keen to ensure:

- The subfloor is insulated and long lasting
- No (or very little) moisture and smell rises and creeps into the living area

So my questions are:

1. Should I use 100mm celotex (rigid?) insulation which is equivalent to the height of the joists?
2. Should I lay a DPM on top of the joists before putting down the timber floorboards?

I've read other posts which are usually referenced when people have questions about the above but I don't think there are any threads which provide an answer to my particular situation

Appreciate any support you can provide!
Last edited:
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Might be worth digging a sump at the lowest point sealed to the dpm you are putting in and installing a sump pump with access via a trapdoor.
Thanks, @footprints - it was a bit of work but I installed the sump pump by digging down at the lowest point. Luckily the lowest point is under the hallway so I can install a trap door under the staircase.

Do you have any view on the insulation and DPM on top of the joists?
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