Small.amount of water under subfloor

Faz123 · Post by **Faz123** » Wed Jun 17, 2020 9:02 pm

Hi there ,

I can really do with some advice , it has really been bugging me!!

After the heavy rain yesterday, I noticed and small area of water under my subfloor ( muddy/clay texture), today morning thankfully it had naturally drained a little.

Outside pavings are higher than my subfloor .

also had new plastic air vents put in and dpc around my timbers.

The space between the floor and ground is around 60 cm
Is there any thing I can do to keep the water levels down ?

I was thinking of adding more stone chipping?

Someone-Else · Post by **Someone-Else** » Wed Jun 17, 2020 9:09 pm

Heavy rain would cause the local water table to rise, adding chippings just hides the water.
I would not worry too much, but do keep an eye on it when it rains a lot or for a long time.
The ultimate solution has to be you build a sump* and put a sump pump into it and discharge the water down the drain.

*There is more to building a sump than just digging a hole.

Faz123 · Post by **Faz123** » Wed Jun 17, 2020 9:14 pm

Many thanks for your reply.

Will have to keep an eye on this , I think it might be too late to have a pump , just had new floor in :(

Other than a pump are there any other possible solutions?

Someone-Else · Post by **Someone-Else** » Wed Jun 17, 2020 10:19 pm

If it's too late for a pump, how did you know the water is there?

I do not know of any other solutions, but that does not mean there are none. But bear in mind anything you "cover" it with just stops you from seeing what is happening.

Faz123 · Post by **Faz123** » Wed Jun 17, 2020 10:23 pm

I've got a access point for my subfloor so was able to check.

I understand where your coming from in terms of covering it up. I thought putting some chippings down could help keep it the water down when rises

Surveyorman · Post by **Surveyorman** » Wed Jun 17, 2020 10:31 pm

I assume all your sub-floor ventilation is in place and unobscured? You should be aiming to have 9 x 3 air bricks running Running at 0.9m intervals and or 9 x 6 air bricks at 1.5m intervals, this is mainly to keep your sub-floor timbers dry and free from any build up of condensation.

If you are just getting freestanding moisture coming up through the oversite as the result of a rise in the water table, this is not necessarily an issue providing that the moisture is not affecting any of the sub-floor timbers. If you’re able to take a moisture reading from any of the timbers that would be useful. You are aiming to have a WMC (Wood Moisture Content) reading of below 14%.

Faz123 · Post by **Faz123** » Wed Jun 17, 2020 10:54 pm

Many thanks for commemting, I will definately check this out

Surveyorman · Post by **Surveyorman** » Thu Jun 18, 2020 7:13 am

No problem - let us know your findings. A photo of the outside is always helpful too

Rorschach · Post by **Rorschach** » Thu Jun 18, 2020 7:31 am

Since you have an easy access point it seems I would dig down and see how high the water table really is. This would let you know if it is a natural rise and something you can't stop or runoff coming from another area of the property (such as your patio) that could be stopped.

Faz123 · Post by **Faz123** » Thu Jun 18, 2020 7:50 am

How far down do i need to dig down ?

Chippo1 · Post by **Chippo1** » Thu Jun 18, 2020 7:53 am

I have this under the block and beam flooring of bungalow , the main thing is that there is no damp path up into the floor structure and woodwork in your case , as said local water table may rise on occasion causing some puddling.

Generally the top of soil under my floor is 300mm down from under side of the concrete beams, how ever when I dug up the screed int the kitchen and lounge I found three areas of evidence of damp on the blocks. Broke out a few blocks and found the builders in 1990 had dumped by accident or design rubbish under the floor which was touching the floor, the rubbish was mainly clay/soil Cleared out problem solved. Both floors and the hall now have a 1000 gauge DPM under the insulation and UFH

Rorschach · Post by **Rorschach** » Thu Jun 18, 2020 9:58 am

Faz123 wrote: ↑Thu Jun 18, 2020 7:50 am How far down do i need to dig down ?

You would wait until after you have had a few dry days in a row and then dig until you hit water basically. Once you reach the water table the soil would be completely saturated with water as opposed to just damp and you would likely get a puddle start to form.

If you reached this level within a couple of feet then you know the rain is just causing the level to rise a bit, if you go down further than that then it would indicate you have a surface water runoff problem.

The hole doesn't need to be very wide. An auger would be best if you have the facility to get one in.

Faz123 · Post by **Faz123** » Thu Jun 18, 2020 11:21 am

Will get to this once is dries up soon

wes56 · Post by **wes56** » Fri Jun 19, 2020 5:08 pm

Faz123, rain soaks into the ground and raises the water table.
Are you are on a hillside?
Is there a retaining wall close by?
I'd guess that its a swollen water table issue. If so neither digging nor pumping is of any use. Neither is spreading stone.
As suggested, lots of through and cross ventilation might be the best that can be done.

To help control condensation membranes (DPM's) can be spread across the sub-soil but they can end up floating for short periods when the water is high.

Faz123 · Post by **Faz123** » Fri Jun 19, 2020 8:33 pm

Surveyorman wrote: ↑Thu Jun 18, 2020 7:13 am No problem - let us know your findings. A photo of the outside is always helpful too

Hi folks , many thanks for your all your responses!

I've taken a reading of my suspended floor timbers its 17.5% , and unfortunately the humidity levels around RH 85%.

The water pools mainly near my kitchen wall which has a concrete subfloor ( previous owner had a small extension)

Also my subfloor is fairly new , its has dpc on the ends but C14 graded (should have used treated?)

I've attached some pics