Completely full of water underneath Block & Beam floor - Damp coming through

[thefoxesmaltings]

 

We had a lot of rain recently. Something like 1 months worth in a weekend and it looks like it's filled the sub floor void.

 

We have a high water table area and the soil is firm clay, so of course that doesn't help.

 

The beams are almost completely submerged and the damp is coming through now. In the outbuilding footings, the water is right up to block level which are wet through.

 

We have telescopic vents spaced to building regs and min 150mm gap to the soil. 

 

Of course the DPM isn't down yet, and won't be for a couple of weeks. Is this okay to leave as is? I'm concerned if we get more rain, it's going to flood and come right through.

 

Should I knock out a block and pump the water out?

 

[Mr Punter]

How did the water get there?  Was it through ducting or pipes or does it just force its way out of the ground?  I would hope your floor level is much higher than external ground levels.

[thefoxesmaltings]

20 minutes ago, Mr Punter said:

How did the water get there?  Was it through ducting or pipes or does it just force its way out of the ground?  I would hope your floor level is much higher than external ground levels.

Floor level is higher than ground level, so a combination of heavy rainfall and forcing it's way out of the ground. We don't have surface water drainage in yet.

[ProDave]

55 minutes ago, thefoxesmaltings said:

Floor level is higher than ground level

Is the underside of the B&B structure higher than outside ground level?

[saveasteading]

Yes i would pump the water out. It can harm the concrete if sodden for long.

 

I would buy a cheap muck-friendly one plus hose.

 

Also, if the water level goes down and stays down, then that doesn't seem so bad.  If it appears to refill immediately from the ground then there is more concern.

 

We don't know your circumstances of course. do you have a lower area or ditch or potential soak-away to take the water to.

 

in the perfect wold you have spare land for  a pond and soak-away. then you can put in a land drain to take the groundwater away.

 

Do you have designers?  The water table level should have been considered when selecting floor level, and barriers or drains designed in.

Edited July 27, 2023 by saveasteading

[nod]

I’ve have a high water table on our previous build Our Engineer insisted I put a drain under the BB and six cube of concrete 

I thought it was overkill at the time 

[George]

Yeah I'd look at coring a drain through the wall to drain the void and getting a French drain around the house.

 

The water won't harm the building but you don't want it there.

[saveasteading]

1 minute ago, George said:

Yeah I'd look at coring a drain through the wall to drain the void and getting a French drain around the house.

A core would let water in as well as out. So maybe, maybe not

The french drain yes.   IF it has somewhere to outfall, or it might also run in reverse.

 

Plan F is to leave the sump pump in place.

[nod]

54 minutes ago, saveasteading said:

A core would let water in as well as out. So maybe, maybe not

The french drain yes.   IF it has somewhere to outfall, or it might also run in reverse.

 

Plan F is to leave the sump pump in place.

I fitted an anti flood valve to stop this happening 

It also stops rats entering the void 

Edited July 27, 2023 by nod

[saveasteading]

As you say you have clay, this will prevent rain soaking away, and it may even run across it as an impermeable surface until it reaches your permeable footings.

That would be an easy fix, in sealing the wall and cutting off the flow before it reaches.

 

Can you tell us about the slopes of the site?

 

Is the footing blockwork? It will never be watertight, but any gap in the mortar will let water pour in.

[George]

4 hours ago, saveasteading said:

A core would let water in as well as out. So maybe, maybe not

The french drain yes.   IF it has somewhere to outfall, or it might also run in reverse.

 

Plan F is to leave the sump pump in place.

I didn't mean just a hole. It'd be connected to a drain which leads downhill hopefully! 

[Dave Jones]

Need to get it out.

 

pipe it to wherever your roof water is going. 

[thefoxesmaltings]

12 hours ago, ProDave said:

Is the underside of the B&B structure higher than outside ground level?

Yes it is.

[markc]

Am I missing something here? If the outside ground is lower than the underside of the beams, how can they be submerged? That would mean the water inside is higher than the ground outside so cannot be ground water

Edited July 28, 2023 by markc

[thefoxesmaltings]

12 hours ago, saveasteading said:

Yes i would pump the water out. It can harm the concrete if sodden for long.

 

I would buy a cheap muck-friendly one plus hose.

 

Also, if the water level goes down and stays down, then that doesn't seem so bad.  If it appears to refill immediately from the ground then there is more concern.

 

We don't know your circumstances of course. do you have a lower area or ditch or potential soak-away to take the water to.

 

in the perfect wold you have spare land for  a pond and soak-away. then you can put in a land drain to take the groundwater away.

 

Do you have designers?  The water table level should have been considered when selecting floor level, and barriers or drains designed in.

 

Pumped the water out and it hasn't risen again overnight.

 

There is a ditch/watercourse which we are going to be discharging the surface water (attenuated) and foul water to.

We are actually installing a pond, funnily enough. Are you suggesting to run the perforated pipes to act as the land drain to the pond instead of the ditch/watercourse?

Our architect and structural engineer have come back also advising the perforated pipes and land drains 

 

[thefoxesmaltings]

1 minute ago, markc said:

Am I missing something here? If the outside ground is lower than the underside of the beams, how can they be submerged? That would mean the water inside is higher than the ground outside so cannot be ground water

There's no potential for it to be any other water apart from ground or rain water as the mains water is off. i.e. eliminating the chance that it is a leak. The whole site has puddles around it. It's almost as if the water is seeping in, but can't get out.

We haven't got any drainage in yet I should add, that's going to happen in a few weeks.

[saveasteading]

That's all good news then.  I think my theory of rain flowing on top of the ground then into your reservoir still     ahem....holds water.

 

So land drains it is.  Use cheap perforated pipe, gravel surround and membrane around that.

I would send it all to the pond if the levels allow, with overflow to ditch.

That way you are keeping the pond full and limiting what runs off to contribute to flooding elsewhere.