Water under B+B floor

[crispy_wafer]

Hi all,

 

Our build is currently sitting dormant whilst we wait on the better weather to Shell and roof.  We are up to dpc with the block and beam floor down.  Our water table is quite high, we've got clay about a metre down so water seems to just sit for a while.

 

I've got water under the floor, it appears to be sitting at about the water table level, so I'm thinking that its coming through the foundation block work as well as from above.  Fortunately the b+b floor level is a fair bit higher than ground level as a condition was to have FFL higher than the existing property on site due to flood risk (Internal drainage board deep drain about 100m away).   The oversite? is about the same level as ground level outside the build I guess higher in places and lower in others.  

 

I don't really like seeing water down there, something just doesn't compute in my mind.

 

Very crude diagram attached

 

I've read about french drains around the perimeter to help move water away, but I havent really got much depth and fall to play with to a roadside drain, can I infill the oversite maintaining the ventilation gap to raise the ground level?  Any other options, If I have to I dont mind lifting/moving the floor to remediate if i have to.

 

 

 

[Big Jimbo]

It may not just be coming through the blockwork below dpc. It may also be rising to sit at the water table level. French drains around the outside may help, but only if you have somewhere lower to take the water to that has good drainage.

[George]

Did a Civil Engineer have any input into the level design? Doesn't normally for domestic but if it's a flood risk they may have in this instance.

 

What is the surface water strategy? Ideally you'd drain to a soakaway/swale/watercourse, or with permission to a surface water sewer or combined sewer. Although things get a bit weird in Inland Drainage Board areas. 

You're not allowed to connect into a highway drain and raising the oversite levels may cause issues with neighbouring properties, so I'd be careful about either of those options.

 

As for the water, if it's due to the high water table you'll not be able to shift it anyway. It shouldn't affect the foundation but you could fill any gaps that are accumulating water with type 3 stone to protect the soil from erosion.  

[crispy_wafer]

Thanks George, The Highway drain is 'my drain', were on an non public maintainable highway, the type where neighbours all band together and look after, I dug it out and maintain it and have done for the last 20 years.  I'm not worried about draining to that too much, but If I laid a pipe it would be about 2-4 inches under the existing ground level, and I bet I'd have to raise some levels as the pipe run would pass through the garden, which is a bit of a bowl.  I think infilling could be a solution, I just hate the idea of standing water inside the 4 walls, already got me waking up in the night to think about possible solutions...  However if its absorbed in stone, or some other material then I think I can deal with that.

 

The current bungalow is built on a concrete slab and FFL is about a foot out of the ground.  The water table levels haven't caused an issue for as long as we've lived in it.

 

The new build FFL will be about 2 foot out of the ground - thanks drainage board, hence the design including b+b floor.

[tonyshouse]

It is not a problem, the level will rise and fall naturally but won’t do any damage so long as it does not freeze, lots of people have it without realising it. 

[George]

38 minutes ago, crispy_wafer said:

Thanks George, The Highway drain is 'my drain', were on an non public maintainable highway, the type where neighbours all band together and look after, I dug it out and maintain it and have done for the last 20 years.  I'm not worried about draining to that too much, but If I laid a pipe it would be about 2-4 inches under the existing ground level, and I bet I'd have to raise some levels as the pipe run would pass through the garden, which is a bit of a bowl.  I think infilling could be a solution, I just hate the idea of standing water inside the 4 walls, already got me waking up in the night to think about possible solutions...  However if its absorbed in stone, or some other material then I think I can deal with that.

 

The current bungalow is built on a concrete slab and FFL is about a foot out of the ground.  The water table levels haven't caused an issue for as long as we've lived in it.

 

The new build FFL will be about 2 foot out of the ground - thanks drainage board, hence the design including b+b floor.

 

It's within the footprint but outside the moisture (DPM) and thermal (insulation) envelope. 

 

And if the IDB's pumps break you might be thankful for the extra clearance...!

[crispy_wafer]

31 minutes ago, tonyshouse said:

It is not a problem, the level will rise and fall naturally but won’t do any damage so long as it does not freeze, lots of people have it without realising it. 

 

I think the problem here, is now I've seen it, I cant unsee it ?, just need to get my head around it being part of the 'character' ...  ?

[Andehh]

I just created a thread with exactly the same worry, in exactly the same scenario. 

 

Did you ever resolve it, or just accepting it?,

[crispy_wafer]

Hey, yes... I saw your thread, so I'll reply there for you.