Normal for external air/vent grille to be below ground?

diymonkey

Thanks for your help Dave. My patio is ever so slightly sloping away from the house wall. But if I may add, the patio which is made of square concrete flags has no cement pointing between it, so the rain water goes through the flags into the ground.

Davesnave

If that's a UPVC doorway above it, the grille is at or only just below DPC; not really deep enough for ground water to penetrate unless the ground is incredibly saturated.

I had trial pits around my foundations during extreme weather one winter, and these filled up, yet I never saw the surface of the water closer than 6" off the DPC.

The cracks between the slabs make no difference. If it was bare earth, the rain would still soak in and ground water wouldn't reach the surface unless the house was built in a sump.

If the slabs were inclined towards the house, then I could imagine them channelling water to this grille, but as they're not, I'm unconvinced that an appreciable amount of water went through it.

OTOH, if you had a flash flood, as we did once in 20 years at our old house, then the slight incline of the patio might not stop water swirling around the house. Mine did, because it was built with double the slope normally recommended, so the water went past and into the neighbour''s garage....:o

But you would probably know if you had flash-flooding.

diymonkey

Much appreciate your opinion dave. In that case, what do you suggest I do? Because to be honest, I'm tearing my hair out trying to find the cause of it.

I live on a flat road which is approx 650ft above sea level. I don't understand how else I can have a flood. You mentioned that it could be the floor and now that I've looked at it, I'm thinking it might be this, because it is made of old cracked concrete which is still damp around the edges and every crack is damp.

Davesnave

In every in cellar I've known well ( a grand total of two!) the flooding has just come up through the floor.

When I was a child, we lived in a Georgian house with a shallow cellar, and the water would spread out from between the large slate floor slabs during times of prolonged heavy rain. It was never deeper than an inch or so.

Much the same happens in my daughter's Edwardian house, which is built over, or close to a spring.

I have a modern barn where the floor is about 2' below the land behind it. For around 3 winters, water sometimes spread out from a crack between two concrete floor slabs, but that's stopped happening now. Someone who's lived here a long time tells me that our springs are unpredictable like that, with ground water coming up in new places and ceasing in others. So it's possible you won't always get this problem.

It stands to reason that if the water tabler is higher than the floor, it will find its way in.

diymonkey

Davesnave wrote: »

In every in cellar I've known well ( a grand total of two!) the flooding has just come up through the floor.

When I was a child, we lived in a Georgian house with a shallow cellar, and the water would spread out from between the large slate floor slabs during times of prolonged heavy rain. It was never deeper than an inch or so.

Much the same happens in my daughter's Edwardian house, which is built over, or close to a spring.

I have a modern barn where the floor is about 2' below the land behind it. For around 3 winters, water sometimes spread out from a crack between two concrete floor slabs, but that's stopped happening now. Someone who's lived here a long time tells me that our springs are unpredictable like that, with ground water coming up in new places and ceasing in others. So it's possible you won't always get this problem.

It stands to reason that if the water tabler is higher than the floor, it will find its way in.

I plan to convert my cellar to habitable room at a later date, so would that be pointless?

Davesnave

diymonkey wrote: »

I plan to convert my cellar to habitable room at a later date, so would that be pointless?

No. Any room below ground level can be made waterproof. This is called 'tanking.'

diymonkey

Davesnave wrote: »

No. Any room below ground level can be made waterproof. This is called 'tanking.'

I'm sure tanking is a very expensive job... To save costs, can someone with some diy experience do this themselves?

Also how would tanking resolve the issue of pressured water coming through the ground?

phil24_7

Depends on the makeup of your house.

If the cellar is made of block built retaining walls then it is relatively easy to paint on a tanking slurry (I have used KE Tanking Slurry on a cellar/extension). The floors and walls (up to ground level at least unless there is designed drainage behind the retaining wall) should both be tanked at the same time to create a waterproof skin inside the cellar. You can then insulate/screed/render/plaster on top of this.

diymonkey

It's an old coal cellar and internal walls are made of bricks, so is this more difficult than blocks?

phil24_7

I think the system I used adheres to bricks, though a quick call to their technical department (who are very helpful) would confirm.