I’ll try to keep this concise!

Our garage is part of the house, it is below the ground floor so the rear of the garage is effectively below ground, like a basement.

It floods when it rains, it’s not coming under the door (in fact the water gets trapped behind the door and can’t leak out.) Nor is it dripping down from anywhere or coming through the walls. Nor is it to do with the drains on our property, they have been checked and repaired but it still floods.

There is a “channel” around the rear and one side of the garage (inside) between the concrete slab floor and the wall, a couple of inches deep and wide. This fills up when it rains, seemingly from below then eventually overflows flooding the floor. It drains away again within 24hrs or so.

It’s like the garage is sat in a big sponge which gets saturated and that leaks in.

So it’s not the drains, United Utilities say it’s nowt to do with them, environment agency say it’s nowt to do with them, council not having it.

Who’s the expert we should approach here? A builder?

I can’t really see a satisfactory solution. If we put drainage in, The water is still there around the garage, if we tank it, The water is still there!?

Not sure how to proceed, and it feels expensive!!

Sounds like it’s occasionally below the water table. Sump and auto pump?

What’s the channel, er, made of is the best way I can describe it?

Sounds like you’ve got ground water with no place to go until the surrounding area can absorb it.

You have a few different options. Can you regrade to slope the ground away from the garage?

You could dig a v shaped trench, put a perforated drain at the bottom, running around the garage and coming out where the land slopes away, it possible. Backfill with gravel.

Put a sump pit in the back corner of the garage with a pump in it with a water level switch. Use a perforated drain in the channel you have running back to your pit, and finish over it with concrete.

There is a “channel” around the rear and one side of the garage (inside) between the concrete slab floor and the wall, a couple of inches deep and wide. This fills up when it rains, seemingly from below then eventually overflows flooding the floor. It drains away again within 24hrs or so.

Is there somewhere along the line of that channel that should be a drain and has become blocked?

Turn it into a boat shed?

What colour?

🙂

Is it a new build? If so, can you go back to the original builder?

You could tank it, but I’d try other solutions first as they’re cheaper.

Retro tanking wont work if its below actual ground water levels. The fact that there is an internal channel within the garage speaks volumes. However that’s not working correctly but it is really the only option. You need to remedy its flow and all should be good. However “its flow” is not as simple as rodding a drain, it needs to be capable of taking the maximum flow that it may receive from the surrounding run off.

Small sump, float activated sump pump, somewhere to send the water

LEave the door open and let it flow out?

Sounds like the channel is designed in for when ground water gets in, perhaps it goes to a external drain or soak-away type OR maybe there is a sump pump drain? if no pump, perhaps the old drain outlet is blocked or less efficient and hence now backs up and hence floods.
Is it an old / new house, either a surveyor or a builder could help investigate more, or we need pictures;)

Thanks for the responses so far. House built 1935, garage is a two storey extension built in the eighties (living room above the garage.)

The channel does seem to have been done on purpose as a cheap solution. I can’t figure where it should drain to though.

I think it’s always done this, but because there was so much crap in there which we’ve now got rid of combined with the new (better sealing) door we didn’t realise how bad the problem was and it’s now way worse than it ever has been (we’ve been here five years.)

I find it hard to believe that it’s been filling up with water like this for the last thirty years without some more serious problems arising

Think you’re right. Chances are there’s a drain somewhere that’s now blocked

Wrightyson – why would retro tanking not work ( I am seeking knowledge here)

My Sister lives in Amsterdamn – they dug down the lower ground floor of their building to below the water table ( so my brother in law could stand up in it) and tanked it and its been fine. During the works they had to have a pump running 24/7 to remove water

Retrofit tanking is tricky to do effectively as you are working against the hydrostatic head. New construction can be in a waterproof concrete so a bit easier or lined with a egg crate style plastic sheet and drained. Some vandex or similar waterproof screed may work short term but if there is any movement may fail again. It’s also not designed for high hydrostatic pressure.

Is there any way to drain the garage without needing a pump? That is always the preferance if feasible. Groundwater is a fickle beast and management is probably your only solution unless you can put land drainage in adjacent to the base of the garage. You may find that there were existing land drains around the base of the garage but these have now blocked with sediment washed in by that much groundwater flow.
Have you had a CCTV survey of the existing Strom drainage to prove the nextwork is clear with no pipe fractures etc. If not this would be my first point of call if you phoned my company for drainage design assistance.

Yeah we’ve had the drains camera’s. There’s one starts at the rear of the house which runs down the side of the garage and one which drops straight down next to the garage door. The both meet under the drive. They both had fractures which we’ve had repaired but that’s not affected the garage problem!

Don’t suppose you’re local to Blackpool @Van Halen!? 😜

Retrofit tanking is tricky to do effectively as you are working against the hydrostatic head.

Certainly can be done though – although probably not cost effective for this situation which, it seems, is a temporary raising of the water table probably brought about by the rather large amount of rain falling recently (location dependant).

OP, how deep is the water on the floor? If you can’t easily fix the situation you could fit some of these tiles to give you a dry surface even when the floor below is wet.
We have had them for about 10 years on a balcony at our holiday place and they’re fantastic – just clip together, strong, light and allow the surface below to drain/dry while giving a dry surface to walk on.

I suppose “flooding” is a bit over the top! It’s not like we’re wading through it.

This channel fills, then it pools in one corner and over flows and runs across the front of the garage, by the door, then flows backwards. It makes a substantial puddle!

Those tiles look a good idea, but I am concerned about just masking the problem rather than solving it.

Absolutely. Maybe you could look into creating a path for the water to exit under the door in the corner where it pools.

I’d go with the advice above re: emptying the the trench and seeing if it’s just silted up so not behaving as designed. Then worry about if you need any additional measures in place.

The channel does seem to have been done on purpose as a cheap solution. I can’t figure where it should drain to though.

Seems strange that they put in a channel but no drain at one end! Maybe it was supposed to drain out under the door.

Are we breaking the floor out when we retro tank this garage? Creating a seal at the floor/wall interface is always tricky and always will be the weak point.
As I said up there the channel was included for a reason and it needs to be capable of taking away the flow. I’d hazard a guess that the water is currently coming in at the wall/floor interface. Get a hose in there and see if you can get it running freely.

We’ve got a half-basement type annex on the side of our house (Underneath the Garage actually). the previous owners had ‘Type C’ waterproofing done as they apparently had some ingress from ground water and they ran a business out of the space, so had to get it sorted properly and permanently.

Basically the inside of the walls are lined with a membrane and then there’s hidden drainage channels below floor level with a sump and an automatic pump to carry away any water to a soakaway. Of course they’ll have taken up the floor and dug down a bit to do all of that, where I’m guessing your garage floor slab is probably a bit more permanent, and you’ll not be wanting to take it up…

Our garage is built into a hill.
It used to get an inch or so of water in the deepest part.
On the advice of FIL, I put a layer of that water seal type stuff on althe inside of all the exterior walls. Has been fine since- over fifteen years.
Worth a try for £20 or so.

What’s on the outside of the garage wall where the channel is? If it’s outdoor, I might think about digging a sump below garage floor level and either connect it to a drain or a soakaway. The existence of the channel suggests to me that the builder didn’t want to tank it, maybe didn’t want to build up a head of water against the wall. Or the tanking didn’t work…