Rainwater Ingress Under Floors? Damp can be a major issue in the home. Find answers to questions or post your own here.

[b0ng0]

The Problem
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I've got an issue whereby water is getting into my house whenever there is moderate-heavy rain. This is a new build from 2015 (maybe that's not so new now...)

I suspect it is coming in via the front door, but there is no visual evidence of water ingress anywhere - however, walking around there is a very audible sloshing under the floors. But the flooring itself (including carpets) is bone dry.

I've tried calling a few damp specialists but without visual evidence of water they can't do much. The original builder (big national company) doesn't want to hear it as it's out of warranty. NAHB won't look into it without visual water damage - so I'm on my own for now!

The Pictures

The construction of the flooring is (bottom up):

Concrete
Plastic Membrane
Plywood
Laminate

I've tried to make a schematic below of where the water can be heard in the house. I think it enters at the front and then is just pooling at low points. The heavier the rain, the further into the house the sloshing can be heard.

schem.PNG (52.35 KiB) Viewed 970 times

I've investigated for cracks, poor/broken sealant, any way the water can get in but can't find any. I removed the blocks at the threshold and concrete is still intact with no obvious damage or cracks.

If I move aside some of the gravel at the side, there is some plastic membrane you can just about see.

rightzoom.PNG (208.16 KiB) Viewed 970 times

The garage (white door on left) which is at a lower level than the front door is completely bone dry, even during heavy rain. There is no pooling of water on the lockblock either. Everything is very level (build to wheelchair standards).

[stoneyboy]

Hi bongo,
Suggest you rule out the possibility of a high water table. Dig holes either side of your front path, say 18” deep and see if water collects.
Regards S

[stoneyboy]

Hi bongo,
Suggest you rule out the possibility of a high water table. Dig holes either side of your front path, say 18” deep and see if water collects.
Regards S

[b0ng0]

Thanks for the suggestion, will try that and see - not sure if I can get down that far but at least should give a visual indication.

However, the garage is at a lower level and is completely dry so I would have thought that would be the first place to experience issues if the ground water level was rising during rain. The rear of the house is also completely unaffected.

The picture below is the DPC(?) sticking out. Possible that water is collecting on that and being channeled on top of the membrane?

On the left side the DPC is folded down, although at the top still looks a bit wet/greenish whereas directly under looks dry?

[stoneyboy]

Hi b0ng0,
The fact that the sloshing gets further into your house when it rains heavily links the issue to rainwater ingress.
It’s likely that your floor construction is block and beam with a membrane directly below the top layer of the floor covering - probably a screed. If you are saying that you can hear squelching when you walk across the floor then it is likely that there is some defect with the construction in the front door area.
You must eliminate the possibility that ground water rises in the front door area. If this is not the case it could be that the DPM has been taken under the front door allowing water to be fed into the house. The question is where does the water go once it is under your floor screed?
Regards S

[b0ng0]

I have some holes dug near the front door, just need to wait for next rain. However the rain is getting in, it must be getting out the same way as it drains away.

Maybe I should get a joiner to look at the front door threshold, or speak with the original flooring company and get them to take a look?

[stoneyboy]

Hi b0ng0,
Arm yourself with as much investigative results before you call in others.
Do you know what your floor construction is eg concrete screed plus soft or hard covering; chipboard plus soft or hard covering. Either way these layers above the DPM could be adsorbing the water.
Regards S

[b0ng0]

I have tried to get information from Cala (the builders) but they fob me off everytime saying they've changed their flooring design and all the guys associated with my house build have moved on...

I do have building plans from an extension we had built (which doesn't have the water issue) and they tried to keep the flooring design the same as the house.

It consists of (top to bottom)

Laminate flooring
22mm Chipboard
50mm Recitcel Eurothane (insulation)
125mm concrete slab with 1 layer A193 mesh top 30mm cover
100mm Recitcel Eurothane (insulation)
1200 gauge DPM
50mm sand blinding
Foundations

If the rest of the house is the same as the extension then I feel like the water must be in the concrete slab and/or 100mm insulation. So either DPM has a hole in it, or water is getting in over the top.

I have checked the drains leading away from the property, all water levels way below ground level. Checked the downpipes and all look in tact and leading away from the property.

Not sure if water could be getting in between the walls? In that case I would expect to see water damage on the walls?

[stoneyboy]

Hi b0ng0,
Gosh that a really difficult situation.
If you main house floor construction was the same as your extension it very unlikely that you would be able to get the squelching feature due to the 125mm thick floor slab.
Your house must have had building regulations approval so can you find out if detail plans were submitted? If yes you may be able to get the flooring detail from there.
Regards S

[b0ng0]

Following up with new info.

Discovered rainwater has been entering under the floor via the phoneline/broadband duct. The green box is at a higher elevation and the duct didn't have either sufficient drainage or wasn't sealed properly when the property was built meaning it filled up and then was able to escape into the house.

The duct has recently been isolated but there remains the issue of potential damp from water that is still there (there's a few holes cut in the floor so I can see that the concrete is still damp to the touch as are some timbers). The only solution I can think of is to take up all the flooring, get some industrial dehumidifiers and run them until it dries out - not ideal and expensive.

NHBC have rejected the claim as it doesn't fall within their policy as the issue isn't caused by a structural defect and the water source is external. My own insurance says it falls under additional "accidental damage" which I don't have on my policy - but I don't see this as accidental damage this is a fundamental problem with the development of the house not due to some accident cause by us or otherwise.

My question is - who should ultimately be responsible for rectifying this type of issue? Given that:

• - the source of water is rainwater
  - the ingress point was in a duct external to the boundary of the property which allowed water to flow in
  - the duct design came from BT/Openreach but was installed by a subcontractor to the builder (large national company)

It seems like no one wants to take responsibility and leaves us with possible damage and an very expensive problem to fix. Is it ultimately on the builder to make it right? After all, they were responsible for subcontracting the installation of the duct and making sure it was carried out correctly.

Appreciate any advice!

[stoneyboy]

Hi b0ng0,
Thank you for the update, as you say the solution is to remove the floor layers back to the concrete floor slab.
Since you are in a modern build and have not mentioned damp up internal walls, it is very likely internal wall are of stud construction, so these will also have to be removed of suspended.
If you are going to pursue anybody involved in the build you will need a report from a building professional identifying the problem. You will then have to engage a legal person to identify who is responsible and probably follow up with court action.
I’m sorry to tell you that it’s very likely that carrying out corrective works yourself may well be the cheapest and only solution.
Regards S