Rainwater Ingress Via Front Door?

[b0ng0]

The Problem

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 below so I suspect the water is between the plastic and concrete, hence the carpets still dry:

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.

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.

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).

 

[blup]

I would be tempted to remove the flooring in one area and trace its source, relying on a sloshing sound may not be enough. Are there any buried pipes that may be leaking? Is the source from the garage/room 3 where the issue seems to be worse.

Blup

 

[b0ng0]

I would be tempted to remove the flooring in one area and trace its source, relying on a sloshing sound may not be enough. Are there any buried pipes that may be leaking? Is the source from the garage/room 3 where the issue seems to be worse.

Blup

The issue with removing the flooring is that it's glued down and completely flush, so it would be a huge (and expensive) job to start removing it.

No buried pipes as far as I'm aware and issue only occurs after heavy rain.

Garage is bone dry (and at a lower level than where the water can be heard). I should have clarified in the schematic - the water only gets to room 3 after extended periods of heavy rain. Smaller, shorter periods of rain it only gets to the front door/room 1. Which is why I'm currently thinking it's getting in from the front.

 

[blup]

If it is not pipes or drains (current or historic) it is possible that the water is finding its way under the front door over the dpm, the land seems to slope towards it.

Blup

 

[b0ng0]

If it is not pipes or drains (current or historic) it is possible that the water is finding its way under the front door over the dpm, the land seems to slope towards it.

Blup

That could be it - the only point where the DPM is exposed appears to be at the front door. Not sure why it would suddenly start collecting water (was fine for the first few years).

I can't 100% rule out pipes, but given the recent age of the property and the fact it only occurs during heavy rain I feel like that's less likely.

 

[b0ng0]

I took some more closeups after a brief dry period to inspect the DPC and see how the concrete is drying out. Seems a bit uneven on the left image with a damp/greenish patch right at the top.

On the right image, looks like a bit of concrete has fallen away and the DPC is sticking out - do you think that this could be collecting rain water and channeling it in?

Also the DPC seems to not go across the front door and stop at the sides? Not sure if this is normal.