Damp Oversite - should I be worried about this?

[Gizzydash]

Hi All,

Doing some work on floors and a particular room is giving me a bit of stress. One room I've lifted the floorboards in and the oversite is dry, dusty to touch. Another room at back of house (pic attached is a different story). It's patchy at best, with some areas apparently dry and you can see from the pictures one side of the sleeper wall is noticeably damper (moisture meter flashing above it's 2% max for stone/brick etc).
There is one air brick in bottom left of the floor plan picture which is open and air flowing. I've run a dehumidifier in the room for quite a while now, windows open, been no rain now for quite a bit and it doesn't appear to be drying up. The outside walls of the room have few hairline cracks in the render and there's a downpipe on the corner (where airbrick is) but some investigations around this show it's not leaking.
The top left of the room on the picture, behind that wall is a radiator with pipes under concrete and not too far away is the hot water cylinder, again with couple of pipes running out, assume towards that radiator.
Could it just be the case of water soaking up from the ground below and there's nothing I can really do about it or should I be exploring further for a leak somewhere?

Thanks

 

[blup]

My two pennyworth as diyer.

There may be a missing or failed dpm under the oversite but the localised damp suggests a more recent problem

Check the buried pipes and re route above floor level if possible. That will be cheaper than digging up and replacing the floor with new dpm and finding the problem is still there. Short of that isolate the joists from the source of the damp by using offcuts of dpm. Additional air bricks should improve ventilation.

Blup

 

[Gizzydash]

Thanks. Missing/failed DPM crossed my mind - a builder I had out suggested drilling out a sample of the floor to see what's going on but I'm not too convinced on that plan. I had thought it was potentially just poor ventilation, with just one air brick in the corner and the other blocked off by a later extension, but I'd expected it to have dried out a month after the floorboards have been up. However, maybe it takes a really really long time to dry out.
Other than that I've got my pressurised heating losing 1/2 bar over 5-6 weeks, assume that wouldn't be enough water to cause damp like this, but still needs checking, and close by hot water cylinder and power shower chased into wall could be culprits. Fear I probably need some leak detection specialist to rule out any potential leaks.

 

[^woody^]

There may be a missing or failed dpm under the oversite

I would hope so. There should not be any DPM under oversite

 

[^woody^]

The whole point of a ventilated, suspended timber ground floor with oversite is that the oversite stops any vegetation growth, the timber is protected from getting damp and air bricks ventilate the void.

There may well be some dampness to the oversite and that is not a defect, but standing water, especially below only some rooms, would suggest a leak from a drain or supply pipe, or a poor drainage issue externally.

 

[Gizzydash]

Thanks Woody - appreciate there may be some dampness but with adequate ventilation this isn't really an issue. No standing water thankfully even after some thunderstorms a few weeks back that put down an awful lot of water in a short space of time. I think I'll rule out any pipe leaks nearby, ensure drainage etc at the outside walls is 100%, stick another airbrick in to account for the one that was covered up by a previous owner and that's about all I can do really.

 

[blup]

I would hope so. There should not be any DPM under oversite

Not likely historically, the point being made was that damp in the concrete could have caused the existing joists to rot.

I don't know if any modern housing uses suspended floors but suspect building control would require a suitable dpm in such cases.

Blup

 

[stuart45]

Suspended timber floors are rare in new build houses, although often used on extensions. The oversite requires no DPM, but the top should ideally be above ground level, or a drainage system installed.
There has to be a min of 150mm from oversite to bottom of joists.

 

[^woody^]

Not likely historically

Totally likely, historically, contemporaryily, and futurally.