My wife's sister lives in a detached 1968 house in Hasting, Sussex. Its built on the side of a hill. The hill is pretty steep so the back of the house is
3M below the front and it then has a patio and steps and the garden 2M below low that. The house is only half as deep downstairs as upstairs, following the hill shape.
The lounge is at the back of the house and you go down stairs to get to it. She has started to see white mold under the stairs down to he lounge and as there is a trap door under the stairs I had a look under the floor. The ground below the lounge floor is about 1M below and dry and flat with various floor supporting walls with access points to get around.
There are underfloor vents at the side but the patio has blocked the vents at the back of the house.
Near one of the side walls there are two pits, about 1M wide and 2M long and 1.5M deep and these are wet filled with about 25mm of water. The underneath of the lounge floor is covered in white fury mould, though not the joists. I assume this is due to the high humidity under the floor and wondered what can be done to fix this.

The first thing you need to do is get the ventilation right. It is possible to have the air vents below ground level but you need to fit pipes large enough not to obstruct air flow and at the top the pipes need to be angled and have angled louvres on the ends to prevent water ingress. However this not your only problem as if the patio level is above the vents it will also be above any damp course level. You will need to excavate a trench along the patio/wall interface below the the air vents by about two bricks you can then put gravel in to act as a French drain, ideally with some means of draining away although for a short bout of rain it will simply drain into the soil.

As for the rot wet rot is the easier to deal with cut away any rotten timber and replace. Dry rot is the bigger problem if it has tendrils spreading across the timber then that is dry rot and you need to cut back all affected timber at least 600mm past the furthest extent of the rot. What remains must be treated including any brickwork in the vicinity to kill off any spores. To be honest it is a specialised job and I would recommend you get a company in to identify the rot and if need be treat it.

Richard

Thanks,
What do you think should be done with these pits in the sub floor, which I assume are going down to the water table as they are wet. Would filling them reduce the humidity.
On Monday, 18 November 2019 14:57:45 UTC, Tricky Dicky wrote:
The first thing you need to do is get the ventilation right. It is possible to have the air vents below ground level but you need to fit pipes large enough not to obstruct air flow and at the top the pipes need to be angled and have angled louvres on the ends to prevent water ingress. However this not your only problem as if the patio level is above the vents it will also be above any damp course level. You will need to excavate a trench along the patio/wall interface below the the air vents by about two bricks you can then put gravel in to act as a French drain, ideally with some means of draining away although for a short bout of rain it will simply drain into the soil.

As for the rot wet rot is the easier to deal with cut away any rotten timber and replace. Dry rot is the bigger problem if it has tendrils spreading across the timber then that is dry rot and you need to cut back all affected timber at least 600mm past the furthest extent of the rot. What remains must be treated including any brickwork in the vicinity to kill off any spores. To be honest it is a specialised job and I would recommend you get a company in to identify the rot and if need be treat it.

Richard

I have never heard of something like this before, but I am aware of houses built on slopes with rooms on different levels having voids. These are not intended as living space and often are not tall enough to be used as anything more than storage although an uncle of a friend of mine built a model railway in one.

If the house had previous owners I would suspect one tried to create an extra room but gave up once his excavations started to fill with water and you may be right that the water is the source of the damp conditions encouraging mould. I would fill up the holes with gravel put a blinding layer of sand on top on top of which I would cover the whole area with a damp proof membrane finishing of with a 100mm layer of concrete. That should seal the dampness but you still need to ensure adequate ventilation.

Richard

On 18/11/2019 15:19, Steve J wrote:
Thanks, What do you think should be done with these pits in the sub
floor, which I assume are going down to the water table as they are
wet. Would filling them reduce the humidity.

Hard to say. They may be deliberate sumps to drain water out of the
cellar. One way would be to make a sump with a submersible pump and a
float switch so that any water that accumulates gets pumped out.

Don't delay if it is dry rot it moves at a fair clip and when you make
conditions drier so that it feels threatened it will create fruiting
bodies. Various sites have images of what wet and dry rot looks like.

It is confusing though as there are loads of wood rot fungi but only a
few of them are seriously damaging to structural wood. You may need an
expert to take a look at it to recommend the best remedial treatment.

The chemicals required to kill and prevent reinfection are not DIY.

Regards,
Martin Brown


On Monday, 18 November
2019 14:57:45 UTC, Tricky Dicky wrote:
The first thing you need to do is get the ventilation right. It is
possible to have the air vents below ground level but you need to
fit pipes large enough not to obstruct air flow and at the top the
pipes need to be angled and have angled louvres on the ends to
prevent water ingress. However this not your only problem as if the
patio level is above the vents it will also be above any damp
course level. You will need to excavate a trench along the
patio/wall interface below the the air vents by about two bricks
you can then put gravel in to act as a French drain, ideally with
some means of draining away although for a short bout of rain it
will simply drain into the soil.

As for the rot wet rot is the easier to deal with cut away any
rotten timber and replace. Dry rot is the bigger problem if it has
tendrils spreading across the timber then that is dry rot and you
need to cut back all affected timber at least 600mm past the
furthest extent of the rot. What remains must be treated including
any brickwork in the vicinity to kill off any spores. To be honest
it is a specialised job and I would recommend you get a company in
to identify the rot and if need be treat it.

Richard

There are some wet rots with tendrils too (not the most common).

--
Regards,
Martin Brown

On 18/11/2019 12:34, Steve J wrote:
There are underfloor vents at the side but the patio has blocked the vents at the back of the house.

And that could well be the cause of the problem.

Whoever built the patio should have buried 4 inch drainage
pipes to connect the existing vents back to the outside ,
allowing crossflow of air.

On Tuesday, 19 November 2019 15:26:10 UTC, Andrew wrote:
On 18/11/2019 12:34, Steve J wrote:
There are underfloor vents at the side but the patio has blocked the vents at the back of the house.

And that could well be the cause of the problem.

Whoever built the patio should have buried 4 inch drainage
pipes to connect the existing vents back to the outside ,
allowing crossflow of air.

The mold is white and fury and round and does not seem to have damaged the floor yet see https://inspectapedia.com/mold/Subfl...d135-DJFss.jpg

On 19/11/2019 16:51, Steve J wrote:
On Tuesday, 19 November 2019 15:26:10 UTC, Andrew wrote:
On 18/11/2019 12:34, Steve J wrote:
There are underfloor vents at the side but the patio has blocked
the vents at the back of the house.

And that could well be the cause of the problem.

Whoever built the patio should have buried 4 inch drainage pipes to
connect the existing vents back to the outside , allowing crossflow
of air.

The mold is white and fury and round and does not seem to have
damaged the floor yet see
https://inspectapedia.com/mold/Subfl...d135-DJFss.jpg

That looks like surface mould rather than anything else, but it is as
well to wear a decent face mask when working in there. The spores of
some damp moulds are potentially nasty lung infections.

https://www.nhs.uk/conditions/Aspergillosis/

And although that source says you have to be immune suppressed or
otherwise vulnerable I known of apparently healthy adults affected.

--
Regards,
Martin Brown