Suspended wooden floor causing high humidity.

[Sismithin]

Hi folks
I have a 1900 era cottage style end of terrace house.
The front living room is a suspended wooden floor. Beneath it is about a 1 meter void.
I keep getting really high humidity in the room sometimes 70+% at 16-20C
I bought a dehumidifier and leave it running all night to get the humidity down to 55ish % but turn it off and close the door and leave the house all day humidity will quickly shoot back up.

I believe the moisture is coming from the ground below the void.

I have read about putting down plastic sheeting to help matters, but my problem is the room has laminate flooring on top of hard wood and then all the skirting built onto power of the laminate along with a cast iron rad and fireplace, so taking the floor up is virtually a no no.

Is there another option I could look at. Possibly taking out bricks from down the side to enter the space or is this just stupid?
Any practical advice really appreciated.
Last winter I had quite a bit of mould on the soft furnishings and don't want the new sofa to go the same this winter.

As you can see I have a total of 5 unblocked air vents and good ventilation in the room itself with an open fireplace and trickle vents in the windows which I hoped would help

Cheers


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[ree]

1. In you pics i notice that:
- the front ground level has been raised about 5 courses but its well below the DPC line.
- black "bitumen paint" has been applied to the gable wall.
- a channel/French drain (?) has been dug at the gable.
- an injected DPC has been drilled.
- you do have metal air vents but they wont be supplying much ventilation. Totally out of character 9" x 6" plastic air bricks provide the best ventilation.

All these are previous remedial attempts to deal with damp or damp & condensation.

2. Do you have solid walls ?
Is there a solid floor at the rear of the house?
Do you have a C/H radiator in the front room?
Any signs of damp on the walls?

3. There might be an access trap to the sub-area hidden in a closet or under the stairs. But if not then one should be cut in an out of the way place - you need access to a sub-area.
Dont cut an access thro the brickwork.

 

[jeds]

How many air bricks do you have at the rear and do they communicate properly with the ones at the front - i.e. providing cross ventilation. You have air bricks on the side and front but this would not be as good as front to back. Also, can you get access to the floor void. If so I'd check the moisture content of the timbers and the humidity below floor.

 

[Sismithin]

Thanks for your response guys.
Yes it seems the previous owners have made some attempts to remedy some sort of damp problem.
The problem is the rear room is the kitchen and that is a concrete floor along with the hallway so the vents are just the 3 on the front and the 2 on the side so there is no real through airflow especially since the wind generally blow diagonally across the back.
There was a sort of French drain but this has no be routed completely away to the front and away.

They are all solid walls yes
I do have a large cast iron rad in the room
Last year I did see a damp patch in the corner of both outside walls about 4 foot up from the floor which I assume was condensation. The rest of the furniture had mild spores over it, which did reduce after I got the dehumidifier.
There is no hatch to access the space and lifting the boards will be a horribly messy task because of the laminate floor then the fibre boards and the skirting board that had been placed on top of the laminate floor, making lifting then difficult.
I'm certain the moisture/humidity is coming the from exposed earth beneath, what else could I consider. Compared to the kitchen the humidity is really high and stays high.
What else could I look into apart from constantly running the dehumidifier which I don't really want to do as it won't solve the underlying problem?
Thanks guys

 

[ree]

For your hallway to be a solid floor means that the hallway was filled up to 1m.
Is the understairs also concreted over?
Do you know if there is a membrane (DPM) below the hall concrete?

The only suspended floor that you now have is the front room lounge? Is that the case?

A joiner or joinery skilled floorperson could easily locate a safe area & cut & trim an access trap without causing the upset you fear.

Or, failing that, then open up the side wall brickwork for an underfloor inspection, and any remedial work to take place eg. a moisture barrier over the oversite. Its possible that heavy humidity & faint ventilation in the crawl space could damage the joists.
On completion of work re-brick the opening back up.

A constant trickle of heat, some say 13C, and constant through ventilation can help with managing condensation.

Its a possibility that moisture is penetrating thro the render and solid walls but without firmer evidence it would need a site inspection.

What did the survey report when you bought the house? Was a damp & timber report issued?

 

[jeds]

You really need to get a proper look at the sub-floor. If it is not ventilating correctly, apart from causing the problems you are experiencing, it could cause damage to timbers. Do you have no vents at all on the rear walls? You say the rear floor is concrete but the correct method would be to duct vents through the concrete. Is that a good floor or one you could cut a few ducts into?

 

[Sismithin]

The hallways is a solid floor along with the kitchen to the rear which are the two room surrounding the living room in question. Both kitchen and hallway do have a plastic DPC.
Because of the depth of the kitchen and then conservatory putting a bent through would be almost impossible I imagine.

Nothing was brought up on the inspection, it wasn't the best at all to be honest.

It's my fear that the timbers are going to be suffering too...what a pain all this is.
I'm slowly learning the quirks and problems a period property bring, this being a high up the list.
I think knocking a hole in the side is the only way really, I think it's time to get some sort of specialist in.
Would filling in the majority of the void with cement be an option? Providing a solid base and hopefully stopping any moisture rising up?

Cheers

 

[jeds]

The hallways is a solid floor along with the kitchen to the rear which are the two room surrounding the living room in question. Both kitchen and hallway do have a plastic DPC.
Because of the depth of the kitchen and then conservatory putting a bent through would be almost impossible I imagine.

Nothing was brought up on the inspection, it wasn't the best at all to be honest.

It's my fear that the timbers are going to be suffering too...what a pain all this is.
I'm slowly learning the quirks and problems a period property bring, this being a high up the list.
I think knocking a hole in the side is the only way really, I think it's time to get some sort of specialist in.
Would filling in the majority of the void with cement be an option? Providing a solid base and hopefully stopping any moisture rising up?

Cheers

Not really sure what you mean by filling the majority of the void with cement. Converting the floor to solid construction would solve the issue if done properly but you would need specialist advice to make sure this doesn't cause problems elsewhere and I'm pretty sure that option would cost a lot more than cutting vents across your existing rear floors - if that is what is required. I'd get a local chartered surveyor to have a look and advise you. Make sure they have experience of dampness issues and period construction. The only problem is it is going to be difficult to advise fully without some sort of access beneath your suspended floor.

 

[Joe Malone]

Cheers[/QUOTE]
Converting the floor to solid construction would solve the issue if done properly but you would need specialist advice to make sure this doesn't cause problems elsewhere [/QUOTE]

It would never solve the problem and in fact would drive moisture into the wall base under hydrostatic pressure.