Basement/Garden Room - how damp is too damp?

shortcrust

I live on a steep hill and my 'basement' is two rooms, the front is below ground level and damp but the rear is slightly above ground level and leads to the garden. It's used for storage and isn't visibly damp. The humidity in the rear room is around 80% (let's assume it's accurate - I know the caveats about humidity meters). It's got amazing potential and I'm thinking of converting it to a garden room but on a very limited budget. Is 80% too high to be sticking a sofa, book case, TV etc?

tizzle6560

whilst I'm no expert, from previous experience with damp, an ideal reading would be 45-55%. IMO 80% sounds a bit too Amazonian rainforest for books and sofas etc.

Ozzuk

At 80% I think you'll need a dehumidifier running pretty much constantly (and fixed drain) or anything you'll put in there will covered in mold. That seems pretty high!

Had a quick google, http://www.criticalcactus.com/ideal-home-humidity-levels/

80% is a haven for mites, that would be enough to put me off. Perhaps there are air flow solutions you could look at.

martinsurrey

Ozzuk wrote: »

At 80% I think you'll need a dehumidifier running pretty much constantly (and fixed drain) or anything you'll put in there will covered in mold. That seems pretty high!

Had a quick google, http://www.criticalcactus.com/ideal-home-humidity-levels/

80% is a haven for mites, that would be enough to put me off. Perhaps there are air flow solutions you could look at.

OP, what temperature is the room when you took those readings?

Those are Relative humidity readings (relative to max capacity of the air, which is related to the temperature).

For example if you took a room of 80% humidity air at 10 degrees c and raised the temperature to 22 degrees c, the relative humidity would drop to 37.9%

shortcrust

Thanks for the replies - I thought this thread has sunk without trace!

It's currently 16C and 72%, which is pretty low for the room, perhaps because I've had the heating on for an hour today for the first time since I started using the meter. It was around 80% during the hot weather when the room reached 20C+.

The things stored down there don't seem to fare too badly. For example, cardboard doesn't have mold and nothing's rusty. I keep firewood down there and that's been ok. However outdoor chair cushions etc have that 'outdoor fabric' smell that every sun lounger seems to end up with when stored in garages etc. I don't know if that's how a sofa would end up. There's not much more I could do in terms of ventilation.

I might pop garden type furniture in rather than living room stuff and see how it goes. I already spend quite a bit of time down there on wicker furniture as it gets lots of late afternoon/evening sun. The mites thing is a real turn off though.

martinsurrey

shortcrust wrote: »

Thanks for the replies - I thought this thread has sunk without trace!

It's currently 16C and 72%, which is pretty low for the room, perhaps because I've had the heating on for an hour today for the first time since I started using the meter. It was around 80% during the hot weather when the room reached 20C+.

That's not good. 72% 16 degree air has a dew point of 11 degrees, which means at night you will get condensation.

do you know if the below ground wall has had any tanking done?

shortcrust

martinsurrey wrote: »

That's not good. 72% 16 degree air has a dew point of 11 degrees, which means at night you will get condensation.

do you know if the below ground wall has had any tanking done?

None of it has been tanked. Can you just tank a single wall? There's really just the one wall that's underground and it seems like all the damp comes from there.

There's condensation in the front part of the basement, particularly under some of the piping. I'll have a look at insulating them if that would help? There's no real sign of condensation in the back/garden room bit. It's heated when it's cold and warmish in summer so it probably doesn't get below around 11C that frequently.

I imagine that I'll eventually get some serious work done - the neighbours have transformed their basements - but am keen to enjoy the space as much as possible in the meantime.

shortcrust

Thought I'd resurrect this thread to share my excitement. The council gave a us a lovely new pavement last week which goes right up to the front of my house. Over the past view days since then the humidity has steadily dropped to around 55%, and the wall that's been constantly damp to the touch since I moved in is now dry. I'm guessing the old surface was allowing water to get in somehow.

Hooray!:) Am keeping everything crossed that it's not a temporary coincidence (with the weather and all...).