Really high humidity in WC

[JP_]

Got a strange issue. In my bathroom (which is really just a WC as the bath is rarely used) the humidity is really high.

It started to smell a bit damp after I put laminate floor down in the hallway. Then spotted condensation forming on the legs of a cabinet in the WC.
Currently, the room does not have skirting board along one wall.

Humidity reading was 84% the other day. I reduced it with dehumidifier to about 50, but it has risen again. Window vents open.
The hallway and kitchen stay a steady 50-55% humidity.
No
All drainage in the room goes straight out the wall, and water pipes were replaced. The floor was up for a while and no leaks.

Could the issue be because there is no skirting board? Maybe water vapour just condensing because it's the last cold spot?
I shoved some towels and bits of insulation where the skirting should be, and that seemed to help a bit but humidity has risen to 77 again today. Nobody home, no showers, cooking etc. Just one small dog breathing.

There was a little sign of damp on the concrete sub floor along the outside wall - could this be a cause? Odd, as it has been so dry recently. I did dig a French style drainage channel down the side of the house a few years ago, but did not get to this part of the house as there is a gate and manhole, so left it. But might have to dig more.

Any suggestions?

Will add photos in a minute, from my phone.

 

[blup]

Its a small room with a cold external wall and limited air circulation.

Blup

 

[JP_]

The external wall has 50mm Kingspan + insulated 10mm tilebacker board, so cold wall should not be a problem. The room stays warm, new rad, very hot! Has new window too, and the vent has been open. Also extractor fan that comes on when the light is switched on, with overrun.

 

[blup]

I can only say from experience of badly fitted double glazing (in terms of sealing around the new frame) that cold will find its way in with a vengeance at the weakest spots insulation wise.

Blup

 

[JP_]

Probably the lack of skirting boards then, the window is well fitted, no gaps. Also no bath panel on at the moment, and some gaps under there to the sub floor. Will shove in more insulation.

Leaving the door open lowers humidity pretty well. This morning it was 16C / 81% on the window sill.

 

[foxhole]

Have you placed you humidity “gauge” next to each other to confirm their accuracy .?

 

[JP_]

Yeah, they are pretty consistent. And the dehumidifier's gauge matched too.

 

[JP_]

I will seal up with skirting boards asap and see how that goes.
Should I fill that gap along the bottom with some foam, to reduce condensation risk along the bottom?

 

[bernardgreen]

It started to smell a bit damp after I put laminate floor down in the hallway.

Did this humidity problem start or become noticeable after the laminate floor has been laid ?

If so then did the laminate floor block an existing ventilation gap under the door to the room ?

 

[JP_]

There's still a fair gap under the floor. I've ordered skirting board, will seal it up and then assess from there.
Unless there's a leak on the sub floor sending up huge amounts of water vapour, it must be condensation.
My assumption is that the old exposed wooden floors absorbed moisture, and now we have laminate, there is more in the air. As well as fewer cold spots. If skirting boards don't work, I'll dig more outside. If that doesn't work, I'll have to try to inspect the sub floor, without disturbing the new flooring!

 

[Odds]

You say the new radiator is very hot: can it be turned down at all to help reduce condensation?
It sounds like the radiator is kicking out more heat than the window vent can handle.

 

[JP_]

I might have a hot water leak....
Wall looked at today, and plasterboard feels wet, not just surface condensation. And, both sides of the wall (brick) feel wet, and feels warmer than it should...

And, recently the hot water taps started acting like they're was an air lock, spluttering.

And humidity higher here than in window sill.

Is there a way to know for sure without ripping up my new floor? Maybe call home insurance?

 

[JP_]

Both of these humidity readers are giving similar results when together, humidity usually same, temperature a degree different.

Here there are each side of the open door. Left is 64, right is 81. Hall is 50 on the wall.

 

[JP_]

This morning the humidity sensor died, it was full of water. I think we can rule out condensation now.

 

[Odds]

You need a plumber, old spout, not a dehumidifier.
Bad luck.