1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Condensation despite low humidity?

Discussion in 'General DIY' started by Deerhound, 22 Jul 2020.

  1. Deerhound

    Deerhound

    Joined:
    1 Mar 2016
    Messages:
    17
    Thanks Received:
    0
    Country:
    United Kingdom
    I've had a bad smell in my upstairs front bedroom for perhaps a year.

    It comes on overnight. After rain it's a damp, almost mildewy smell. When it's dry it's more musty.

    It seems mainly to come from around floor level in the back corner of the room. One wall in that corner is a party wall and the other is internal to my house - i.e. it's nowhere near any possible source of water ingress. The roof is fine. I've had the floorboards up and the subfloor timbers are all bone dry. No plumbing in the area. The neighbours on the other side of the wall don't have any problems. The smell is also also quite strong on the other side of the back wall of the room, from the floor inside a fitted cupboard. I occasionally get a damp smell on my stairs outside the room too.

    A protimeter showed some dampness (16%ish) in the bricks behind the skirting board in the smelliest areas. But some bricks in the same areas measure 0%. There's no dampness measurable on the plaster anywhere in the room and the skirting board itself wasn't damp.

    It sounds like a straightforward case of condensation. However, a hygrometer left next to the bricks overnight shows maximum humidity is normally 40-50%, occasionally almost 60% but never higher, and the temperature never gets anywhere near the dew point. Several windows are left open in the room every night, year round.

    I've had two independent damp people out to look, who thought the damp readings in the bricks were probably caused by salts rather than moisture. One treated one patch of "damp" bricks with a salt treatment. However, the smelliest area is very to access as it's right at the point where one wall meets another, in a small cavity above where a beam sits in the party wall. There's also a joist running 1-2 inches away from the smelly wall which makes most of the bricks in the area hard to reach. I probably can't lift that joist without damaging the old lath ceiling it's attached to.

    A structural engineer I had out last week to look at another problem (don't ask) suggested that hygroscopic salts on the bricks were causing condensation to happen at much higher temperatures than the normal dew point. Does that sound right?

    He recommended sealing the bricks to stop damp air reaching them.

    Specifically:
    1. Where the bricks are accessible, seal with a silicone based solution than cover with an anti-salt treatment to be sure. Alternatively, just pin a plastic sheet over them.
    2. Where bricks are inaccessible, fill the area with insulating spray-foam.

    To treat this I'm going to have to rip out a fitted cupboard. The spray-foam in particular is also hard to undo so I'm keen to get a second opinion on whether this all sounds like a good idea before going ahead.

    Any views hugely appreciated!
     
  2. Sponsored Links
  3. foxhole

    foxhole

    Joined:
    14 Mar 2006
    Messages:
    16,230
    Thanks Received:
    1,817
    Location:
    Kent
    Country:
    United Kingdom
    Any pics of exterior?
    Damp companies tend to be totally unqualified chancers .
    Structural engineer is the wrong person to be asking , not their field of expertise.
     
  4. Deerhound

    Deerhound

    Joined:
    1 Mar 2016
    Messages:
    17
    Thanks Received:
    0
    Country:
    United Kingdom
    Thanks for the reply foxhole.

    The part of the room the smell comes from is about 4 metres from the external wall. No damp problems or smells at all on the external wall itself. The roof isn't leaking and there's no measurable damp anywhere above skirting board level so it doesn't seem to be getting in from above either. The neighbours have had damp problems but they've been resolved and weren't in our party wall - that was due to old plumbing on the other side of their house.

    I didn't get the structural engineer out specifically to look at this - he was looking at some cracking we've had in the bay. Just thought it was worth getting his view on the smell while he was here as I've drawn a blank elsewhere. I've had a long chat with a chartered building surveyor too, who didn't have any ideas. Haven't managed to persuade any surveyor to actually come out without paying for a full house survey, and the one I didn't speak to was skeptical that he'd find the source in person anyway.

    Who do you think I should be asking?
     
  5. foxhole

    foxhole

    Joined:
    14 Mar 2006
    Messages:
    16,230
    Thanks Received:
    1,817
    Location:
    Kent
    Country:
    United Kingdom
    Do you have a chimney ? How many pots on it , how many hearths?
    A plan showing layout maybe helpful.
     
  6. Deerhound

    Deerhound

    Joined:
    1 Mar 2016
    Messages:
    17
    Thanks Received:
    0
    Country:
    United Kingdom
    There's no chimney on the smelly side of the room. There's a blocked off fireplace on the other side of the room, 5m away. That chimney is open at ground floor level.

    Have a look at the floorplan of this house. It isn't my house but it's very similar - at least on the first floor.
    https://www.zoopla.co.uk/for-sale/details/55433039

    The smell is strongest in right the top left corner of "Bedroom 1", at around floor level. It's also quite noticeable on the back side of that wall in the hallway at the top of the stairs. We've got a fitted cupboard just on the other side of that wall but it doesn't have a back on it - i.e. there's no cavity between cupboard and wall for mould to be growing in, just some ancient wallpaper. You sometimes also get the smell halfway along the same side wall of Bedroom 1, 2m from the front of the house, but it's much weaker there. The smelly spots are also those where the damp meter measures 16%ish in the bricks.
     
  7. Sponsored Links
  8. foxhole

    foxhole

    Joined:
    14 Mar 2006
    Messages:
    16,230
    Thanks Received:
    1,817
    Location:
    Kent
    Country:
    United Kingdom
    Looks like a parapet wall separating properties, they are a regular problem for causing damp if not maintained .
     
  9. Deerhound

    Deerhound

    Joined:
    1 Mar 2016
    Messages:
    17
    Thanks Received:
    0
    Country:
    United Kingdom
    Yes, it's a parapet. It's weird though if it is from the parapet, as the damp doesn't seem to occur above skirting board level on the first floor. Can't find any damp in the party wall at loft level. I'll check again when we next get a decent bit of rain.
     
  10. Deerhound

    Deerhound

    Joined:
    1 Mar 2016
    Messages:
    17
    Thanks Received:
    0
    Country:
    United Kingdom
    https://photos.app.goo.gl/GoK9u3MZssyiBN7L9

    Here's the parapet from both sides. The rendered side is my neighbours. The rooves are south facing and the neighbours' west-facing side of the parapet takes most of the weather. The dark vertical lines might suggest some kind of problem in the past? It does look like there might also be a small gap in the coping tiles at the peak. Can't see any problems on my side.

    I've also been up in the loft again with my damp meter just now. I can't get a reading off the bricks but the lime mortar does read around 16% damp (or salty) at the peak, underneath the gap in the coping tiles. But that falls to 8-10% halfway down the wall and maybe 3% near loft floor level. So I'm struggling to see that as the clear source of the problems at skirting board level on the floor below.

    What do you think?
     
  11. foxhole

    foxhole

    Joined:
    14 Mar 2006
    Messages:
    16,230
    Thanks Received:
    1,817
    Location:
    Kent
    Country:
    United Kingdom
    Damp meter does not record damp in brickwork, a core sample is required and equipment you won't have.
    I would be wondering why the render has been applied, tends to cause problems rather than resolve any, the damp cannot leave the wall and is trapped, falls thru the brickwork following the easiest course. It can emerge anywhere on the party wall at either side. Streaking would indicate loss of mortar on the cap tiles encouraging rain to fall from each joint.
     
Loading...

Share This Page