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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: Bathroom ceiling mould problem, concrete soffit

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    • CommentAuthorShevek
    • CommentTimeNov 14th 2021 edited
     
    - Existing block of apartments (concrete frame, northern Portugal)
    - Bathroom is internal with no windows, ceiling is concrete slab with plaster finish
    - Building is badly insulated with draughty windows (apart from ours, which now has new windows)
    - Crappy little intermittent fan at high level in the wall (which is probably the main culprit)
    - There appears to be have been a mild but longstanding issue with (presumably) black mould

    I sprayed the ceiling with bleach when we moved in, which improved how it looked on the surface but also made some of the paint peel off and I've since scrapped it and there are still little spots of black in the plaster behind the paint.

    What's the long term solution?

    1. Remove all plaster, re-plaster and change fan unit to continuous extract?
    2. As above but add suspended ceiling with very carefully installed VCL?
    3. As item 2 but add larger d-MEV fan unit or even MVHR

    If we added a suspended ceiling, would spraying the concrete soffit with polyurethane foam (after removing plaster) help guard against mould or just provide it a hiding place and make it worse?
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    • CommentAuthortony
    • CommentTimeNov 14th 2021
     
    Clean the fan grille and make sure that it is extracting ideally fit a new Svara fan, these think for you and are programmable via an App.

    Anti mould paint would help

    Replastering won’t help , ventilation will, some heat might be needed too
  3.  
    I would expect spraying the ceiling with polyurethane foam, if a good thickness was applied, would solve the problem. Any insulation applied should be bonded to the ceiling otherwise air and therefore mould will get behind it.
    The real fix would be external insulation to the affected parts - but I guess this is not an option.
  4.  
    Is there any external wall or is the room all internal? ISTR you are not on the top floor?

    If it's internal, then insulation might not help much, unless there's some good reason why the ceiling should be thermally connected to the outside? Have you tried taking surface temperature measurements with an IR to see if the ceiling is much cooler than other surfaces in the room?

    Ventilation is the answer, and a better fan can be trialed cheaply while you are thinking about more drastic options. If there is any external wall then think about a single room MHRV (the kind with a spout that sticks out of the wall and includes extract and intake) - they are cheap and easy to install, though less quiet and effective than a full MHRV.
    • CommentAuthorShevek
    • CommentTimeNov 15th 2021
     
    Thanks guys. That fan looks like just the ticket, thanks Tony. Great idea to add some heating too; a heated towel rail would probably help a lot.

    Above us is another flat, so no chance of external insulation. It's just relatively cold because the whole building is badly insulated and draughty but I haven't actually measured it. Maybe it's not so cold.
    • CommentAuthorLF
    • CommentTimeNov 15th 2021
     
    A bluetooth temperature and humidity logger are about £10 or so for a pair. You can see trends on your phone and help optmise how long you need fan on for.
    • CommentAuthorShevek
    • CommentTimeJan 11th 2022 edited
     
    Just installed the Vent-Axia Svara and really happy so far (thanks Tony).

    Installation and commissioning was very easy. My only criticism is that the aperture I was retrofitting it to was 130 mm (and it should be 110 mm). This would have been fine except that there's a switch on the back side which interrupts some of the rubber seal, so I didn't get an ideal seal of rubber against tile (I offset it toward the switch to get at least 1 ring of seal all the way around).

    It's very quiet on trickle, but we'll see if I can hear it during the night. I see we can adjust flow between 0-100% for each preset which is nice.

    My only question is, why would they set the default fully boosted setting to 88%? Why not 100%?

    (as an aside, the floor structure here is crazy. It's beam and block but the blocks are some kind of hollow core bitumen-based block. No wonder we can hear everything the neighbours do)
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    • CommentAuthorShevek
    • CommentTimeJan 11th 2022 edited
     
    deleted
    •  
      CommentAuthordjh
    • CommentTimeJan 11th 2022
     
    Posted By: ShevekMy only question is, why would they set the default fully boosted setting to 88%? Why not 100%?
    Are you sure the 88% is a flowrate? I would have thought that setting was the humidity (RH) level at which the boost activated, no? So I'd be tempted to make it lower rather than higher.
    • CommentAuthorShevek
    • CommentTimeJan 11th 2022
     
    Yeah, it's the flow rate. Turns out you can switch the units to litres per second. So 88% is 25 litres and 100% is 30 litres.
    •  
      CommentAuthordjh
    • CommentTimeJan 11th 2022
     
    Ah, OK. I guess that's like our nominally 300 m³/hr maximum MVHR unit then. The default maximum rate setting is 225 m³/hr. I've never had cause to need more so I've never queried why. I just assume it's to do with product longevity and also noise levels.

    So what RH does the boost trigger at then?
    • CommentAuthorShevek
    • CommentTimeJan 12th 2022 edited
     
    It doesn't say and I can't find a figure online either.

    We left the bathroom door open last night and couldn't hear it.
    •  
      CommentAuthordjh
    • CommentTimeJan 13th 2022
     
    Actually just rereading the last few posts again, I still don't understand. 25 l/s is 90 m³/hr which is an awful lot of air and would make quite a noise in such a small duct, I think. It's also a lot more than normal for a bathroom or even a kitchen extract. Can you force it onto boost rate to check what it sounds like?
    • CommentAuthorShevek
    • CommentTimeMar 20th 2022
     
    Posted By: djhActually just rereading the last few posts again, I still don't understand. 25 l/s is 90 m³/hr which is an awful lot of air and would make quite a noise in such a small duct, I think. It's also a lot more than normal for a bathroom or even a kitchen extract. Can you force it onto boost rate to check what it sounds like?

    Yeah, I can boost it via the mobile app.

    At 30 l/s (triggered by humidity or boost switch) I can hear it outside the bathroom door with the door closed
    At 19 l/s (triggered by light sensor) I can just hear it outside the bathroom door with the door closed
    At 10 l/s (trickle mode) I can't hear it outside the bathroom door with the door closed and in the bathroom it's a very light hum

    The app is really great. The modes and sensors are very configurable. And most importantly the bathroom is always nice and dry now, and we're never annoyed by noise.

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