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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorluz13827
    • CommentTimeAug 31st 2021 edited
     
    Hello, I got a few helpful comments about rising damp as part of another post, so I just wanted to post a bit more detail here, incase someone has some valuable insight.

    Victorian terrace/ground floor flat. Purchased/moved at the end of 2020. The wall with the Openreach box is solid brick external wall. The wall with the electrical socket is an internal brick partition wall (separates our flat from the communal hallway).

    The sofa was backed into this corner before we noticed mould around February, so I am sure the lack of airflow has not helped. However the damp looking patch on the internal partition wall seems odd. It wasn't wet to the touch. These photos were taken in March, and the damp patch has faded a little since then.

    A surveyor believes it's rising damp with water coming through the gaps at the front of the property and via capillary action through the internal partition wall. Does this seem possible? He said the readings weren't too high (but I'm unsure what they were). Will be taking apart the flooring soon so will be able to take a better look - is there anything specific we should be checking for there?

    When we renovate, we'll be ensuring we use hygroscopic materials and solving for any condensation issues.

    Thanks for any insight!
      e and f - INSIDE - corner of external wall and INT-2.png
    • CommentAuthorluz13827
    • CommentTimeAug 31st 2021 edited
     
    Photo of outside. The surveyor believed water ground be getting through small gaps where the wall meets the external ground. Or also through cracks in the paving a bit further away (not visible in photo)
    • CommentAuthorluz13827
    • CommentTimeAug 31st 2021 edited
     
    We also have some mould below the bay window. I think immediately below the bay window is likely due to the windows needing replacing. however, there's mould at the bottom too, which I'm unsure about.
      d - INSIDE - mould on external wall, below window sill.png
    • CommentAuthortony
    • CommentTimeSep 1st 2021
     
    Most likely condensation, sorry

    See https://readinguk.org/draughtbusters/

    Colder bits of the room tend to de problem areas,furniture can reduce air circulation and prevent heat getting there, condensation moves there with no air movement

    Looks like a cold draught behind bottom of skirting to me too
    • CommentAuthorluz13827
    • CommentTimeSep 1st 2021
     
    @tony thank you! If it's condensation, that's much better news, because it's more easily resolvable. I was worried it could be something structural that we're unaware of. Behind the internal partition wall, where the communal hallway is, there's no heating - do you think we need some heating in that communal hallway to help protect our side of the wall from getting too cold? Or do you think if we avoid having furniture against that wall, it should be fine.
  1.  
    Is the internal floor level higher than the external one (the air vent under the bay window suggests it is, if that vent is ventilating an underfloor space).

    I'd agree that it's most likely condensation.

    Taking a bit of plaster off the affected area might give you some clues - whether the dampness seems to be originating on the surface of the plaster, or moving through from the brickwork.
    • CommentAuthorEd Davies
    • CommentTimeSep 1st 2021
     
    How about taking off a bit of that beading to see if there's any mould on the back? My guess would be that it's, as tony and lineweight suggest, condensation and that the back of the beading will have much less, if any, mould.
    • CommentAuthorluz13827
    • CommentTimeSep 1st 2021
     
    Really useful, thanks @lineweight and @ed - the internal floor is higher than the external ground levels. The vents are for ventilating the underfloor space. Good idea to remove some of the plaster and beading and inspect the wall behind, as that should indicate whether condensation or not. I'll try that, thank you!
    • CommentAuthortony
    • CommentTimeSep 1st 2021
     
    I can tell you if your wall is damp if you drill a hole 65mm deep, collect the dust and send it to me in a double wrapped zip bag - almost certain moisture will below 4% most likely about 2%
  2.  
    Also that photo of the inside under the bay window... the mould is under the sill and near floor level with apparently dry portion inbetween, which would match condensation gathering in cold/poorly ventilated spots, rather than damp moving upwards from below.
    • CommentAuthorvord
    • CommentTimeSep 1st 2021
     
    The way these buildings used to operate was clever. The lime mortar on the outside allowed the whole wall to dry out and the breathable coverings inside meant that the internal walls remained dry and mould free whatever you did.

    Now the exterior has been painted in waterproof paint the wall will be sodden wet. Interior walls will be in plastic emulsion. The cold will suck moisture from the air inside onto the walls.

    My house was green/black with mould inside when I bought it. Removing the masonry paint from the exterior and lime pointing everything was the most useful thing I did. But it was a bit of a faff.
    • CommentAuthorluz13827
    • CommentTimeSep 1st 2021 edited
     
    @vord Is the masonry paint a big deal? It was done by our upstairs neighbours before we bought the flat- they are the other freeholders (so I don't think they'd be too thrilled with us suggesting to remove!) I assumed that it would still allow water vapour from inside to leave (if of course the insides are made from breathable materials, which we will be doing). Do you think the paint could be trapping moisture in the wall?

    I also had another question regarding furniture backing onto walls. In our new extension, we will have a row of kitchen units (on the floor) against an internal wall. We are a bit limited with space, so this is unavoidable. Is there anything we can do to minimise potential condensation issues behind the kitchen units? We plan to use clayboards and clay finishes to help buffer humidity, so I'm thinking that should help. Along with correct ventilation etc. Then it would be OK to have things backing onto the walls?
    • CommentAuthortony
    • CommentTimeSep 1st 2021
     
    Internal walls tend not to gather condensation
    •  
      CommentAuthordjh
    • CommentTimeSep 1st 2021
     
    Posted By: luz13827@vord Is the masonry paint a big deal?

    Depends what paint was used. Some is breathable (i.e. vapour permeable), some isn't.

    I also had another question regarding furniture backing onto walls. In our new extension, we will have a row of kitchen units (on the floor) against an internal wall. We are a bit limited with space, so this is unavoidable. Is there anything we can do to minimise potential condensation issues behind the kitchen units? We plan to use clayboards and clay finishes to help buffer humidity, so I'm thinking that should help. Along with correct ventilation etc. Then it would be OK to have things backing onto the walls?

    Kitchen units tend to have a void behind them, to run wiring and/or plumbing. Floor-standing units typically also stand on legs and thus have a void under them as well, which is usually closed with a plinth/footboard material. If the plinth is continuous and there is a worktop sealed to the wall on top then there won't be much air movement to carry moisture to the wall behind the units. Equally it would be possible to vent the space if you wanted by inserting vents top and bottom. Clayboards and clay paint will help minimise any issues. And as Tony says internal walls don't cause as many problems since they tend to be at the internal temperature. So I think you're unlikely to have a problem.
    • CommentAuthortony
    • CommentTimeSep 2nd 2021
     
    Re painted bricks, not great, lime pointing will solve it or limewash after removing paint. It just might be ok , suggest sampling for entrapped moisture
    •  
      CommentAuthordjh
    • CommentTimeSep 2nd 2021
     
    Note that limewash is a high maintenance coating. It is applied in several thin coats and more coats need to be applied at intervals, as the surface wears away. Other paints, such as silicates, offer most of the same advantages and are harder wearing. But limewash is cheap.
    • CommentAuthorluz13827
    • CommentTimeSep 2nd 2021
     
    Apologies, I meant that the kitchen units will be on an *external* wall.. But the units will be sealed to the wall. Regarding the plinth, we were debating whether to have a continuous one, or to build in some extra drawer space into the plinth area. However, it sounds like continuous may be better, to avoid moisture getting in.

    Thanks re: paint advice. I will see if the builders can get a sample to check for moisture levels.
    • CommentAuthortony
    • CommentTimeSep 2nd 2021
     
    There can be problems with all cupboards on external walls, best to have backs on them

    You cant stop damp/condensation getting to places by sealing them so plinth drawers will be OK , moisture is transported through air rather than by air, subtle but it means that it can travel through all permeable materials, through tiny gaps between connected places, pores, fabrics, walls etc
    • CommentAuthorphiledge
    • CommentTimeSep 2nd 2021 edited
     
    Posted By: luz13827Apologies, I meant that the kitchen units will be on an *external* wall..

    If the kitchen is in the new extension, the walls will have high levels of insulation and thus be relatively warm. We dont have any problems with condensation behind our kitchen units in a build from 20 years ago.
    • CommentAuthorluz13827
    • CommentTimeSep 2nd 2021
     
    @tony "best to have backs on them" do you mean have backs on the cupboards? That will be the plan, I believe, with a small service gap behind.

    Hopefully all the other ventilation + humidity buffering materials help as we don't have an alternative place for the kitchen units to go! Am I right in thinking if relative humidity is maintained at correct levels, condensation is largely not an issue? It's only if RH rises? If so, I'm confident we'll be ok.
    •  
      CommentAuthordjh
    • CommentTimeSep 2nd 2021
     
    Posted By: luz13827Am I right in thinking if relative humidity is maintained at correct levels, condensation is largely not an issue? It's only if RH rises?

    Yes, as long as the wall is properly insulated and RH is reasonable (<60%) there shouldn't be any problems. Corners are at most risk, where two walls join and where a wall meets the floor. Hence the emphasis on thermal bridge-free design.
    • CommentAuthorvord
    • CommentTimeSep 2nd 2021 edited
     
    Posted By: luz13827@vord Is the masonry paint a big deal? It was done by our upstairs neighbours before we bought the flat- they are the other freeholders (so I don't think they'd be too thrilled with us suggesting to remove!) I assumed that it would still allow water vapour from inside to leave (if of course the insides are made from breathable materials, which we will be doing). Do you think the paint could be trapping moisture in the wall?


    I had a bad experience with masonry paint. Many masonry paints (apart from silicate and of course lime) claim to 'breathable' but aren't to any real degree. On brickwork you'll get cracks and unpainted bits which let water in but the water can't get out again. That makes the wall wet which attracts condensation and mould on the outside so they paint it again after 5 years. Mine ended up like the photo. There were damp patches inside on the first floor with no other issues other than the paint.

    https://www.the-salutation.co.uk/blog/wp-content/uploads/2015/04/1-failing-paint-624x468.jpg

    I had the paint stripped off with a DOFF steam pressure washer system with paint stripper. It had been so wet for so long under there that the lime mortar had melted away so I needed to re-point. It was an expensive year.

    https://www.the-salutation.co.uk/blog/wp-content/uploads/2015/04/stripping-north-wall-624x466.jpg

    That worked. There were many other causes of damp such as ground levels higher outside than inside, leaky gutters etc. I've been trying to make things breathable on the outside and inside. Inside I can't in many rooms due to modern materials but the outside is good. The last remaining damp I think is caused by a leaking water pipe underground. That's the next job.

    Sorry, images didn't work. They are from here: https://www.the-salutation.co.uk/blog/paint-stripping/
    • CommentAuthortony
    • CommentTimeSep 2nd 2021
     
    There are no guarantees with condensation, as air cools RH rises, cool surfaces gather condensation. My rule of thumb for homes is not to have surfaces below 12C in winter, below that and it is near impossible not to have condensation problems.
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