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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorlouis14
    • CommentTimeDec 9th 2018
    Hello folks. I was on this forum a bit several years ago whilst I had dreams of self-building an eco-friendly house - dreams which have been dashed for one reason or another, sadly. However, I remember this place as filled with very technically savvy people, and I wanted to ask some advice about damp and black mould.

    I lived for 12 years in a smallish, ground floor, two bedroom flat - ex local authority, 1930s built mansion block. I rented it out last summer. The tenants are having trouble with condensation on the windows and black mould growing in various places in the flat. It's a total surprise to me, as the only place I saw even a little bit of mould in all the time I lived there, was in one corner at the back of the airing cupboard. But they are getting it in several rooms - kitchen, bathroom, loo and also one of the bedrooms.

    I had a specialist damp proofing company visit the flat to advise what could be done. They said I should have installed a 'condensation control system' which they explained is a unit that draws in air from the outside, warming it and providing a little positive air pressure to push the air from inside the flat out through the wall air vents.

    I had it installed about five weeks ago and it doesn't seem to be helping at all. They've been in to 'turn it up to full' but I'm not sure it's improved things. So I'm at a bit of a loss as to what I can do now. The tenants say they open the kitchen window whilst cooking, and keep the saucepan lids on. There's a washer/tumble dryer in the flat, which is the condensing dryer type. There are small extractor fans linked to the light switches in both the kitchen and the bathroom. The uPVC double glazed windows have little vents in them, and there are wall air vents in the loo and bedrooms. Like I say, I never had a hint of a problem whilst I lived there, either by myself or with my partner for a few years.

    They are a couple with a baby, so I'm anxious to find a solution; I don't want the flat to be a health hazard for the littl'un.

    I'd really appreciate your thoughts and advice.

    Thanks, L14.
    • CommentTimeDec 9th 2018
    Whatever they're doing they may still not be ventilating enough.

    I don't like the idea of pushing their warm out through the vents and chucking it away. A couple of single-room MHRV fans in keys rooms might be a lot better at dumping the moisture while retaining the heat, eg in our kitchen:



    • CommentAuthorphiledge
    • CommentTimeDec 9th 2018
    The interior humidity is to high for the surface temp of the walls/windows, so the moisture is condensing. Stating the obvious, the humidity needs to be reduced or the surface temp increased.

    For the humidity, you need to look at all the sources of moisture and reduce them if you can, followed by upping the ventilation. Masses of moisture comes from breathing, plants, clothes drying, showering. Opening a single window while cooking wont let out much moisture unless theres another opening to create a flow of air through the flat and take the moisture outside.

    The cold surfaces can only be dealt with by adding insulation or turning up the flats heating.

    Im guessing that with a baby the family are possibly staying in much more than you did and probably doing more washing and drying? If thats the case it may explain why thing are different to when you were there??
    • CommentAuthortony
    • CommentTimeDec 9th 2018
    UKCMB is worth looking at and my DraughtBusrers website Reading UK dot .org http://readinguk.org/draughtbusters/why-draughts/controlling-condensation/

    PIV is very expensive to run as it constantly throws warmed air away but the tenant pays.

    I like your aims and objectives - as I see it some changes to the way they live are very likely needed.
    • CommentAuthorlouis14
    • CommentTimeDec 9th 2018
    Hi folks

    Appreciate all your replies, thank you. The Tempra P looks hopeful. I imagine I would need one in both kitchen and bathroom. Would you agree? (I don't think noise will be an issue as neither room is near any bedrooms).

    Both rooms already have a similar looking circular vent (as in Damon's article) to the outside that the existing fans are mounted to. Is the unit installation something any competent electrician/builder could do?

    Given that model was bought in 2014, is it still available - or is there a more modern equivalent I should look for?

    • CommentAuthorphiledge
    • CommentTimeDec 9th 2018
    If youve already got extract fans in some of the rooms and still have a condensation problem, then id be suprised if the Tempra P units will make much difference. They will do an air exchange as well as recover some heat but your existing extractors are/could already be doing the air exchange. When new theyll recover some heat but the heat exchangers will need cleaning from time to time and if neglected the heat recovery is likely to drop off putting you back where you are now with extract only.

    Personally Id be looking at why the flat was dryish when you were there and damp now. There maybe lifestyle changes you can ask them to make, before throwing cash at the problem.
    • CommentTimeDec 9th 2018
    Posted By: louis14I lived for 12 years in a smallish, ground floor, two bedroom flat - ex local authority, 1930s built mansion block. I rented it out last summer. The tenants are having trouble with condensation on the windows and black mould growing in various places in the flat. It's a total surprise to me, as the only place I saw even a little bit of mould in all the time I lived there, was in one corner at the back of the airing cupboard. But they are getting it in several rooms - kitchen, bathroom, loo and also one of the bedrooms.

    As everybody has said, almost certainly they're not ventilating the place as much as you used to do, plus (I surmise from what you stated) there are more of them there, and so injecting more moisture into the atmosphere.

    Exactly what is this 'condensation control unit' and why isn't it working? Who specified it? What are the specifications? What have the suppliers and installers said about its performance?

    What kind of relationship do you have with the tenants?
    • CommentTimeDec 9th 2018
    Do the existing extractors run automatically somehow, so that people can't "forget" to put them in boost and thus clear the smog? The one in our bathroom does, on a humidistat, and I think that that helps.

    • CommentAuthorlouis14
    • CommentTimeDec 9th 2018 edited
    The existing extractor fans run from the light switches, and stay on for a few minutes after the lights are turned off. Probably not long enough, especially in the bathroom, to bring the humidity down properly.

    The unit was specified by kenwoodplc.co.uk on the recommendation of their visiting surveyor. It seems to be their own brand 'positive pressure unit' running continuously on a maximum of 16W. (No operator controls). More than that I can't tell you. I have no specs sheet.

    My contact with the tenants is via a local letting agent, as I do not now live locally. Other than the problem with damp and mould, there's no problems with the tenants.

    I will talk to the letting agent tomorrow about exploring all the ways they can keep things dryer. I've also forwarded Tony's link to the agents.

    • CommentTimeDec 10th 2018
    Posted By: djhWhat have the suppliers and installers said about its performance?

    If the reason you haven't answered this is because you haven't asked, then ask them. If you've asked and they haven't answered, then chase and then start legal proceedings.
    A dehumidifier fitted in the kitchen and plumbed into the waste would reduce the humidity and warm the room a little.
    • CommentAuthordickster
    • CommentTimeDec 10th 2018
    With my property manager hat on:

    Block of four very poorly built 1952 flats. Small damp problems on ground floor, elderly tenants, condensation related. Exit old for new young tenants, absolute nightmare, black mould in every room, every surface, despite prior advice, warnings and step by step instructions from me regarding ventilation, closing kitchen door when cooking, etc.etc.etc.

    Bottom line was that they had heating on when in, off when out so flats went through at least one condensation cycle per day, not able/willing to afford to keep things hot and ventilated.

    Both ground floor new tenants convince each other that the landlord is at fault and move out. Keen to avoid problems again have single heat reclaiming vent axia type fans fitted in kitchen. Problems solved, but suspect both new tenants heeded rather than ignored my words of wisdom.

    Good luck!
    • CommentAuthorlouis14
    • CommentTimeDec 10th 2018

    I haven't asked for any specifications - mainly because if I had, they wouldn't have meant anything to me. I have now done so.

    Are the portable dehumidifier units that I've seen around an good? I'm sure there are different specifications. What brands should I avoid? What would be a suitable air flow rate? Other things to look for?

    The flat is roughly 10 x 7 metres. I've found a plan of the layout I must have drawn years ago - is there a way of uploading a jpg if that's any help?
    Select 'Choose file' below and browse for it on your computer. This forum's software likes quite small files, though.
    • CommentAuthorlouis14
    • CommentTimeDec 10th 2018
    Ah, the file upload button has mysteriously appeared.

      Flat Floorplan_small.jpg
    • CommentAuthorJeff B
    • CommentTimeDec 10th 2018
    Are the tenants drying washing on the radiators or on clothes horses?

    We have recently bought an EBAC dehumidifer for a tenant which is placed on the upstairs landing and which is collecting a fair amount of moisture from the bathroom and bedrooms and presumably from downstairs too as the stairwell is right there. Probably too early yet to tell how effective this is.
    • CommentAuthortony
    • CommentTimeDec 10th 2018 edited
    Dehumidifiers always collect water, that is what they always do in dry or wet houses or outdoor. Or anywhere.
    • CommentAuthorCWatters
    • CommentTimeDec 11th 2018
    Presumably the windows are double glazed. Perhaps find out if they are getting condensation on the inside of the glass - its not foolproof but a reasonable sign that there is insufficient ventilation.

    We have lived in 4 houses since getting married. Had condensation issues in all of them to varying degrees. When we build our current house decided to fit a MVHR system. No issues in this house.
    This post is getting old, but I will add my 2c. Sorry, this ended up a bit long and random.

    First, I would get a digital device to measure the RH (can be obtained for under 100GBP), with the response time under 5-10s. This will help see if whatever they are doing reduces the RH or not. One needs the RH to be under 70% or, even better <50%, to stop the mould. Anything above 90% is a problem. The effect on the RH will be more immediate than on the mould itself. 3 weeks may, or may not, be enough.

    The existing mould should be bleached, this takes time and should be done with care (gloves, face mask with charcoal filter). If it's in cracks/tile joints, one can soak toilet paper/cotton balls with bleach and stick these in the joints. Takes up to 48 hrs to bleach it. Careful with the Cl2 gas, do not let kids in the bathroom while it's being bleached, esp if they have asthma. Bleaching can also be done with KMnO4 or peroxide, if fumes are problematic . This is what I did in a walk-in fridge room where I work. However, KMnO4 and peroxide should be handled with care (eyes), and research should be done in advance to know how to handle these chemicals. Also, KMnO4 may leave stains.

    There could be an invisible reservoir of black mould, this should be identified. I would check under the shower, and the bath tub. Could even be under the floor tiles in the bathroom.

    If the tennants are having health problems due to the mould, I would focus on controlling the humidity and venting of the bathroom (the likely source) and the bedrooms (the place they spend 8 hrs a day), as priority areas.

    The points on drying clothing that others posted are very good. Cloth-drying indoors seems to be a British thing..., I did not see it much in the US. Prob b.c. energy prices in the US are subsidized. so they use a gas- or electric-heated dryers which are vented to the outsode >>> no problem with humidity due to cloth drying. Cloth line protected from the rain (and placed outside) might be another solution. "Outside storage" in your drawing?

    From the energy efficiency standpoint, using a tumbler-type laundry dryer at 2kW for 2 hrs per load of laundry, once a day, is more efficient than chasing and scrubbin the vapour out of a much larger volume of air, using a 400W dehumidifier 24 hrs a day (see below). 2kW x 2 = 4kw-h, whereas 0.4x24 = 9 kw-h.

    Dehumidifiers (DHs): EBACs are good, but are very costly. I currenntly use a small 200 GBP dessicator-type DH in my walk-in fridge. Some numbers: the fridge room is a 3x5x2.5 meters, it's at 6C, and prior to the DH installation the humidity was >90%. Black mould everywhere. With the DH now running 24-7 at about 400W I extract 2.5 liters per day, and dump it directly down the drain. The effect on the RH (went from 92% down to 50%) was within 3-4 hrs of running the unit, so that was reassuring, and I knew I was on the right track. Of course, one can also see the water tank filled/extracted, as a sanity check. Anyway.... the DH keeps the humidity in the room under 40%, and the black mould is now gone. The unit came from amazon:

    "Meaco DD8L Junior Desiccant Dehumidifier 8 L"

    Just got an MVHR, haven't installed it yet though.

    Sorry, 'my 2c' turned out rather long.

    • CommentTimeJan 1st 2019
    There's an interesting article in the latest PH+ mag about curing damp & mould problems in the Thamesmead estate by ventilation. Novel contract structure made the suppliers responsible for the performance and surprise, surprise it all works :bigsmile:

    • CommentAuthorArtiglio
    • CommentTimeJan 2nd 2019 edited
    Looking at your drawing you’ve basically got little chance of solving the problem. Storage heaters are expensive to run and give little control ( compared to central heating) you show no heating in the kitchen or bathroom.
    Tenants are notorious for turning off fans and closing trickle vents, if they are on low incomes or careful with money heaters will get little use.
    I’ve flats that with one family will be no problem at all, another family moves in and within weeks there are problems. I’ve found trickle vents that have been unscrewed the hole taped over and vent replaced. Fans switched off, windows never opened, higher levels of occupation than would be ideal.
    I’d be a little peeved at the professional advice you’ve received and solutions you’ve been sold.

    If you intend keeping the flat long term, then is it feasible to have gas central heating installed and if not then look at fan assisted storage heaters linked to room stats.

    This won’t be popular advice on a green building forum, but the construction of the flat (given its age) and its likely heat demands mean that without substantial insulation improvement you need to keep the place warmer and or change the tenats behaviour.
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