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  1. #1
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    Default Condensation in metal shed

    The last few days, and last Saturday week, had a lot of water dripping from the roof in my shed. (actually it is a 130m2 industrial strata unit, so a little bigger than most of your sheds, but I'm wondering if any of you have encountered a similar problem?)


    If I get there at 7 or 8AM, and there might be some water trickling down the external gutters, but no rain for days, so this is morning dew. Dripping inside occurs 9 or 10AM, usually when the sun is out. Air is humid –Hydrometer says 70% or 80%.


    Concrete floors and walls, ceiling is 6 or 7m high, metal foil backed insulation, and some translucent strips for light. Water is only dripping off the underneath of the translucent strips.


    Climbed up on a ladder today to investigate. Couldn't see any drips, but could feel some wet patches, and then finally saw condensation above the insulation:
    IMG_1717.jpg




    So, I can live with it, but dripping on timber or paperwork or computers is annoying.

    Can't afford air conditioning, but wondering if an exhaust fan might help on humid mornings?

  2. #2
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    Hi Nigel, I'm not sure what the ambient temperature is in your shed, but if it is warm enough an air conditioner or dehumidifier would almost certainly dry the air and cut condensation. I can't recall unfortunately what my local refrigeration guy told me about what a suitable temperature was, but some years ago now a carpeted building that my Lions Club had built was flooded and I was asking about using an air conditioner to help dry it out. With the then expected daily temperatures in N.W. Tasmania, he felt that using an air conditioner was not likely to be successful.
    On the other hand, over the last couple of days I have extracted 5.5 litres of water from a 40 foot container, and its contents after noticing condensation all over a machine lathe stored there, and lots more about to drip from the roof. The container is un-insulated and I ran a 1000 watt QH floodlight, aimed at the base of the lathe for one day and then shifted down the container to other machinery for the second day. For the whole time a Delonghi de-humidifier was running, and I measured 2.5 litres the first day and 3 litres this morning. I have since turned the 1kw heater off, and left the dehumidifier on, but the signs of condensation had almost gone after the first day, just a very few drips of water on the ceiling, and this morning no signs of water at all, although I am under no illusion that the space is entirely dry. It will be interesting to see how much water I have collected tomorrow morning.
    I will say that on day one we had a frost and the temperature was possibly around -2ºC, and since then it has been warmer, but more humid and overcast, with almost zero wind. Surprisingly the completely uninsulated 40 foot Hi Cube container felt distinctly warmer inside than outside, but unfortunately I can't say what the temperature was, but even with the heat losses one would expect, the 1kw QH floodlight was making a noticeable impact on the temperature inside the container.
    I doubt that an exhaust fan will help much unless you are producing water vapour in the shed. Cooking or clothes drying for example will produce lots of water vapour, (as will any unvented flame heater) and if not vented outside, will collect and condense on cold surfaces. If your shed is relatively air tight, then you may be able to dry the air within, and stop condensation forming. If humid air from outside has ready access, then you will be fighting a loosing battle. On the other hand if you get a warm sunny day with very little humidity and a gentle breeze, opening up your shed would allow the warmer and drier air to dry out your walls, ceiling, ceiling insulation and any other damp areas.
    If the translucent strips in the roof are Laserlight or similar then in cold weather you are likely to have condensation forming there, because they chill down more than other areas, and water vapour will tend to condense there. I believe that the roof light material which is like core flute on steroids is less likely to have condensation forming on it because it insulates against heat transfer better than thin walled transparent plastic sheeting.
    It may be worth trying either a dehumidifier of a window mount air conditioner just mounted on a bench or trolley, (with both air circuits blowing into your shed) and see if it makes any difference or not. With any luck you may find something at a tip shop, (that's where I got my de-humidifier) or gumtree/ebay for not much, and you may not have to use it that much once you get it all dried out.
    Just remember to collect the condensate in a bucket.

  3. #3
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    Thanks for the compliment with the "likes" folks, and as a follow up report, I have just emptied 2.75 litres more water from the de-humidifier, some 28±hours since the last check. The heater has been off the whole time, and we are now virtually in the cloud base with light rain falling. The rain has not been falling continuously since yesterday, but it has been raining on and off during that time period.

  4. #4
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    Quote Originally Posted by nigelpearson View Post
    Water is only dripping off the underneath of the translucent strips.
    I have a similar situation in one of my sheds - it all has aircell insulation under the tin, except where there's a section of clear polycarbonate. I get condensation on the tophat battens, but only on the 800mm or so under the polycarbonate - the rest of the batten is dry.

    I assume this is because the un-insulated polycarbonate allows heat loss that cools the section of batten underneath it enough to form condensation.

    My first thought has been to use contact adhesive to glue insulation to the surfaces of the battens, but it occurred to me that the cold polycarbonate could also be condensing water, and that's not so simple to insulate...

  5. #5
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    Assuming the shed is left open:..ie door width allows good ventilation.

    If the concrete slab gets wet from external sources only remedy is heating/dehumidification or other protection ie constant oiling waxing etc.

  6. #6
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    I’ve had similar probs from the polycarbonate panels on my roof.
    We replaced the rusty corro with new painted stuff and put ‘glass/foil under it.
    Of course the drips off the clear were on the table saw amongst other spots.
    I have a 40 x 60 ft shed about 200 metres from the bays and it’s not very well sealed around the windows louvred etc.
    Leave any tools out and they are rusty in a week or less.
    H.
    Jimcracks for the rich and/or wealthy. (aka GKB '88)

  7. #7
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    Quote Originally Posted by Ropetangler View Post
    Hi Nigel, I'm not sure what the ambient temperature is in your shed
    Outside temp (of my car) got down to 2°C on that morning, but I don't have data loggers for temp or humidity in the factory unit. I think it was 6°C when I got there at 7AM.




    I doubt that an exhaust fan will help much unless you are producing water vapour in the shed.
    Valid point. If humidity outside is also 70%, pulling air in will do nothing.

    Apart from sink/toilet/hot water heater overflow, and a little coolant in the bandsaw and lathe, factory is dry.

  8. #8
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    Quote Originally Posted by RustyArc View Post
    I have a similar situation in one of my sheds....

    My first thought has been to use contact adhesive to glue insulation to the surfaces of the battens, but it occurred to me that the cold polycarbonate could also be condensing water, and that's not so simple to insulate...

    That was my thought also, the uninsulated fibreglass/polycarb is condensing and needs insulation.

    Extra layers of anything would help - think double insulated windows - but it is a pain to install up there.

    First hacky idea was sheets of clear acrylic attached underneath.
    Partly to insulate, partly to collect the drips and channel them somewhere.

  9. #9
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    Quote Originally Posted by eskimo View Post
    Assuming the shed is left open:..ie door width allows good ventilation.

    If the concrete slab gets wet from external sources only remedy is heating/dehumidification or other protection ie constant oiling waxing etc.

    Usually closed up. Two roller doors - 4.3m wide and 5.3m high:
    Unit 26.jpg


    When I am there I usually only half open one door - it keeps the wind and dust out - and close up at the end of each day (6 or 7PM). Floor slab is epoxied (so hard to estimate dampness). Walls are painted with something acrylic, and seem dry.

    That said, though;

    1. When it rains heavily, a little water pools on the floor between the two roller doors.
      I should grind some extra fall on the concrete threshold.
    2. There are a lot of spider webs in there. I assume they are getting in under the roof/gutter/insulation, but thinking about it, there is one corner with a gap in the mastic sealer between the wall slabs.

  10. #10
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    Reading your post gives me the impression it is created not just by the ambient temps outside but by temps inside also. After a day using machines which get warm to hot as well as human activity it warms up inside. This warm air of course rises and as it cools condensation forms. More so if heaters are used internal. We found this a problem during winter in the factory when apprentice. Latter on when driving buses & coaches and th ery have roof and ceiling with insulation between. Fitting of whirlybird extractors reduces it some what but not totally.
    As the sun warms the roof of course the cold underside of surface will form condensation the air bel oow being colder warms up causing steam just like any surface sitting in the sun. If you can use a oil or wood heater to warm the internal air faster it may limit it.

    Sent from my SM-T580 using Tapatalk

  11. #11
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    Quote Originally Posted by wheelinround View Post
    created not just by the ambient temps outside but by temps inside also. After a day using machines which get warm to hot as well as human activity it warms up inside. This warm air of course rises and as it cools condensation forms

    Perhaps, but I think most of the time the dripping seems to be due to external humidity? e.g. humid days.

    (went looking for historical humidity data for Revesby. no luck)

    Last weekend/week, dripping was Saturday, Monday and Tuesday. Workshop was unused on Sunday.



    Still thinking about heating or fan ventilation. I have a large wall mounted fan, but no ceiling exhaust fans. Don't really want to leave anything running each night if not needed, but am too lazy to check forthcoming weather when leaving, so would prefer to have sensors to trigger something.

    (plus, having an "open" ceiling ventilator in a cold workshop in winter seems a little wasteful?)

  12. #12
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by wheelinround View Post
    Reading your post gives me the impression it is created not just by the ambient temps outside but by temps inside also. After a day using machines which get warm to hot as well as human activity it warms up inside. This warm air of course rises and as it cools condensation forms. More so if heaters are used internal. We found this a problem during winter in the factory when apprentice. Latter on when driving buses & coaches and th ery have roof and ceiling with insulation between. Fitting of whirlybird extractors reduces it some what but not totally.
    As the sun warms the roof of course the cold underside of surface will form condensation the air bel oow being colder warms up causing steam just like any surface sitting in the sun. If you can use a oil or wood heater to warm the internal air faster it may limit it.
    There has to be moisture in the air inside the shed for condensation to form on a cold surfce. If there's no moisture then is cannot happen irrespective of the temperatures involved. Typically what happens is that the inside of a shed shed gets warmer during the day. Most people don't realize that using any machines ultimately generates heat - all those mechanical Watts get converted into heat. Because warmer air holds a lot more moisture than cold air, the humidity inside a shed naturally builds from things like
    - worker breath, which contains loads of water inside a shed
    - anything that involves flames or stick welding - combustion produces lots of CO2 and water
    - running motor vehicles or any combustion engine
    - and anything damp like wood or even dust that always holds some water partially drying out releasing water back into the air.
    Then at night when every thing cools down the air cannot hold as much water so it condenses out on any cold surface like the underside of a cold roof.or cold machine surface and is often what causes rust

    Like wood dust the best thing to do is capture and vent humid air at source (while its generated). Next best is general forced ventilation (whirly birds largely ineffective on a big shed)
    The bigger teh shed the more force is required.
    Below is what I mean by forced.
    That's a 3HP barn fan used by the Dunsborough mens shed.
    Its a bit noise but it sure works.
    IBigAssFan2.jpg

  13. #13
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    Quote Originally Posted by nigelpearson View Post
    Perhaps, but I think most of the time the dripping seems to be due to external humidity? e.g. humid days.

    (went looking for historical humidity data for Revesby. no luck)

    Last weekend/week, dripping was Saturday, Monday and Tuesday. Workshop was unused on Sunday.



    Still thinking about heating or fan ventilation. I have a large wall mounted fan, but no ceiling exhaust fans. Don't really want to leave anything running each night if not needed, but am too lazy to check forthcoming weather when leaving, so would prefer to have sensors to trigger something.

    (plus, having an "open" ceiling ventilator in a cold workshop in winter seems a little wasteful?)
    Revesby NSW bloody freeze in winter fry in summer. Worked at Stillwells trucks.
    The ground surface is regarded as moist low lying constantly flood prone.
    The closer to Georges River the colder it gets.
    The industrial area is generally low lying and with Bankstown airport giving a large open space brrrrr.

    Sent from my SM-T580 using Tapatalk

  14. #14
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    would a industrial gas heater help?https://www.totaltools.com.au/132881...0aAiONEALw_wcB

  15. #15
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by mick21 View Post
    If gas is going to be burned inside a building and exhaust is not flued or vented it's going to add massive amounts of water to the shed (not to mention loads of CO2).

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