Condensation

My garage is around 18'x8' it has a corrugated roof panels bit like the asbestos type but I don't think it is asbestos, I do get condensate on it in the cold weather but I don't know which is the best solution to this, I am leaning towards a dehumidifier, what size I am not sure, any advice would be welcome,is insulation a better alternative if so what type is best

Mick

 

Mick

 

Suggest insulating all inside surfaces with Celotex foam or similar or you may want to look at spray on foam methods.

Emgee

Mick you will probably find that you need both, definitely insulate the roof, I would suggest using Celotex sheets, a minimum of 50mm thick but ideally 100 mm, brilliant insulation for workshops.If possible add insulation to the walls as well, the objective is to keep the temperature within the workshop as stable as possible, it is the temperature fluctuations which cause saturated air to deposit moisture as condensation on any cold surface when the air cools. In my workshop I have plenty of celotex insulation and during the colder months, October to March, I have a small oil filled radiator set on low running 24/7 which keeps the temp about 10 to 12 degrees. I also run a dehumidifier which comes on between midnight and 6.00 am, everyday and runs while the electric is on economy seven. The humidity reading in the workshop varies between 45 and 55 % relative humidity. Since I insulated and provided constant low background heat I have not had condensation and therefore no rust. I cant stress enough how effective insulation is in preventing condensation.

Dave

Or in the case of cavity wall insulation causing condensation. I had to jump through loads of hoops to get the stuff removed at my parents house.Caused a right mess.

Insulate, insulate and insulate! Then maintain the temperature above dew point. Dehumidifiers help, but at zero Celsius, any water vapour in the air is likely to condense somewhere.

Compressor dehumidifiers don't work too well at low temperatures. The absorption type use more leccy, but that would help the temperature problem.

I'm just enclosing a lathe for the winter. It is in a sectional concrete panel garage with cement/fibre corrugated roofing sheets. It will have 100mm recticel behind, beside, in front and over on a concrete floor (may yet stand it on some insulation). I did get 5 sheets for about 50-60 quid, so looking for a bit more (rather than having a patchwork quilt at one end). Fingers crossed that there might be some at a sale on Saturday, but may need to think of visiting

the monthly sale at Kidderminster, unless I can find another similar auction site.

I bought two non-running meaco dehumidifiers via epay at about£40 quid apiece. Both repaired at zero cost (I was expecting to get one out of the two as worst scenario). One keeps my small insulated workshop (3.4×1.9×2m approx) warmish and dry, by running it an hour each night (uses 370W), so costs about 25p per week. The lathe enclosure may yet be connected to the workshop, so likely no, or little, extra running cost.

Three sheets of 100mm recticel travel easily on my saxo roof.

Hope that helps.

Thanks gents, I think I'll try the celotax route and see where that gets me

Mick

 

I have an up and over garage door which was just a skin of sheet steel to suck all heat out of the garage. I found that I could slide a 10mm sheet of celotax between the ribs and stays and so covered the whole door and tape the joints now the door can still be opened to let in the better half's car but the difference to heat is amazing. I also run a dehumidifier over night as it also gives off some heat as well as reducing the risk of rust.

David

I think it is fibre cement board on your roof. Years ago I had a garage with it and during winter it dripped. Having just insulated a flat roof, you need to leave an air gap between any insulation and the panels other wise you will get rot. The gap should be ventilated so that you have airflow under the panels. This will keep the roof panels colder than the space below. While four inch is required for living spaces, you could get away with less, though the price difference is small. This will cure the roof but the whole building needs to be done including the floor.

Hi there, Mick,

NDIY, above, has said 'Compressor dehumidifiers don't work too well at low temperatures' - I'd put it stronger than that. Unless you can get the temperature up you won't get your money's worth from a dehumidifier.

You need to check that your space isn't too well ventilated or your dehumidifier will be trying to dehumidify the UK!!!

I've personally found that the Myford plastic cover has done a good job of keeping my ML7 rust-free - other folks have reported that they make things worse!?!?

If you're shopping for Kingspan or Cellotex, have a look at 'Seconds and Co Ltd.', they might be cheaper than your local Builders' Merchant despite their having to ship to your door. I bought 3½ sheets of 3" from them and was pleased with what I got.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 30/10/2017 17:20:24 (to correct thickness)

Edited By Swarf, Mostly! on 30/10/2017 17:21:31

I keep my main emphasis on product - I do Model Engineering to amuse and amaze friends and family. For that reason I'm unwilling to engage with time-consuming infrastructure or tooling projects unless they're absolutely necessary.

So I just use a dehumidifier. In a previous house I was lucky and could easily pipe the condensate away, but where I am now I have to empty the 2L tank every couple of days.

If I forget, and find the lathe with condensation on it, a wipe with a flannelette rag removes it. Very occasionally a thin layer of rust appears, but a bit of scotchbrite and WD40 will take that away as if it had never been. But with the machinery in use nearly every day, that doesn't often happen.

It's your lucky day - St Albans MES website has an article on this.

A useful by product of the dehumidifier is 'distilled' water fro your boilers.

The absorption type dehumidifiers that give out heat may work better when cold but that makes them wasteful in summer, both days of it, so if you think the compressor type needs some heat it is better to add a separate heater.

My wooden framed and clad shop (10'9" x 6'9" external) has 50mm of glassfibre between the 50mm frames, walls and roof. East Anglia, UK, location.

In 14 years, no problems with condensation or rust.

When frosty, outside, a 60W tubular heater under the steel fitting bench keeps things cosy.

Definitely insulate well, and if cold outside, apply low heating, is my advice. But do allow ventilation near floor level to allow any damp air to escape, (Need not be a huge vent, just cover with mesh to exclude spiders, flies, mice etc)

Howard

+1 for Celotex insulation. I converted my single garage & fully lined the walls & roof with Celotex sheets, covered with 12mm OSB/plasterboard, works very nicely. For really cold days I have two small oil rads which after about an hr has the garage nicely up to approx 16* C... cozeeee; when I'm not in there the temp remains around 6-8 *C

​George.

Same experience as Mechman with a very similar solution. I have a small balanced flue gas heater (it was going spare), so temp very rarely falls below about 8C and it warms up in no time. No rust problems.

However SWMBO is about to but a dehumidifier for drying clothes in the house, what's the pros and cons of absorbtion vs compressor?

I have a friend who has just solved the roof element of this problem. His workshop is in a detached single garage with a cenent/asbestos type of roof (as mentioned by HowardT). It dripped badly and the whole place was a rust-generating environment. He has just replaced the roof with a proprietary product consisting of panels which have a ribbed metal outer skin, a thick foam layer, then a ribbed metal inner panel. The roof is now leak-free and doesn't drip. Instead of insulating the walls, he runs a small tubular heater all the time. Seems to work. One benefit being that the workshop is never chillingly cold. The roof was replaced in a day or so, and the panels seem easy to work with. They look the same as the panels used on many newish industrial buildings. Not cheap, but good things seldom are.

If it was my workshop, I would insulate the walls. Speaking from experience of two previous detached workshops, insulating the walls and ceiling (or roof) makes a huge difference. I had a large garage-sized wooden workshop which was lined and insulated with Celotex. Then I had a small detached single-brick outbuilding which I strapped and lined, insulating with rock wool. I also installed a night storage heater in that one, and I could run down the garden and stand in my workshop at any time of the day or night, with the temperature at a constant 64 degrees. Not even a hint of rust. Joy.

Marcus

However SWMBO is about to but a dehumidifier for drying clothes in the house, what's the pros and cons of absorbtion vs compressor?

Duncan,

Meaco do a comparison, but the guy is ever the salesman. He started out by selling the desiccant type of machine and pushed their positives. Didn't (I think) ever mention that any rise in temperature automatically reduces the humidity (provided there is not already large surface areas of damp/wet materials/surfaces).

If it is over 20 degrees Celsius, I would think the compressor type are cheaper to buy and run - while they remain gassed up properly. The desiccant ones will, of course aid the drying, with the extra heat, but only useful if the laundry drying is in a small isolated room. The desiccant type break down mainly because of the cheap carp chinese lubrication or the element fails. One of mine tripped the circuit breaker in the consumer unit (so I carefully removed the offending element!) and the other had failed due to dried out 'lubrication'. Both were an easy fix, although they are a bit of a nightmare to rebuild the first time (first was a basket case, but all bits were present).

No dehumidifier is a cheap to operate. A heat pump tumble dryer might be a better choice for drying clothes.

The compressor type are all basically a heat pump (and fridges are pretty reliable), but the cheaper end of the dehumidifier market is likely a bit of a minefield where longevity is concerned, IMO. I wouldn't consider buying a cheap compressor type.

I bought a dehumidifier when I had an incoming main water supply leak in the house and a wall got damp. I ran it for months and was still taking three litres of water a day from it when the damp wall was no longer showing a reading on a damp meter. I think the above comment re dehumidifying the UK rings true. My workshop never suffers from any condensate or damp problems due I think to three things. The roof is full height of the house so a big area. Up and over doors are wooden. I run a fan through the colder months to keep the air moving around. My winter workshop heater is a diesel fuelled ex truck "Eberspacher" heater that uses its own fan to distribute the heat.

Fact - Every last penny-worth of heat paid for is lost to the atmosphere.

Fact - insulation, properly fitted/applied reduces the rate of heat loss (and therefore the amount of heat required to maintain a given temperature, thus reducing running costs).

Fact - Insulation, without heat input, will not warm anything.

Fact - If temperature drops below the dew point, condensation will result and water vapour in the air will settle on cool surfaces.

Fact - Dehumidifiers reduce the dewpoint temperature, but may not increase the temperature (proper sizing is important).

Fact - Air changes (draughts or ventilation) will increase the cost of running a dehumidifier (unless the outside air is drier than that inside!).

The above make it abundantly clear that a warm, dry, draught-free atmosphere is the requirement for avoiding condensation. Rusting will take place veeerry slowly if water vapour, oxygen and steel are present and it is accelerated by increased temperature, but condensation of water vapour onto the surface will increase the rate of rusting by several orders.

Insulation is an up-front cost, but heating costs are on-going. It is common sense to insulate our houses rather than face huge heating bills, so the same can beapply for heating a garage or workshop. It is likely very much more environmentally friendly too, to insulate rather than use far more electricity (high grade energy) to achieve the same result.

Thanks to all who took the trouble to post advice, I think the answer for me is the insulation one, I take the point about de humidifing the whole of the UK, I have tried draughtproofing the garage with limited success and none of my workshops are heated, my lathe and millers are in the house just a shaper in garage so as I say insulation is for me

Thanks Mick

I'd never even heard of a heat pump tumble drier, but it looks like a good idea which I will research further, I'd already dismissed condenser driers as they must release air at above ambient temperature (or the heat exchanger wouldn't work) and 100% humidity, so instant condensation. According to the manufacturer's claims, all that comes out of the heat pump drier is liquid water (and dry washing one hopes). Happy days!