Damp issues and heating a shed.

[Bazz4CQJ]

Originally Posted by M0ALK Richard

If all else fails I would consider sealing individual items in plastic bags with a sachet of that stuff that absorbs moisture whose name I have temporarily forgotten. Silica Gel??

Better than ordinary plastic bags are those which have a metallised coating - like crisp bags - and which are much more effective at keeping water vapour out. You can use either silica gel as desiccator or molecular sieves; both can be recovered by baking them out periodically.

B

[Lloyd 1985]

Originally Posted by merlinmaxwell

Studs!

Thanks for clearing that up! It had been bugging me all day, a case of 'I'm sure it's not that, but I can't think what it actually is right now'!

The Consort Frost fighter that Pete has looks the same as the heater I have, except mine's green and labelled 'Parasene'. Very good heaters! Only had to strip down the motor twice to clean it up and re-lube it as it was getting very noisy.

Regards,
Lloyd.

[Zelandeth]

One thing to keep in mind is that the newer dessicant dehumidifiers tend to work more effectively at lower temperatures than the old refrigerant based ones, and are effectively frost-free as they never chill any component below ambient. They also chuck out a good deal of heat.

Watch the running costs though - the one we have pulls the best part of 1kW at full chat. It does pull an astonishing amount of water out of the air though even in a notionally dry room.

In a relatively draught free space though I can't see you needing any other heat.

[G6Tanuki]

Wide, rapid temperature swings of the air inside a shed are to be avoided: possibly the worst situation is when there's been a cold period for a few days, then the sun comes out!

In an uninsulated shed, the stored contents will be cold. Then the sun comes out and the temperature of the walls/roof shoots up to 20-30 degrees - which drives absorbed moisture out. Some moisture will leave to the outside, some will be driven inwards - where it meets the cold shed-contents and condenses on said contents as dew.

Then when it goes cold again - particularly on a clear night - the roof of an uninsulated shed rapidly drops to a temperature below that of the air - condensation forms on the inside of the roof. Drip... Drip.... Drip.

[It's quite disconcerting to open the door of a condensation-roofed shed and hear a sudden rush as thousands of condensation-droplets all fall at once because of the air-disturbance you've caused].

Insulate, and dehumidify - they're the 2 important things [and *don't* store anything valuable in a steel shipping-container over the winter: a friend lost around £10,000-worth of classic-car parts to rust and mould that way!]

[dseymo1]

Quite a lot of groceries (e.g. frozen peas, instant coffee) are now supplied in zip-lock plastic bags. These seem ideal for protecting small parts from condensation, particularly if as much air as possible is excluded.
I wonder if the larger 'vacuum bags' sold for storing clothes would serve a similar purpose for larger items?
Between these two, it's worth noting that oven cleaner sold by pound shops and the like is perfectly effective (it's a thickened sodium hydroxide solution), and more importantly comes with a large zip-lock bag, intended to hold the shelves etc. I usually apply the cleaner directly to the shelves and save the bag for storage!

[russell_w_b]

Would there be any advantage of building a shed within a shed? My shed (general storage) is the size of a small scout-hut, unclad uninsulated wooden walls, wooden roof inside and corrugated tin sheet roof outside. Solid concrete floor. The bits and pieces of radio, telephone and electronic / electrical stuff within don't seem to have suffered unduly (I use a lot of those plastic storage tubs with lids) but I daren't keep AVOs or anything similar in there.

I considered building a smaller shed-cum-workshop in a corner within, either single-layer breeze block or double-skinned wood and insulating it with Kingspan and putting a flat insulated roof on it, hoping this might keep temperature control and damp to a manageable level. Would this work? The only outside wall would be the shed-end, where the windows are, so three sides would be new and the fourth side part of the existing shed.

[Peter.N.]

That's virtually what I did with mine. The main building is a pre cast concrete garage that I bought for very little money, I divided it up to give me a 'warm' area at the far end which I insulated as my previous post, and used the outer area for storage. The workshop section was always warm and dry but not unfortunately the outer part although its fine for storing less vulnerable things.

Peter

[Hunts smoothing bomb]

I have a 16' x 9' timber workshop that I built around 5 years ago it is just insulated with 25mm Celotex and then hard boarded over.

I have a 1kw/2kw HMV fan heater in use when I am out there and no heating when I am not.

I run a £70 dehumidifier bought from Homebase years ago which is piped to the outside so it doesn't require frequent emptying.

The dehumidifier does not use very much electricity at all, 170w max when the compressor is running otherwise 20-30w for just the fan that recirculates the air.

I have never had any corrosion problems with tools and the place heats up very quickly too when you flick the heater on as the air is dry.


Cheers

[Bazz4CQJ]

Of course, the other problem with sheds is mice. I just went to get my garden blower/vacuum from the shed and the little sods have eaten the plastic petrol priming bulb on the carb. What's left is very soft rubber, so it hasn't perished .

[Phil G4SPZ]

Indeed. When I dismantled my old shed, I discovered that mice had gnawed their way in, nibbled through the back of an old chest of drawers and built a nest. I never knew they were there, as they must have kept as quiet as... mice

[stevekendal]

Update. The Wife bought me a small dehumidifier for Xmas and so far with just a bit of draught-proofing the door, everything seems fine. Weather has been relatively warm though

[cheerfulcharlie]

I use to wrap things in supermarket bags for archiving in the shed.
However found after time these bags do indeed disintegrate and fall apart.
..So much for all the 'green' nonsense being spouted these days that they will last a hundred years or more.

[Phil G4SPZ]

Originally Posted by stevekendal

...The Wife bought me a small dehumidifier...

Lucky you! My wife only bought me socks... so I bought my own dehumidifier last week, one of the small Peltier-effect models that consumes 60 watts. So far, its tank is one-third full.

[stevehertz]

I have a double size garage/workshop built from concrete panels as my workshop. I too suffer from damp and heating issues. Having given it considerable thought, I have come to the conclusion that the only choices you have are two; all or nothing. So, at great expense you can insulate and heat, or you accept the conditions and work around them. I take the latter. I make sure that tools have a vague smearing of oil on them courtesy of an oily cloth, and that anything that I don't want deteriorate is not left in there for long periods, especially during the colder, wetter months. When I'm in there working I have a calor gas heater that quickly gets the place nice and warm. That's it, I know the limits of my workshop wrt damp, and I work around it.

[mark pirate]

I have a calor gas heater that quickly gets the place nice and warm.

These are probably the worst thing to use, they give off water vapor which will add to the humidity of your workshop!

I use a small woodburning stove, these give a good dry heat and help keep the damp at bay.
I also run a medium size dehumidifier during the winter months which again helps keep the damp at bay.

Mark

['LIVEWIRE?']

In my cellar workshop I use an electric panel heater, and have in the past used fan heaters, but damp is still a problem.

[Hunts smoothing bomb]

What works for some doesn't work for others I guess. I do not have the room indoors for all my collection and so a lot of items including expensive test equipment live out in the shed permanently and so for me insulation and dehumidification was a must.

Also remember that when you burn gas, paraffin or any fossil fuel unflued to the outside you produce moisture and lots of it, burn a pint of paraffin and you will release a pint of water into the air.

Cheers

[Nickthedentist]

Originally Posted by 'LIVEWIRE?'

In my cellar workshop I use an electric panel heater, and have in the past used fan heaters, but damp is still a problem.

Don't forget that warming things up will prevent the water vapour condensing on cold things and causing rust etc, it will not actually remove the water from the air. This is where a dehumidifier comes into its own.

[HamishBoxer]

Parafin and bottled gas is the worst sort of heating as it causes mega humidity. Economy 7 and a small storage heater is good alternative and of course the whole house switches to cheap rate for 7 hours at night. That is what we use here. Washer etc all goes on at night.

[mhennessy]

I also live in my cellar, and have learnt over the years how to manage humidity.

The first point to make is that humidity is not a problem in itself. However, condensation is.

For a given air temperature and a given relative humidity, you need to know the dew point. Anything at or below this temperature will cause the moisture in the air to condense upon it. That's why a glass containing a freshly poured cold pint will be wet on the outside.

Stating the obvious, probably, but before I moved into a house with a cellar, I'd never had to seriously think about all this.

The next topic is ventilation. The previous owners of my house had totally blocked up the ventilation. As a result, the cellar was more humid that my humidity meter could measure! The smell of damp was overwhelming. Basically, it was horrible. So the first thing I did was open up the ventilation again, and pretty quickly all was well. The humidity levels were really quite OK, and it seemed like the cellar might be a viable workshop after all...

But then summer happened.

Now, cellars are cold. They are unheated, and a lot of the masonry - perhaps all - is in contact with the ground. What happens in the summer is that the relative humidity shoots up. Increasing the ventilation further still doesn't help. What is going on here?

Take a volume of air at a given temperature and a given relative humidity. Cool it. What happens to the RH? It goes up!

Again, is this stating the obvious? This time, perhaps not. Certainly, I didn't know this, and I had no reason to do so, so I don't feel ashamed at not knowing this. Most others I talk to say the same - but a small minority look at me as if I'm an idiot (they're probably right!). Well, anything is obvious if you already know it!

So in the summer, the warm air comes in, is cooled, and is therefore very humid indeed.

In the summer, you need to dehumidify. Mine runs 24/7. It consumes about 300W when the compressor is running. Tough! It's either that, or not have a workshop! The waste heat goes towards heating the space, which helps to reduce the RH as well.

But now we should think about all that lovely ventilation. In the summer, the ventilation is actually a problem, and of course, you are trying to dehumidify the planet! So you're actually better off blocking it up (not completely, but nearly) - as counter-intuitive as that seems.

In the winter, ventilation helps because the air outside is cooler and drier most of the time. But too much means that your heat is being lost. Finding the balance is the challenge, and it varies with the weather.

No ventilation whatsoever is a bad idea because damp smells start to become noticeable. But when it's freezing outside, I will block up the back to eliminate the risk of burst pipes, etc (must get round to lagging them all).

The other problem with a cellar is moisture ingress via the bricks, and via the floor. These will be wet - there is no point fighting it. Moisture in the earth is obvious - depends a lot on weather and water table - but condensation is responsible for a lot of it. The groundwater will make the bricks cooler, making them attract condensation! Basically, damp/wet bricks aren't a problem in themselves, provided no mould is growing on them (limewash helps here). But it does limit what you can install in terms of shelves, etc...

Back to sheds, all of the above applies.

The problem with sheds is that they are far from airtight, so you are at the mercy of the weather. Great in the summer, of course!

Before you think about heating/drying, you really have to make them air-tight (and then provide the amount of ventilation you actually want). This means adding vapour barriers on the inside of the insulation. Then you can dehumidify the air inside the shed without having to fight with the air on the outside.

For heating, electric is far and away the best (unless you're able to extend your domestic heating out there - unlikely in most cases). Dry heat is what you need. Burning gas produces 4-5 times as much water as gas produced, and is guaranteed to cause destructive condensation.

It's also best to try for a constant temperature. If you arrive in your shed and apply 3kW of heating to rapidly change the temperature for a couple of hours, it might seem very comfortable, but in that time, the objects in there won't have had a chance to warm up - especially the old "boat anchors" that we're all so fond of. So these items will likely be below the dew point, and will therefore attract condensation. Far better to use constant background heating to keep the shed at 10 degrees or above - and boost it to 15 or 18 when you need it. Just a few hundred watts could be enough when combined with good insulation and no draughts. Use "solar gain" where possible (i.e. large south-facing windows with dark blinds - also fit white ones for use in summer).

The same applies for concrete structures (my garage is one of these). However, external insulation is the answer for these because then the thermal mass of the concrete panels will help to smooth over the changes in temperature. My garage is ugly, so I plan to clad it in timber so it looks like a giant shed. I'll have a 2" gap to fill with insulation. It should work well, but the biggest challenge will be the door. Ideally I should replace it with an insulated version, but just sorting out the draughts will make a decent difference. Besides, the garage is for woodwork, which needs less heat than an electronics workshop where most of the time you're sitting still...

So, in summary:

1. Get an LCD thermometer that reads humidity as well. Preferably one that also shows dew point. I have a couple of these: http://www.amazon.co.uk/Extech-Instr.../dp/B000BF0ZTU (they were cheaper when I bought them, but still worth having).
2. Get an infra-red thermometer so you can quickly see if walls and objects are below the dew point indicated by 1. Periodically available at the German supermarkets for around a tenner, and so useful for general workshop use...
3. Use only dry heat. No gas, and no tumble driers (unless the condensing type).
4. Seal the structure and take control of the ventilation. But don't forget about the fumes from soldering, etc.
5. Dehumidifiers are an essential purchase. In fact, most domestic homes benefit from them, although not many people realise this. Because of the air leaks between my cellar and the upstairs, my dehumidifier does in fact reduce humidity throughout the whole house. Win-win!

Sorry to have rambled. It's stuff I've said elsewhere on this forum and others, but it's not always easy to find in a hurry. I'm about half-way through writing an article about my cellar workshop which will cover all this, saving much typing in the future

Cheers,

Mark