Sheds and condensation avoidence thereof

But you may need to provide some ventilation and regular airing for those covers to avoid mildew, mould etc.

It might be that the relative constant cool is actually better than climates and situations where there are larger swings of temperature.

The fact that you have insulation in there will make a big difference compared to the average shed with none - since it will dramatically slow the temperature slew rate. The vapour control barriers etc usually spoken off are more there to stop interstitial condensation from rotting the structure of the building itself, rather than making any difference to the actual room environment.

Out of interest I will do an experiment and move my thermometer with humidity meter into the non insulated and unheated end of my garage and see what happens. Things don't seem to rust in there too badly - although it feels cold and damp compared with the insulated workshop end.

Nope need to be sorry, its interesting to hear what happens in varying circumstances!

Wool is the best for 'managing' moisture, IIRC.

PeterC ( snipped-for-privacy@homecall.co.uk) wibbled on Friday 21 January 2011

I saw it claimed on a website selling irish wool for roof insulation - basically the claim was it lessened the risk of rot in timbers by buffering some degree of moisture before it condensed out elsewhere. Could see a reason to disbelieve it - though it wasn't stated exactly how much water a given amount of wool could absorb whilst remaining dry to the touch at various temperatures (if temperature has any bearing).

Mind you - my BCO still wanted the usual ventilation paths and spacings when I was discussing the possibility of using wool...

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Thanks for that John - the apology was directed at the OP really as one of the headaches of T'web is that there is often enough conflicting advice, and trying to sort the needles from the straw can be tiresome to say the least.

I think your comment about the constancy of temperature may be a valid one in that there is then not a wildly varying humidity level, and then as the year goes through, the average temperature of the area involved increases and decreases slowly.

My workshop is relatively air tight so as insolation raises the temperature there is not in ingress of moist air to match this rising temperature, and hence cause condensation when it cools in the evening. That's a possible theory anyway !!

Rob

Very approximately, the number of grams of water per cubic metre in saturated air is the numerical equivalent of the temperature: at 15 degC the air can hold 15g of water per cubic metre.

Let's say your shed has small swings in temperature, from say 6 degC overnight to 10 degC during the day. If the humidity remained constant at 50 percent, then even if the machinery remained at 6 degC because it warmed up slowly, there would be no condensation as then the dew point at 10 degC and 50 percent (relative) humidity is 5 degC:

The air is 50 percent saturated (50 percent RH at 10 degC); and 50 percent of 10 grams (saturated air at 10 degC) is 5 grams. but 5 grams is enough to saturate air at 5 degC, and so 5 degC is the dew-point.

If, however, the temperature swing was from 6 degC overnight to 13 degC all at 50 percent RH, then the dewpoint would be 6.5 degC and condensation would take place.

TF

How do you justify your assumptions?

Suppose your shed begins its day at 6 degC and is full of 50% RH air (and therefore contains about 3g of water per m3), and suppose further that by the early afternoon it warms up to 13 degC. This warming up is going to reduce the RH of the shed air (to about 23%), and then by the time it cools down to 6 degC again, the RH will have gone back up to 50% (and hence still be non-condensing).

The only way to increase the 13 degC RH to 50% would be to add water to the shed air. Where is this going to come from?

OK, so there could have been a change in the weather, increasing the outside RH, and if the shed has been in use, with doors/windows wide open, then the shed air would become well enough mixed with outside air to be indistinguishable from it. But if the shed has remained closed, and its structure and windows/doors are reasonably well sealed, the absolute (not relative) humidity is going to remain constant at 3g/m3.

I thought humidity worked like this until I bought a weather station having an external temperature and humidity sensor. I found that the humidity stays remarkable constant.

There is reason to suppose this is the case, as other postings in this thread have shown concerning placing tools in mighty wooden cases acting effectively as a humidity sink. Wooden floors, benches, cloth items, and other furniture will add to this. But this works two ways, if the humidity starts to fall as the temperature rises, the items acting as a humidity sink will start to lower their water content towards the new equlibrium value and tend keep the shed atmosphere in equilibrium.

And the presence of a human being in the shed is going to be a disaster. Let's say it's the size of a garage, 2m x 2m x 6m or 24 cu metres. At 50 percent RH and 12 degC (robgraham's figure) this garage/shed will hold 6 x 24 = 144 grams of water. Two hour's work by an occupant will add about another 100 grams (figures from a scientific paper) from respiration and sweat, for a total of 244g or just over 10 g per cubic metre. The temperature of the shed will only need to fall to 10 degC, a mere 2 degrees, before reaching the dew point, if the items acting as a humidity sink don't absorb the surplus fast enough. Three hour's work and there's every chance of condensation, unless all that wood can take up the increase.

The only type of shed that won't have items acting as a humidity sink will be metal or glass ones, and they are notorious for condensation problems.

TF

Kipper at sea wrote in news: snipped-for-privacy@37g2000prx.googlegroups.com:

,,

Sorry for teh slow reply ... been away, thanks very much for the tip, was going for all wood in any event but nice to see teh confirmation

Kipper at sea wrote in news: snipped-for-privacy@37g2000prx.googlegroups.com:

,,

Sorry for the slow reply ... been away, thanks very much for the tips, was going for all wood in any event but nice to see teh confirmation

robgraham wrote in news:6752f06f-5583-4ef3- snipped-for-privacy@l22g2000vbp.googlegroups.com:

I'm actually moving the layout from a very unsealed garage and never had any problems there! Really was concerned about moving it somewhere with less ventalation and so forth ...

... and of course a lot warmer for me :-)

fred wrote in news:f58fc5e0-a48a-4e5f-99a9- snipped-for-privacy@k42g2000yqa.googlegroups.com:

very cool idea, I can put a wire frame around it for support, think I'll go with that, thanks