# High Humidity...dehumidifier or vents??



## antihero (26 Nov 2009)

Hi Guys,
I know its been done to death but...
I gotta 8 x 15 timber shed/workshop with good insulation but I got humidity readings in the high 80's.Have done for the last couple of months.
Whats the best way of dealing with this,dehumidifier?......some people say thats pointless unless you completely seal your area....not really an option as you gotta open and close your door??right??
Also been told to add vents to the shed......can't understand how that'll help as I already have a healthy 1-2 inch gap at the bottom of my door.
Surely with the damp weather we've been having all vents will do in is pull damp air in and out.
I don't heat the shed unless its Baltic even then only until I heat up then I switch it off(oil filled radiator).
I'm not getting any rust problems at moment but I do build and repair guitars in my spare time so this high humidity is of concern.
Any thoughts most welcome.
Cheers.


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## Digit (26 Nov 2009)

A dehumidifier will both reduce the humidity and add some warmth to the shop as opposed to cold air ventilation at this time of the year. 

Roy.


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## ike (26 Nov 2009)

If you can afford it, get a split air conditioner. Up to 3kw heat output (or 18,000BTU in cooling mode) for 1kw power input. Also works as a dehumidifier.

I self-installed one two years ago. I spend many more hours in a toasty workshop through the winter than I ever did before.

My workshop is 3.5m x 7.5m x 3m - costs around 15p/hr to heat.


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## agbagb (26 Nov 2009)

This may sound strange but it could be all the insulation that is the problem, if as you say it hardly ever heated.

It will stay cold in morning when its warming up outside. Warmer air outside will pick up moisture and blow in under your door. Its then going to cool down in there and deposit the moisture.

Check the internal and external temperatures in the mornings.

A solution could be to give it a quick blast with the radiator on a timer in the morning. Just enough to make sure the inside isn't the first place moist air can get to it's dew point.

Could be worth a try first?


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## MikeG. (26 Nov 2009)

Time for a bit of analysis before you rush off to the solution.

Given that the air outside is rarely at 80% humidity, there must be some reason why you are getting such readings inside. There is damp getting in.

What is the construction of the shed? What are the ground levels like inside compared with outside? Does anything leak? Have you got stored water inside? What are the activitie and occupancy rates of the shed? If you aren't getting rust, are you really sure that you are actually getting 80% humidity (which I would expect to rust everything in sight)?

I hate de-humidifiers. I'll say that now for the avoidance of doubt. They simply mask a poorly designed/ built/ detailed building. Get the building right and you simply won't need one. To my mind, they are for emergencies only. Furthermore, they are hideously wasteful of energy.

If the air outside is less than 80% humidity (which it is almost all of the time), moving that air through your shed will dry your building down to the ambient humidity levels.

So, lots of questions to answer and thinking to be done before you go off and buy a fridge without a door...... the essence of what a dehumidifier is. 

Mike


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## agbagb (26 Nov 2009)

I agree with Mike outside in winter the humidity levels shouldn't be 80. But take a reading at a ground level ground level in the morning (when you get dew on the grass ?). So if the outside air at say 10 degrees C with 50% moisture. Then blow it in to a cold room cooling it to 0 degrees C. The relative moisture would be about 100%.

The case in point here could be somewhere in between.

Agreed more investigation is needed.


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## Digit (26 Nov 2009)

This is a question before someone jumps all over me!
How much moisture does an adult male exhale in a given time period, would that account in part for the high readings?

Roy.


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## RogerS (26 Nov 2009)

Digit":2ctrthsx said:


> This is a question before someone jumps all over me!
> How much moisture does an adult male exhale in a given time period, would that account in part for the high readings?
> 
> Roy.



Depends what you're getting up to, Roy :wink: 

Mike....what would you say was an acceptable humidity range in a workshop?


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## Digit (26 Nov 2009)

Not in my woodwork shop Rog! :lol: 

Roy.


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## agbagb (26 Nov 2009)

Good point, it depends on how hard you're breathing. And in the cold you can see it so 100+ % humidity. However to raise the overall humidity the ventilation would have to be less than the amount you are breathing and not condesing on cold surfaces.

I supose you have to be careful not to breath on the meter when taking the readings.


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## Sgian Dubh (26 Nov 2009)

Mike Garnham":124p2ygh said:


> ... the air outside is rarely at 80% humidity, Mike



Where are you getting your figures from Mike? Outside air in the UK is quite commonly at an average daily RH of 80% or more. My own readings tell me that average daily external RH values exceed 80% from mid-October to the end of February most years-- the number is actually closer to 85% than 80% in December and January. From about the end of February the values gradually lower to just over 70% RH in July and August. I am in Leeds, West Yorkshire.

Some time ago I sourced daily average external RH readings from the Met Office for London gathered over the period from 1955 to 1990 (I think without checking). Their records show a similar RH pattern to my own readings. I imagine readings from a coastal location, particularly on the west coast, will show higher numbers than either of my sets.

The accuracy of the figures I collected, sourced and referenced were important to me because they are used to illustrate points in an academic manuscript on timber technology I've nearly completed. Slainte.


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## antihero (27 Nov 2009)

Thanks for the replys guys.
I'll take a few readings in the morning and let you know what i find but I can tell you were I live (North West,N.Ireland) the humidity is bad most of the time.
Check this out for readings RH for Belfast and I live much further to the North West coast.
http://www.bbc.co.uk/weather/world/city ... t=TT003750

If it is the case that my outside RH is about the same is a dehumidifier my only option??

Thanks again.


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## antihero (27 Nov 2009)

Just checked the weather forecast for my area tomorrow,heres the RH predictions....
9.00 a.m - 84%
12.00 a.m. -78%
15.00 - 79%
18.00 - 94%
21.00 - 96%

Me thinks I live in a very damp area!!


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## MikeG. (27 Nov 2009)

Sgian Dubh":1nz97s0a said:


> Mike Garnham":1nz97s0a said:
> 
> 
> > ... the air outside is rarely at 80% humidity, Mike
> ...



This is what happens when you rely on your memory rather than checking facts. You are, of course, completely right. In my part of the UK, average relative humidity is at or just over 80% for about 4 or 5 months of the year (well below that in the middle of summer, at its highest in the middle of winter).

That doesn't change the principles of my argument, though. 

I haven't time to write an essay this morning, but will simply say that if you choose to install an expensive and power hungry de-humidifier, you must seal up the shed completely, otherwise you will be trying to remove the moisture from the atmosphere of all of the UK. A cheaper and better solution could be a low level vent at one end of the workshop, and a high level bathroom-type extractor fan on a timer at the opposite end.


Or you could raise the temperature a tad by linking, say, a 100 watt light to a thermostat set to, say 8 or 10 degrees.

None of this obviates the need to check that your structure isn't damp. If you have a concrete floor, for instance, lay a sheet of plastic on it for a few days.

Mike


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## woodbloke (27 Nov 2009)

Could someone please elaborate to a numpty(me :roll: ) on this sort of stuff? I thought RH was higher in the summer rather than winter as warm air can hold more moisture :? 
My 'shop is sealed and insulated and I have no problems whatsoever with rusticles on anything. It is dehumidified though (set on a low setting) 24/7 in the summer and a timer in the winter - Rob


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## MikeG. (27 Nov 2009)

Rob,

*relative* humidity is the amount of water vapour that the air is holding compared with how much it can (max.) hold *at that temperature*.

Absolute humidity better describes what you are talking about. One can easily have high absolute levels of humidity but quite low relative humidity levels, if it is very hot..........and low absolute levels yet high relative levels if it is very cold.

Relative humidity is the important measurement, because it better describes how close you are to getting condensation.

Mike


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## Sgian Dubh (27 Nov 2009)

Mike Garnham":1w2eq0a1 said:


> ... That doesn't change the principles of my argument, though. Mike



Mike, I wasn't questioning your other points. They are out of my area of expertise anyway; but I was curious about the RH numbers and where you got them from as they didn't match what I know. Slainte.


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## agbagb (27 Nov 2009)

I think my head has been clouded by relative and absolute as well. I know what they mean but now I'm not sure of the effects. 

Am I right, Absolute Humidity is often higher in Summer (e.g. on a hot day after rain)?

Timber acclimatises to the surrounding conditions, would that be RH or absolute?

How does temperature affect the moisture level in timber?

I's it better to warm the wood and not the air? Is Infra red heating going to be more efficient than convection?


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## MikeG. (27 Nov 2009)

Sgian Dubh":35dkbl3y said:


> Mike Garnham":35dkbl3y said:
> 
> 
> > ... That doesn't change the principles of my argument, though. Mike
> ...



No, no I knew that! That comment was for the original poster..

Sorry!

Mike


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## MikeG. (27 Nov 2009)

agbagb":ij6tei5v said:


> Am I right, Absolute Humidity is often higher in Summer (e.g. on a hot day after rain)?
> 
> Timber acclimatises to the surrounding conditions, would that be RH or absolute?
> 
> ...



AH can be higher in the summer, certainly, but as I said, I think RH is the more important figure because it reflects the likelihood of condensation occuring.

We are getting to the limits of my expertise here, but my instinct is to keep the building environment as equable as possible, and to condition the wood in the normal way (in the final resting place environment for a few weeks). If you were to warm the wood in your workshop differentially to the air around it that could possibly work, but could also possibly set up all sorts of undesirable moisture movements.

If in doubt, keep things simple!

Mike


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## agbagb (27 Nov 2009)

> If in doubt, keep things simple!



I like simplicity as well. Conditioning in the final resting place is best. 

Problem though. The wood then spends 2 months in the workshop being built in to something, (I'm slow).

Unfortunately the "simple" solution that springs to mind, for most folks, is a dehumidifier. 

Maybe if we had more knowledge (Slainte. will your paper help?) we can come up with easy, practical, cheap, low energy solution.


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## Sgian Dubh (27 Nov 2009)

agbagb":7qma5dcb said:


> I think my head has been clouded by relative and absolute as well.



Atmospheric humidity refers in a non-specific way to water in the form of water vapour in air. Absolute humidity (AH) describes the actual amount of moisture vapour in the air-- another name for absolute humidity is vapour pressure. When air is fully saturated with the maximum possible water vapour it can hold at any given temperature, it is at saturation vapour pressure. Air that has a vapour pressure below the saturation vapour pressure is able to carry more moisture.

Relative humidity therefore is the ratio of the amount of moisture in the air to the maximum amount of moisture that the air can carry at a given temperature X 100, which describes RH as a percentage of AH.

Warm air can carry more water vapour than cool air. For example, 1 cubic metre of air at 35ºC can carry a maximum of 39.54 grammes of water vapour-- the air is fully saturated, ie, it is at saturation vapour pressure: the relative humidity (RH) is 100% and the vapour pressure or absolute humidity (AH) is 39.54 grammes of water vapour. For comparison one cubic metre of air at 15°C can only hold 12.82 grammes of water vapour.

Dew point is the temperature at which water vapour condenses out of air. For example, if fully saturated air cools by even 0.1ºC the gaseous water in it starts to condense into liquid water. This is essentially what happens when the bathroom mirror ‘steams up’ as you take a shower. In this case warm, saturated air hits colder glass, it cools, and this causes the water vapour in it to condense on to the glass.

In the UK house interiors experience lower RH values in the winter than they do in the summer. This is because we heat our houses in the winter. At this time of year fresh air that enters the building through vents, and natural cracks and crevices, is comparatively cold.

Cold air cannot carry as much water vapour (WV) as warm air. Air at 5ºC can carry a maximum of 6.79 grammes of WV per m³. Outside air at 5ºC fully saturated with 6.79 grammes of WV/m³ brought into a house and then heated to 20ºC without adding any more water vapour to that package of air results in an RH of 39.29%. At 20ºC air can hold a maximum of 17.28 grammes/m³ WV. To work out the RH value of the heated air calculate, Absolute Humidity of the air / Fully Saturated level of the heated air X 100. For the parcel of air just described therefore we ascertain the RH percentage as follows: 6.79/17.28 X 100 = 39.29% RH.

In British summers internal RH values are higher than winter RH values. Temperatures are warmer and the outside air is able to carry quite large amounts of water vapour (WV) leading to raised AH values. Open windows and doors let a breeze through the house which brings in water vapour and causes relative humidity within buildings to more closely match external relative humidity.

The above isn't a full explanation, but hopefully you can get the general gist of the subject. Slainte.


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## agbagb (27 Nov 2009)

Wow, thanks, proper knowledge. I'll let that info sink in for while.

Meanwhile, does anyone know how timber moisture content relates to RH and AH.

I'm thinking wood in modern house 8 - 12%? RH in the house in winter Circa 40%? or is it the AH that matters. 

Cheers
Andy


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## Sgian Dubh (27 Nov 2009)

agbagb":38gv9wye said:


> ... does anyone know how timber moisture content relates to RH and AH.
> Andy



Well, I do in some depth. Unfortunately there isn't the space here to describe all that you need to know in a short post. I guess you'll have to wait for the book on timber technology I'm working on. But a snapshot is as follows:

30% RH = 6% wood EMC (equilibrium moisture content)
50% RH = 9% wood EMC
70% RH = 13.5% wood EMC
90% RH = 20% wood EMC 

These are typical numbers at 20ºC for most wood species. Higher temperatures lead to lower wood MC percentages and lower temperatures cause higher wood MC percentages. Wood density is also a factor that causes variations, as does the wood's structure. 

Also bear in mind that to achieve EMC wood needs to stay in unvarying RH and temperature condition for considerable time. This never occurs in normal circumstances because RH varies diurnally, hourly, and even by the minute and, due to one form of hysteresis, wood does not immediately react to changes in RH. It changes slowly over time. 

Further, wood is seldom the same MC all through and in normal use it has a moisture gradient within it, eg, it might be 14% MC at the core and 10% MC at the shell with an average MC therefore of about 12%. This condition might indicate the wood has fairly recently been moved from an area of higher average RH to an atmosphere that has a lower average RH condition, eg, it's fairly recently been moved from an unheated storage shed to a drier, insulated, warmer workshop.

AH is not really relevant to the situations described above-- it's only relevance is as a function for understanding the subject of atmospheric humidity as a whole, and I have missed out significant factors from this post for the sake of brevity and simplicity. Slainte.


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## antihero (27 Nov 2009)

Thanks for all your replys guys,
me head is spinning a bit with all this RH info.
Took some ground level readings this morning though......
Inside shed was 7.3c/85%
Outside shed was 6.6c/87%.

So,obviously I'd rather not go down the rather expensive way of a dehumidifier,but just can't see no other way of controlling the humidity.
Adding vents just seems to me to be pointless with outside RH being what it is(or am I missing something?)

Thanks again guys.......although still not sure what my best option would be! :?


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## MikeG. (27 Nov 2009)

antihero":2a7lmhl8 said:


> Adding vents just seems to me to be pointless with outside RH being what it is(or am I missing something?)



Yep, you are missing somethinjg!

I described a system that will work.....the forced cross ventilation with a low level vent and a high level fan. Put it this way, it is about a £20 gamble if you buy new, and maybe a lot less than that with stuff off fleabay.

Think of mist. That only exists when the air is still. As soon as a breeze picks up, it disappears. It doesn't get moved somewhere else, it just disappears. I don't know the physics of it, but moving air dries stuff. You can dry clothes on a clothes line in the middle of winter, so long as there is a breeze. 

This is one of the fundamentals of building design......ventilation. It works! It won't work just by having a gap under your door, because where air needs to move it needs an "in" and and "out" path......so if it is going to go out under the door it needs to come in from somewhere else.

I don't want to do the old "trust me, I'm an architect" routine.......but even without seeing your exact circumstances I would be very confident that you will improve matters by following the simple scheme I suggest.

Mike


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## agbagb (27 Nov 2009)

Thanks Slainte.
That's a combrehensive enough answer for me now. Let us know when the book is out.

Mike, I think a breeze helps drying because: If the air isn't moving around a wet object it will fill up with water vapour to saturation and no more will vaporise. If you blow the saturated air away more can vapourise in to the "fresh" air. 

I don't know if you get past some kind of equalibrium of the "fresh" air RH and the dryness of the object though. If that makes sense. 

Antihero, That blows my theory that it could be colder inside the shed then.

Another thought, seal the drafts and put a tray of salt out. We used to do this when we over wintered our wooden chalet in Mablethorpe. We never got any damp.

Andy


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## jimi43 (28 Nov 2009)

This has been a really interesting subject for me as I made an early mistake of putting an uninsulated steel roof on my workshop the summer before last and had an actual rainfall inside in winter!

I have since cured this by insulating the cold metal and putting air vents at the top of one wall where it meets the roof and letting cracks on the otherside create the "in" bit...it works...I agree with that theory...

Incidently...I cut a tree down and left the logs in my car the other day...it took me nearly 20 minutes to get the condensation off of the screen in the morning...now it is coated with sap deposit! DON'T leave new logs in your car...especially pine ones!!

Jim


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## aesmith (28 Nov 2009)

antihero":zvanx4jx said:


> Inside shed was 7.3c/85%
> Outside shed was 6.6c/87%.


Under those conditions ventilation on its own is going to do nothing to reduce the RH inside, unless you have some heat as well. 5 deg temperature rise inside compared to out would drop that to 65% or so.


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## frugal (29 Nov 2009)

Mike Garnham":24lozrle said:


> This is one of the fundamentals of building design......ventilation. It works! It won't work just by having a gap under your door, because where air needs to move it needs an "in" and and "out" path......so if it is going to go out under the door it needs to come in from somewhere else.



How does this work with insulation? You insulate the workshop to keep the heat in, and then drag cold outside air across the room to keep it dry.

I am not saying that it is not the right thing to do, they just seem contradictory for a beginner to this sort of thing.


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## MikeG. (29 Nov 2009)

Good question Frugal!

Every building needs ventilation. In a house, I always use mechanical ventilation with a heat exchanger so that the warmth isn't lost with the extracted air. A workshop is generally only in use for a few hours a week. My suggested scheme could easily be turned off for the time that it is used/ heated to overcome the problem you correctly highlighted. 

For the 90% of the time that it is unheated and unused, the ventilation will be of huge benefit to the internal environment, without costing anything in terms of heat loss.

Mike


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## promhandicam (29 Nov 2009)

Although not relevant for the OP, due to the interest shown in this issue, I thought I'd relate my recent experiences with damp. We moved into our current home in July and discovered that there were some serious problems with damp which involved completely replacing the living room floor - the kitchen and bathroom will have to be done next year. The problems stemmed from inadequate ventilation under the suspended floors and water ingress through the few air bricks that had been installed due to a concrete hard standing having been laid up to the outside wall and level with the bottom of the air brick. Although remedial action has been taken, some of the downstairs walls had am MC 80% and the damp was affecting my asthma. After doing a bit of research on the internet I decided to buy thisdehumidifier and can highly recommend it. The dehumidifier has been extracting 6 - 7 litres a day everyday since starting to use it a couple of weeks ago. It has solved the condensation that we were getting on the windows and toilet cistern and my respiration has much improved. So if anyone is in need of a dehumidifier, for £150 I can certainly recommend the one I've linked to above.

Steve


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## jimi43 (29 Nov 2009)

Have you worked out how much it costs to run Steve?

Jim


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## promhandicam (30 Nov 2009)

Hi Jim.

According to the technical data, the maximum power consumption of the unit is 620W. Therefore if it runs 24/7 at max power in a month it will consume 430KWh. From our supplier this equates to £43. In this case, the unit will extract approximately 200 litres of water. 

The actual consumption will obviously depend on the RH of the property - the unit has a humidistat which on Auto setting turns the machine off when the RH reaches 55 - 60%. We have had it running for 2 weeks now and it has been running more or less constantly although in the last few days I have noticed it is starting to cut out as the RH obviously starts to get down to a reasonable level.

HTH,

Steve


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## antihero (30 Nov 2009)

OK guys,I seem to have really touched on apoint that interests people.
So,this is what I'm gonna do.
Install an extractor van and vent,that will hopefully keep things resonable when I'm not in there.Then possibly get a small dehumidifier and use it when working,if needed.
Would really like to keep the RH down to 50% while I'm working.
Thanks for all your help on this!
Cheers.


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## MikeG. (30 Nov 2009)

Good decision............but don't do both at the same time! 

Mike


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## antihero (30 Nov 2009)

Something like this should be the ticket,what you think Mike?
http://cgi.ebay.co.uk/EXTRACTOR-FAN-KIT ... 2303fb3a5d


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## MikeG. (30 Nov 2009)

Yep, that's the sort of thing.......although I am not sure why it is low voltage.

Mike


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## jimi43 (30 Nov 2009)

WOW that ain't cheap for an average few hours a day merchant! No wonder my leccie bill went up so high!

I must admit I could actually "smell" the dryness...or rather NOT smell the humidity when I did run it...but I felt (as was mentioned earlier) that I was dehumidifying Kent...and probably parts of the North Sea as well...so in a relatively sealed room like a guest room that would work but my shop was not that tight.

This is a really interesting subject though!

I had a discussion with an insulation engineer the other day about the very same thing and my steel roof and he said to put a false ceiling of silver backed plasterboard in...with air cavity openings each end in the cavity and then put a thick layer of insulation on top of the false ceiling...mmmm

More research needed I think!

Jim


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## Digit (30 Nov 2009)

That's a coventional 'cold roof' Jim. Works ok but you could lose a fair bit of head height, depending on how much insulation you install of course.

Roy.


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## jimi43 (30 Nov 2009)

Digit":3qa5izoy said:


> That's a coventional 'cold roof' Jim. Works ok but you could lose a fair bit of head height, depending on how much insulation you install of course.
> 
> Roy.



That was my quandry EXACTLY Roy....it is all a compromise I guess...

I don't think I can afford to lose that height...I suppose I could swing long timber around horizontally instead! :lol: 

So far I have used estate boards (the corrugated plastic stuff used by estate agents) which were free...then laid on a layer of foil foam foil stuff...it seems to work so far!

The bit I haven't yet done is condensing...the other area (most) isn't and if it doesn't do it now with this humidity it NEVER will!

Jim


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## Digit (30 Nov 2009)

The alternative Jim is a 'warm roof', where the insulation goes on the outside of the roof. Ok if the extra height isn't a problem. DAHIK!

Roy.


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## jimi43 (30 Nov 2009)

What would you suggest for the outside Roy...I can't think of what I would use?

Jim


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## chill (30 Nov 2009)

hi all, very interesting
how does a warm roof work, I need to refelt existing roof and insulate roof at the same time, would like to use onduline or similar but need to walk on roof a couple of times a year to cut boundary hedge, is it possible to walk on onduline without damaging it. Maybe will look at some form of solar collector for back ground heat, whilst using Mikes ventilation idea


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## Keith Smith (30 Nov 2009)

I don't normally post here but I have just had exactly the same problem with relative humidity levels at over 80% in the workshop and so have been looking into the pros and cons of dehumidifying a workshop and some of the info in this thread is incorrect.

Ventilation, as has been recommended, will do no good at all unless the workshop is well heated. Otherwise you are just swapping one lot of cold moist air for another. In fact it will cause more problems, as the outside air is likely to be colder than the air inside, and you will end up further cooling the workshop.

Keeping the workshop warm with some ventilation would help but is likely to be prohibitively expensive unless the workshop is very well insulated.

The only practical solution if you want to run your workshop at 60%RH is to get a dehumidifier. The latest desiccant wheel dehumidifiers , like Steve has bought, are the ones to go for as they will work at low temperatures. They do take a fair bit of current; I have an XDry and that is rated at about 700W but it only draws that level of power when it is actually dehumidifying. It spends a lot of time with just the fan running when consumption is very low.

One problem with dehumidifiers is that they will not cope with fine dust as the rudimentary filters are just designed to stop household fluff. If you want to run one in the workshop it should be run overnight when you are not working. This is why I bought the XDry, it is one of the few dehumidifiers that can be used with an external timer. 

Of course all this would be a waste of time unless the workshop is reasonably well insulated and sealed.

Keith


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## Digit (30 Nov 2009)

Oh Lord! I wish I hadn't said anything now! 
The best advise I can give is either ask Mike G or Google for a more complete answer. But basically the stuff I investigated is a cellular foam sandwich with a waterproof outer. 
If you can stand the height gain Jim the cheapest/easiest option would probably be to remove the metal sheets, add further timber to the existing joists then go the cold roof route. 

Roy.


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## Digit (30 Nov 2009)

Don't know anything about onduline Chris so I can't comment. About felt I can. Don't! 
Unless there is some valid reason why not I would go 11mill or 18mill OSB then EPDM bonded on top. The EPDM is totally waterproof, will out last lots of refelting ops and can be walked on. 

Roy.


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## jimi43 (30 Nov 2009)

Hi Roy.....

There is just too much acreage to do that mate...though I should have thought it through first I must admit. When you get 16 foot lengths of flat section plastic coated sttel from a warehouse for next to nothing and the sun is shining it all seems very simple....and it doesn't leak like a seive like the old one... :wink: 

I have to think about the options now I have quite a bit of kit I want to keep....in the meantime I have ordered some more Camelia Oil from Workshop Heaven..(good price that!) and am copiously coating everything metal with it "just in case"!!!!    

Jim


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## Digit (30 Nov 2009)

I don't get the first bit Jim. If you can lift the sheets and place extra timber on top of the existing joists that is the only additional expense to plaster board and insulation surely?

Roy.


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## jimi43 (30 Nov 2009)

AH...well it ain't QUITE that simple....the "lifting the sheets" bit...

I would have to take a picture to show you how....um FRANKENSTEIN...the evolution that is my workshop actually is.

Trust me...lifting the sheets is not an option. :wink: 

J


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## promhandicam (30 Nov 2009)

Keith Smith":3qm14nyu said:


> . . .This is why I bought the XDry, it is one of the few dehumidifiers that can be used with an external timer. . . .



The one I linked to will also work with a timer - it remembers the settings when the power is turned off. It can also be plumbed in which makes it good for a workshop as you then don't need to keep emptying the container.

Steve


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## Digit (30 Nov 2009)

> Trust me...lifting the sheets is not an option.



Sprayed foam?

Roy.


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## jimi43 (30 Nov 2009)

Digit":2e6q68az said:


> > Trust me...lifting the sheets is not an option.
> 
> 
> 
> ...



HA! That brings back memories. Years ago in a cottage I had in Cornwall which was 400 year old and granite walls as thick as Simon Cowell...the damp would ingress via the "pointing" or lack of it into the bathroom

Foam had just been "invented" or become popular and I decided to put a beautiful pine false wall up on battens...and it looked GREAT! THEN I made the mistake of deciding to fill it with expanding foam...

Which DID! BOY does that stuff EXPAND!

You can visualise it can't you?   

My wife said I did a great impression as King Canute!   

After that experience...it kinda put me off of expanding foam for life....

I never have had the guts to try it again...even if it IS pink now!

    

Jim


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## Digit (30 Nov 2009)

I did some of the early product development on the stuff for the motor industry, and boy, did we get it wrong. Canute is about right! 
We were moulding it in slabs in a ply box with one end open, one 100th in the box and rest everywhere! :lol: 
But they have cracked it for roof insulation. 

Roy.


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## jimi43 (30 Nov 2009)

Digit":2d2hw8gj said:


> I did some of the early product development on the stuff for the motor industry, and boy, did we get it wrong. Canute is about right!
> We were moulding it in slabs in a ply box with one end open, one 100th in the box and rest everywhere! :lol:
> But they have cracked it for roof insulation.
> 
> Roy.



The spray stuff interests me..it may very well be the perfick solution my friend! 

Do you know where you get it...do you rent a "gun thing" and how much it is roughly?

I think we may have cracked it!

Jim


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## Digit (30 Nov 2009)

DIY's not as cheap as some of the other methods but you'd save on the plaster board at least. Here's one, there may be others worth following up... 

http://www.spray-insulation.co.uk/

Roy.


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## Keith Smith (30 Nov 2009)

promhandicam":13f8xfc9 said:


> The one I linked to will also work with a timer - it remembers the settings when the power is turned off. It can also be plumbed in which makes it good for a workshop as you then don't need to keep emptying the container.
> 
> Steve



They look almost the same machine, I assume yours also has the natty cycling vent on the front. Looks to be the water collection that is the main difference. I was getting 6 litres per day out of mine until the RH dropped down to 55%. Now I only run it every third night on high and only get a litre out in eight hours. So I seem to have hit equilibrium. Workshop is warmer too, or feels that way now its drier.

Keith


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## jimi43 (30 Nov 2009)

Thanks Roy...I will look into this.

Many thanks for your suggestions

Jimi


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## Digit (30 Nov 2009)

Let us know how you get on.

Roy.


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## promhandicam (1 Dec 2009)

Keith Smith":2lm9xzrq said:


> They look almost the same machine, I assume yours also has the natty cycling vent on the front. Looks to be the water collection that is the main difference. . . .



Yes it does have a cycling vent on the top that can set in various positions. I think the one I have is maybe the latest version of your as mine is also made by Prem-I-Air.

Steve


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## chill (1 Dec 2009)

Thanks Roy, will have to look into this carefully as cost maybe prohibitive, 
footprint of shed is 22 ft x 12ft converted tackroom so larger than your average garden shed . Roof is already fully boarded (timber slats) but existing felt has gone porous  need to insulate roof maybe easier to lay sheets on top? and then felt/epdm/onduline etc


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## Digit (1 Dec 2009)

Check these out Chris. Permaroof do off cuts which are much cheaper than standard. The second link shows how easy the job is, and it is! 
Once stripped the rubber would be down in less than a couple of hours. If you go the wholes hog with felt, three layers, the rubber will most likely be cheaper, and remember, there are no joints. It's the stuff they make inner tubes out of, in fact, if you are unlucky enough to puncture it that is how it is repaired, with a puncture outfit! 

http://www.permaroof.co.uk/ 

http://www.delston.co.uk/

Roy.


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## johnnyb (1 Dec 2009)

sorry but i have not read all the posts yet so i may be repeating someone.
i dry buildings for a living and the best solution for an unheated building in winter is....... a dehumidifier!!! BUT not yer run of the mill refrigerant d hum as these will not work well(or at all) at low temperature as they rely on cooling the air to dew point to work and they tend to ice up below about 10 celcius and this makes them practically useless to the point where they become blocks of ice at 5 celcius. some good ones do have hot gas defrost But they are still inefficient at low temps. ideally they need to run with the incoming air being cooled still to dew point but not to freezing about 15 celcius or so. 
anyway what you need is a dessicant dehum such as an amberdry. this is perfect because....
1 it will work great in very low temps as it use silicagel to dry the air which is not temp dependant(ice rinks are dehumidified with these!)
2 it has a very low setting (about 250w)
3 by its action it also warms the air somewhat
4 it is quite sophisticated for a £200 pound unit and has a humidistat if you want to control the humidity and a condensor which most industry dessicant do not, they just blow the wet air outside. which means it works just like a normal refrigerant and you empty the trayevery few days.


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## jimi43 (1 Dec 2009)

This makes a great deal of sense....thinking back to when I ran the dehumidifier I have.

It was bloody FREEZING when it was running and cooled the workshop to well below the outside temperature! This is pointless as it might have been dry but it was too cold to work in!

I think I will put up with it and stick to Camelia oil.... :wink: 

Jim


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## Freak18 (7 Jan 2010)

As we know that we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is low, we can feel many coolers. Then, it could be just to study the conduction of relatives. Basement Dehumidifier


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## liam8223 (7 Jan 2010)

I have just bought the X-Dry dehumidifier from Meaco.com.

It is a dessiccant dehum, and as such does not freeze at low temp.

My workshop is uninsulated, as its only temporary, and this dehum has transformed the place.

It removes 10 litres a day, and has a tank, same as a normal dehum.

Most importantly it warms the air around 12 degrees warmer than when it enters the machine - very handy for keeping the chill off.

I have no doubt in my mind, that if my shop were insulated it would be quite comfortable in there for short jobs, without a heater.

I can thoroughly recommend this dehumidifier!

Liam.


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