Condensation Problems in Workshop

[Howard LewisParticipant @howardlewis46836]

Condensation will occur when for a given level of relative humidity, the temperature falls below the dew point.

The dew point will vary according to ambient pressure, ambient temperature, and relative humidity.

We demist a car windscreen by blowing warm air over it to raise the temperature, since we are unlikely to be able to reduce the humidity of the air brought in

Recirculating the air, for a quick warm up, is likely to be less effective, since because of the water vapour that we exude, the humidity will increase.

The warmer, fresh, air will absorb the moisture, and the fan will ventilate the interior, by displacing the moist air, minimising humidity.

Mostly, we are concerned with steel which will rust in the presence of water and oxygen.

So the objective is to maintain conditions where the hunidity is low and teleperature is high enough, to prevent condensation.

Dehunididiers reduce the water vapour in the atmosphere, Heaters m(As long as they do not contributen bwater vapour) serve to keep mthe temperature above the dew point.

Small amounts of ventilation will allow moist air (water vapour) to be removed.  You don’t need big vents, just enough to let out the moist air, at floor vlevel, to be replaced by drier air at high level.

A LOT of air will pass through a 13 mm hole, not enough to lower the temperature drastically, but nsuffivient to allow mthe moist air to be replaced.

Most of the time, just removinmg, or rducing the moisture content will mprevent condemsation.

In a former small workshop, without ventilation, the oil sprayed onto the Myford would often be grey as it emulsified. In the present, well insulated, shop, (10’9″ x 6’9″ external) with just a couple of grilled 25 mm holes at floor level, and a weatherproof, cowled, 6″ fan at ceiling level, without heating, in East Anglia, condensation is normally not a problem.

If the ambient is expected to fall ,below freezing, a 80 watt tubular heater under the fitting bench sxerves to keep mthen teperature above the dew point.

The 2 Kw thermostatically controlled fan heater is there for my comfort, and runs very little once the temperature has reached 18C.

Working in a perfectly sealed space will have two effects.

1) The hunidity will rise because of your presence, increasing humidity, emitting moist air as you breathe and perspire.

2) Eventually, you will consume all the oxygen and die.

So, ventilation IS necessary. Not excessive, just enough to keep you alive and humidity below the point where condensation occurs.

Howard

 

 

[Howard Lewis]

On Howard Lewis Said:

Condensation will occur when for a given level of relative humidity, the temperature falls below the dew point.

The dew point will vary according to ambient pressure, ambient temperature, and relative humidity.

We demist a car windscreen by blowing warm air over it to raise the temperature, since we are unlikely to be able to reduce the humidity of the air brought in

Recirculating the air, for a quick warm up, is likely to be less effective, since because of the water vapour that we exude, the humidity will increase.

The warmer, fresh, air will absorb the moisture, and the fan will ventilate the interior, by displacing the moist air, minimising humidity.

Mostly, we are concerned with steel which will rust in the presence of water and oxygen.

So the objective is to maintain conditions where the hunidity is low and teleperature is high enough, to prevent condensation.

Dehunididiers reduce the water vapour in the atmosphere, Heaters m(As long as they do not contributen bwater vapour) serve to keep mthe temperature above the dew point.

Small amounts of ventilation will allow moist air (water vapour) to be removed.  You don’t need big vents, just enough to let out the moist air, at floor vlevel, to be replaced by drier air at high level.

A LOT of air will pass through a 13 mm hole, not enough to lower the temperature drastically, but nsuffivient to allow mthe moist air to be replaced.

Most of the time, just removinmg, or rducing the moisture content will mprevent condemsation.

In a former small workshop, without ventilation, the oil sprayed onto the Myford would often be grey as it emulsified. In the present, well insulated, shop, (10’9″ x 6’9″ external) with just a couple of grilled 25 mm holes at floor level, and a weatherproof, cowled, 6″ fan at ceiling level, without heating, in East Anglia, condensation is normally not a problem.

If the ambient is expected to fall ,below freezing, a 80 watt tubular heater under the fitting bench sxerves to keep mthen teperature above the dew point.

The 2 Kw thermostatically controlled fan heater is there for my comfort, and runs very little once the temperature has reached 18C.

Working in a perfectly sealed space will have two effects.

1) The hunidity will rise because of your presence, increasing humidity, emitting moist air as you breathe and perspire.

2) Eventually, you will consume all the oxygen and die.

So, ventilation IS necessary. Not excessive, just enough to keep you alive and humidity below the point where condensation occurs.

Howard

 

 

So my current workspace is so large and not well sealed that my dehumidifier has little impact. I assume that the dried air is replaced with moister air from outside faster than it can be dried.

The lack of insulation causes big temperature swings, it gets very warm when the sun shines on it and heats the metal, but looses that heat quickly once the sun goes down.

My thinking in making this well sealed, insulated, internal room in the shed is that I can leave the dehumidifier running, and it’s inbuilt humidistat can keep the humidity constant. The better sealed it is, the less often it will have to run to maintain the humidity, increasing the life of the machine and helping with electricity costs. Are you saying that in this situation I should still include ventilation? Surely that defeats the purpose somewhat of sealing the room so the dehumidifier can work?

[Bazyle]

On Bazyle Said:

A dpc on the floor would be fine if you can avoid it being punctured by nibs and specs of gravel that are magnetically attracted to concrete floors. The moisture will be diverted to the edge so be aware of where that is and if it is ventable.
In theory 2in of insulation in an 8×8 foot cube (excluding floor) wants about 100W heating for a 10 degree temperature difference. A 16×8 only needs about 60% more so it is not directly in proportion to floor area.
However I would still go with your idea of 4×1 frame and filling it with insulation but you could make alternate frames of 1/4 ply if cheaper. In the verticals it tends to sag so needs to have the extra frame members to ‘grip’ even they are not structurally needed. Also put in some noggins so it is not a single vertical run. What you sometimes see is builders cramming the insulation in, especially if retrofitting a ceiling from below to make it grip but this defeats the object of having a loose fill with lots of air. It is the air that gives the insulation not the material, even for Kingspan etc. The only time air hasn’t been the best insulator was for the space shuttle.

The dehumidifier may be all the energy it takes but thermal mass of the contents will make a difference to how it feels. A remote controlled switch for prewarming the machines would be the ultimate to prevent your breath condensing on them.

I should say, I only really want this room insulated to avoid temperature swings in an attempt to control condensation, I don’t plan to heat it other than what is provided as a by product by the dehumidifier. Apart from when I’m in it, which tbh with a newborn baby, is not that often atm.

Sorry, I’m not sure I follow you regarding the alternate frames of 1/4 ply. Do you mean I could cut the ply and us it as every other stud? Or something else?

If I laid some 2x2s on the concrete floor, and then placed thick OSB or plywood over them, would the air gap negate the need for a DPM?

[old martParticipant @oldmart]

Insulation is the answer, it slows the changes of temperature which cause the condensation, even in non heated areas.

[John McCullaParticipant @johnmcculla]

Ok, so I think I’m finally settled on what I’m doing.

I’ll build a frame of 2×2 timber for the floor, walls, and roof, resulting in a 12′ x 8′ cuboid. Between the 2×2 timbers I’ll fit 50mm polystyrene boards (https://www.macblair.com/insulation/polystyrene-insulation/xtratherm-polystyrene-sd-eps-50mm.html), and sandwich that either side with 9mm OSB, apart from on the two walls butting up against the walls of the garage, where the corrugated tin garage wall will be the outside wall.

This should leave me with essentially a wooden flat roofed garden shed, inside the garage. I can then run the existing wiring for sockets into the shed, mounting the cables in plastic conduit.

My plan is to run a dehumidifier constantly, allowing it to cut in and out according to it’s inbuilt humidistat.

My only slight niggle of a concern is the fire risk, polystyrene insulation doesn’t seem to have much fire resistance, but then again even if it did, it’s sandwiched between wooden boards which will burn anyway. I don’t see that there’s much I can really do about it, short of building something out of bricks which simply isn’t feasible. Is it safe enough for a workshop? I suppose the dehumidifier is a fire risk too, but maybe it could be run inside a metal cabinet with a vented door? Would that help?

[John Mellor 1Participant @johnmellor1]

I would not worry about flamability if you are not using naked flames. Many countries have timber frame and OSB clad buildings.

If it is breathable…a small vent.. then you will not need to run the dehumidifier in the warmer weather. You will have a cosy workshop.

 

[John McCullaParticipant @johnmcculla]

I know it’s been a while, but what can I say, life has been (and is) busy!

I made one of the long (3.6m x 2.4m) wall frames from 2×2 timber over last Christmas, but haven’t managed anything since. I’ve since realised that since 2×2 timber isn’t actually 2″ thick, that I won’t be able to fit the 50mm insulation within the wall.

So my plan for this Christmas is to build the rest of the walls and the roof from 3×1.5, the floor from 2x2s, and get the shell assembled. I can then put 11mm OSB on the outside of the walls and roof to give it some rigidity, and that leaves me with a usable space while I accumulate the funds to insulate it and then clad the inside (probably with plywood despite the extra cost).

In terms of fire protection, polystyrene sheets seem to have a pretty bad reputation. I’ve seen multiple people online refer to them as functionally becoming napalm once lit. Obviously that sounds bad, but given that if a fire starts it’ll probably all burn down anyway because it’s in the garage and away from the house so I won’t have any warning if it, does how quickly it burns really matter? Or would I be better going with something like PIR, which insulates better, has better fire resistance, but is twice the price. I would appreciate your thoughts.

[Howard LewisParticipant @howardlewis46836]

My shop has 50 mm square timber for framing.

The outer walls are 19 mm overlapped boards.

All walls are exposed to the weather, but the rear wall is protected by being very close to a 2 metre high boarded fence.

Thy inner walls are 12 mm ply. Between the inner and outer, is filled with glass fibre.

The roof is 12mm ply on each side of 50 mm framing, with a rubber outer membrane.

Being fairly small it is cosy, and the 2 Kw fan heater usually runs for less than 15 minutes before the thermostat shuts it down. After that, the heat from the machines, and my body, mean that it only runs for short periods, and 30 – 45 minute intervals.

If frost seems likely, a 60 – 80 watt tubular heater is switched on. Within 24 hours, the steel benches are warm to the touch.

Insulation prevents rapid temperature changes, nearly all of the time the temperature is kept above the dew point. Only when I failed to switch on the tubular heater did i suffer condensation. The heater soon removed that!

The 6″ intake fan is rarely used (The intake is covered by a sloping metal hood, with the lower end below the intake point, so weather (but not spider) proof.

Any moist air exits via the two small floor level vents, and I am unaware of any draughts.

Your inner insulated shop should be warmer and much less less prone to condensation than the uninsulated metal skin garage.

A friend whose shop is a concrete sectional garage, we insulated with a mixture of glass fibre and polystyrene sheet, he has had no problems with condemsation.

Howard

[Master of noneParticipant @masterofnone]

If you are considering a rigid board type of insulation (PIR or polystyrene), I believe it is vital that it is cut accurately into the studwork and it buts hard up against the internal wall lining.  If any cold air can circulate between the wall lining and the insulation, it will defeat the purpose of having the insulation.  If you intend to conceal electrical service behind the wall lining, it will be more difficult to achieve air-tightness.

Similarly, I would recommend against an air gap beneath the floor as it may allow cold air to contact the underside of the floor lining.

I prefer to seal my workshop as far as possible to prevent it from being re-charged with moisture-laden air.  My dehumidifier doesn’t run much of the time, unless I deliberately leave the door open.

[BazyleParticipant @bazyle]

You need a thing called a vapour barrier. This is a plastic sheet applied to the inside just inside the inner ply cladding to stop moist air moving into the insulation. It applies even if you are running a dehumidifier as some still gets away to spots it didn’t ought to be in. Each sheet is taped to the next to really stop any opportunity for air movement and thereby also makes it airtight in a gale.
You don’t need vents and ventilation – open the door in summer. In winter, at our age, there will be enough visits to the loo to let in some more air.
If you insist on a hole for air use 4in drain pipe, projecting at least an inch inside and out. You can get fully airtight caps to fit over the ends so you can seal it off both sides when you see sense.

[Robert Atkinson 2Participant @robertatkinson2]

Just my thoughts.This is an INSIDE enclosure so:

You don’t need vapour barrier in the walls.

Floor needs sealing. A liquid sealing compound under your flooring should be enough.

The outer wall should only need 9mm OSB not 11mm. If need be a tempary diagaonal on the inside will keep it rigid while errecting.

Put at least one run of noggins (horizontal connecting pieces between uprights) With a bit of planning these can be at the height where you might put shelves or similar later. mark positions or keep a drawing of locations.

Polystyrene foam sheet is OK if it is fully enclosed under ply or OSB. By the time th fire burns through that the PS will be the least of your worries. Where it hould not be used is in an uncovered overhead location. There it will catch fiare and drip molten flaming plastic on you.

A small closable vent is a good idea. When running the machines you will not need any additional heating. It may even get too hot in there.

Robert.

[Bo’sunParticipant @bosun58570]

I have my workshop in a double brick built garage with no insulation.  A desiccant dehumidifier, draft exclusion around the doors, and keeping the door(s) closed in the cold weather seems to do the trick.  An occasional light oiling with something like 3 in 1 also seems to help, and is easily wiped off.  The waxy type rust inhibitors are OK for long term storage but can be a nuisance to remove, especially on woodworking tools.

[Pete RimmerParticipant @peterimmer30576]

I’m just doing my new 40m2 workshop which is timber-built (essentially two large log-cabin style garages end to end with the gap filled in between). I’ve put 50mm enertherm sheets cut close between the rafters and lined the walls with 50mm knauf acoustic insulation between CLS batts with 18mm pre-painted OSB timber on the inside. This has allowed me to get rid of all the surface-mount plastic sockets the previous owner fitted and install flush-fitted metal sockets on the walls.

I’m not yet finished and the difference is already noticeable. My last workshop was built entirely from insulated metalclad panels and I expect this one will be as good if not better.

 

[Mick BaileyParticipant @mickbailey28509]

My stone- built workshop has a concrete floor with DPM and the main areas overlaid with hardboard. This has proven to be durable and more comfortable to stand on. The building is draughty and cold, but despite the stone walls there’s only significant condensation on a few days when the temperature suddenly rises after a cold damp spell.

My main heating is from a wood burning stove, though I have to plan for a rather long session to make it worthwhile to light as the roof is 15′ high. Usually I work for as long as I can in the cold doing model engineering, then retreat indoors for a few hours of firmware development for my other interest in electronic music.

I was intending to line and insulate the walls, but 4 years ago my neighbour, who has a similar workshop, battened out the walls and screwed on thick marine ply with insulation in the cavity. He’s a wood worker and made a superb job of accurately fitting the sheets and ensuring everything was plumb. After an unrelated visit by building control he received a notice to remove all of the plywood and replace it with plasterboard, which he had to comply with as they considered it a fire risk.

His workshop is detached, but about 10 feet from the main house.

 

 

 

 

[not done it yetParticipant @notdoneityet]

My workshop was originally less than 2.4m wide at the end of a 3.6m wide sectional concrete garage.  The concrete panels were substantially filled with cavity wall insulation batts.  I then covered that with 150mm of rock-wool and erected a frame from old (scrapped) up-and-over garage doors.  These have since been insulated further with another 25mm of celotex, or similar.  The ceiling currently has about 250mm of insultion

A couple of extensions to the workshop have been made with 100mm insulation sheets, and lined with ply sheets.  No windows, and ventilation is via the steel door (also with at least 100mm insulation).  Easily warmed in winter and cool in summer (unless the door is left open!).

Dehumidified (and warmed) by small Meaco desiccant machine.  Currently running at about 750W for two hours each night, costing about 14p/day.  Not a bit of condensation, or rusting, so worth every penny of the running costs.

[Nigel McBurney 1Participant @nigelmcburney1]

I agree that a timber shed within a garage is a good idea,  from 30 years experience with a workshop a rural environment,I would advise the following. glass fibre insulation its cheap relatively fire proof, mice and other vermin like burrowing into kingpin type insulation, and keep all wiring visible on the surface again mice like chewing pvc, Flooring to avoid any damp rising from plain concrete floors, my concrete floor was laid on plastic sheeting over a thick rubble base, then when the concrete had dried out, I placed a sheet of building grade polythene on the floor then laid two layers of 18mm chip board  to make a warm semi insulated floor, it was standard B&Q chip board not flooring grade, this will support any machine a modeller will have my case it was a   long bed Colchester Master and a 1 1/2 ton Elliot turret mill plus a Myford and a floor standing drill, the chipboard supported these machines easily and did not deform or put the machines out of alignment.I lined the shed with 12mm ply and only used 50 mm insulation in the walls and 100mm in the roof. The door opens into my outer workshop and is about 10 feet from the outer doors I am well into retirement I do not spend that much time in the workshop but I do not suffer from rust or condenthin ply lining, does get condensation and the power hacksaw and vices do get damp but they are covered in oil, and it does not matter. The one out side wall of the inner workshop is tongue and groove and to keep the weather out I placed a skin of thick polythene and this does work without causing any problems. Permeable membranes are perhaps ok in theory but they do deteriorate in time and cause leeks from wind blown rain. My wife’s stables are commercially bought and are clad in shiplap planks with a permeable membrane on the inside, in the section where hay is stored only the bottom half of the walls are ply clad and the membrane in the top is exposed on the inside, we live in an exposed position and rain does get blown into some of the joints and the membrane started coming apart only after a few yearsand now hangs in shreds utterly useless, Regarding the ply workshop wall lining I would use an 18 mm shuttering ply as it is better for supporting shelves I have found 12mm too thin.

[Chris CrewParticipant @chriscrew66644]

To prevent condensation you need to stabilise the temperature as much as possible. I keep an old convector heater under the bench switched to its lowest possible setting on 24/7/365. It obviously costs but is not consuming power when the ambient temperature rises. My workshop is a precast concrete garage with a ‘site office ‘ front built into the door aperture and only the roof is insulated. I have very few visits from the rust fairy. 

[John McCullaParticipant @johnmcculla]

And we’re underway!

I have all the sides built, using 3×1.5 timber. The floor will be 18mm OSB, resting on 2x2s, resting on the concrete floor. Planning to clad the outside for now, then insulate as I can pick up bits on Gumtree here and there.

[Fowlers FuryParticipant @fowlersfury]

I’m sure you’ll be aware that when working, the biggest source of water vapour within your workspace will be you. We humans exhale typically air at 35°C and 95% RH. The average human exhales 0.35 L/day of water in moderate activity. The amount varies with air temperature, relative humidity, and level of activity, so the range is about 0.3 L to 0.45 L per day. That exhaled water will condense if ambient conditions are around 12C and an RH of 80%.
I’ve found that starting a combined (electric) heater & dehumidifier about 30 mins before starting work and during the time “at the bench” does keep surface rust off ferrous surfaces. (Also, it provides large volumes of distilled water for the loco’s boiler and the boss’s steam iron). However the sound advice offered above about insulation is clearly important. For the concrete floor in my workshop/garage I purchased those interlocking heavy duty foam rubber tiles (about 1 sq m each). They are rot-proof and easy on – & warm – for the feet!

[John McCullaParticipant @johnmcculla]

Yes, I have a small dessicant dehumidifier which should provide a small amount of heat as well as drying the air, so I’ll plan to run that whenever I’m in the workspace, and hopefully that will keep everything rust free!

[John McCulla]

On John McCulla Said:

Yes, I have a small dessicant dehumidifier which should provide a small amount of heat as well as drying the air, so I’ll plan to run that whenever I’m in the workspace, and hopefully that will keep everything rust free!

John, if you haven’t already done it, and your dehumidifier has the facility, consider a permanent drain.  I was surprised how much water my dehumidifier collected.  And if the drain hose goes outside, don’t forget to protect it from freezing.

[not done it yetParticipant @notdoneityet]

I run my meaco 8ddl for two hours each night.  It was consuming 1.5kWh in the colder weather but presently only 0.75kWh for those two hours (since before Christmas).

1.5kWh would cost me about 40p/day at the energy capped rate?  Nearly three quid a week.

At night, on a cheap rate electricity tariff,  that 1.5kWh now costs me less than 15p.  Less than a quid/week!  Worth every penny to completely avoid condensation/rusting.

That £2/week, over the cool season, soon paid for the insulation in, and around, my workshop.  Some of that insulation has been there over 30 years.  Go figure the cost savings provided by the insulation over that time.  I’ve only ever paid full price for 2 (or maybe 3) 25mm sheets of Kingspan.  The rest has been bought at very economical cost from a variety of sources.

[John McCullaParticipant @johnmcculla]

Bo’sun – Yes, I have been using the permanent drain feature. Definitely necessary as when collecting in the built in tank it fills up, as you say, surprisingly quickly, and then turns itself off. I’ll have to give some thought to the mounting of the dehumidifier and the drain in its new home now.

 

not done it yet – Good to know. I’m hoping to get away with only running mine every so often (plus when I’m in there) if the shed is very well sealed, but it will require some experimentation once the building is built to see what’s needed. Yes, I’m hoping to avoid paying full price for any insulation too!

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I built my garage with a steel frame and steel sheeting, which was all recycled scrap steel from my employment back then, but I was with a very low budget, so buying a vapour barrier was out of the question, however, the company I worked for, had material delivered in single use two ton bulk bags, and these had to be skipped, as they were non-returnable, so they had no problem for me to take as many as I wanted. These had the tops and bottoms cut off , and then cut along a joining seam and opened out into large sheets, they were then sandwiched between the steel frame and the outside steel sheeting, which has proved very effective to prevent condensation forming on the sides and the roof, which can just be seen at the front end where the last sheets need to be put in place, in the photo below.

Regards Nick.

[Pete RimmerParticipant @peterimmer30576]

I have just about finished mine now. I used CLS battens at half board width and insulated with knauf acoustic roll which comes pre-cut at 600mm centres. On top of this I put edge-sealed and painted 18mm OSB3 which produces a very good base for sockets and wall fixings then cut the socket holes into the walls to fit flush sockets in place of the surface-mounted ones that were there previously. It wasn’t cheap and was a lot of work but so far I have not had a speck of condensation and the light coloured paint on the boards means I have been able to swap the 13 twin fluorescents for 9 LED panel lights giving a much brighter workspace and has also reduced the energy consumption of running the LED lights to about 20% of running the tubes.

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