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.

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