Sheds and condensation avoidence thereof

Enough background heat to keep the temperature above the dew point basically.

In my workshop I use a wall mounted fan heater run from an external stat, set at about 6 or 7 degrees.

I would have thought that you would not have a problem without a source of humiIdity like steam from cooking, drying clothes, people living in it or rising damp. If you do, maybe because of warm days and cold nights (as boats do) then a dehumidifier should keep it at bay.

Insulate and use electric heating, which has a drying effect. My latest shed has 100mm insulation in the roof, 50mm under the floor and 25mm on the walls, which seems quite adequate in all weathers.

Colin Bignell

Basically dehumidifier or heat. Dehumidifier is far cheaper to run.

NT

The problem is the faster temperature rises that cause items having a large (undefined) thermal mass to lag far enough behind the rising temperature to fall below the dew point.

If your shed gets down to say 2 degC overnight with 50 percent humidity, then if the morning sunshine causes a rapid rise in temperature to say 10 degC, it's a racing cert that large items will only have reached the dew point of 4 degC when the shed thermometer reads rather higher than this.

As moisture settles out from the air, every surface including internal ones that have a pathway to air will suffer condensation, with all the problems that can cause.

Heating such a shed to a temperature having a high probability of avoiding the dew-point problem (10 degC might be such a figure) would cost a fortune unless extremely well insulated. Dehumidifiers could be a way to go, but you'd need one that works down close to 0 deg C and they are expensive too.

Some combination of insulation, humidity control, and emergency electric heating would, if you kept your eye on each day's overnight weather forecast, avoid the most of the problems, but finding where the balance should be struck between these three is going to be interesting.

TF

Unfortunately dehumidifiers don't work at low temperatures. Condensation is a well known problem in sheds. Basically as the weather warms up, the air holds more water. This condenses on anything that's colder, especially at night as the air temp drops anyway. Large lumps of metal are particularly suseptible, smaller ones less so. My lathe always suffers as it's nearly a ton of cast iron. Stationary engine enthusiasts are always moaning about condensation. They spray everything with various oils to protect the metal. That may not be an option for you. I'm assuming your models are relatively small. The only answer is to heat, and possibly duhumidify the shed. The trouble is that's expensive.

John

My shed, 14"x 8", complete with model railway. Outer skin horizontal timber shiplap boards, underneath is a layer of breather roofing underlay all the way round and including the roof and floor. Roof & floor is constructed of t&g boards. The roof is covered with top quality mineral felt, under the roofing boards in between is 50mm insulation boards fitted tight up to the underlay. The floor as a layer of breather underlay covered with 12mm insulation covered with clip fit boards. The inside walls have 50mm insulation fitted tight up to the layer of breather underlay covered with 12mm sheet ply board. In the winter I have and electric heater with a thermostat sitting, this is set just to keep the chill off and try to keep any condensation at bay. I=92ve had no problems apart from the heat in the summer, it gets a little to warm and a few spiders.

Chris Wilson wrote in news:Xns9E7395626C796ulmbritwarcouk@69.16.176.253:

Thank you all very much for the tips, ideas and "heads up". If I haven't replied personally it doesn't mean that I haven't read your post, let alone valued the advice contained within for I have.

Kipper at sea wrote in news:77b2da60-93e5-400b- snipped-for-privacy@o21g2000prn.googlegroups.com:

Cool, so it's skin, underlay then insulation in that order. Have you put an internal skin on the walls/roof or have you left the underlay exposed?

John wrote in news:32fc22da-4c2f-4dd4-86ec- snipped-for-privacy@d1g2000pra.googlegroups.com:

Presumably it acts a little like a "precipitation sink" a la "heat sink". I wonder if it'd be worth putting in a big old cast iron radiator on a sacrificial basis to collect the worst of any condensation that appears.

Chill it with a small heat pump and you have - a dehumidifier!

Fit an (Inverter) heat pump air conditioner. Cheaper to run than an electric heater and has a built in dehumidifier function as well.

Incorrect, but I did forget to mention that some dont. For winter use you'll need an absorption unit, not a compressor type.

NT

I visited a few timber shed makers and one in partially had the idea of covering the ends & sides of the timber frame with tar paper on the out side then fixing the ship lap boards on to the timber frame. So I decided to use this company but supplied them with a roll of roof shield breather underlay. They covered all sides, ends and the roof. after they had erected the shed I filled all the gaps between the frame on the inside with insulation and ply boarded over.I was going to use plaster board for the inside but decide it would make it more secure to use 12mm ply. The surplus underlay I covered the floor with and then covered with insulation and clip flooring. The roof on the inside I cut sheets of insulation and tight fitted them in the frame of the inside of the roof up to the underlay and held it in with nails driven into the frame sides not through the insulation. One thing I did do was to raise the concrete base above ground level and make the base small enough to fit inside the ship lap board so the rain would not run under the floor supports.

Don=92t use tin roofing of fibre cement sheets they are known for condensation. Stick to a top quality heavy duty bitumen granule felt fix to t&g boards.

I'm going to throw something ad hoc in here:

My old man kept all his steel tools in a big wooden cheast of drawers in a mouldy damp garage with a non DPC concrete floor.

Wind howled through both door frames and the window was dodey, though there were no liquid water leaks.

The tools, including planes stayed in near mint condition.

The chest was heavy (2' x 4' x 3-4' high and 3/4" thick wood. The drawers were close fitting and the inside bare.

It was his theory that the wood acted as a buffer taking in free water in preference to it condensing out - also the wood did have some insulation value.

So perhaps a wooden cupboard for tools - real wood or thick ply, painted or varnished on the outside, bare inside and well sealed (close fitting or draught strip)...

Also, if using a small instrincally safe heater[1], or dessicant, they will go a lot further in a small sealed space...

I realise if the OP wants a trainset or large tools to be protected, this won;t work, but for all the small and power tools it could - and an excellent inscentive to put away :)

Though a sort of lid that comes down over the trains - even if it's just a board with a short curtain round it would help. Fit a tube heater underneath and it'll keep it all snug when not in use.

I have found this fascinating. I built myself a new workshop 3 years ago which has both metal working and wood working lathes - both large and CI. There is also a circular saw, band saw and large vertical drill. I live near Edinburgh. So I live in a cool, dampish area and have a lot of metalwork on which moisture could condense if it wished.

I do not have any problems, and I haven't made any specific provision against condensation either that I know of.

The shed is an extension to a garage and being on a sloping site its concrete floor is raised above ground level on 2 sides. There's a dpm in the concrete and rubber matting on the floor. Wooden frame, 2 windows, 2 doors, 3" timber framing with fibre glass insulation and weatherboard facing, no breathing layer under the weatherboarding, but a dpm under the inner lining of OSB board to prevent condensation in the insulation. Roof is insulated, and covered with Onduline over OSB, plasterboard ceilng. Basic electric fan heater with internal thermostat that is turned to minimum every night.

I was interested in the story about storing the tools in a wooden chest and wonder if the relative air tightness of my workshop and the presence of quite a lot of wood and shavings act as an absorber of the moisture and it doesn't get a chance to settle out on cold surfaces.

I did wonder about condensation when the shed was being built and a humiditistat controlled extractor fan was installed, but found to be unnecessary and has remained switched off.

I'm sorry if my story flies in the face of everyone else and creates confusion. One possible factor in thinking about it, is that only in error do I allow the workshop to get much above 10 or 12 C in winter, usually finding that a padded boiler suit, etc. is adequate even for fine work.

Rob

innews:Xns9E7395626C796ulmbritwarcouk@69.16.176.253:

I have this problem in my workshop and heating it is a no go. The best answer I found was to cover those machines prone to rusting. Table saw, band saw, spindle moulder and planer thicknesser all have their own 4mm ply cover. Little trouble to put on and remove. Smaller machines have a canvas cover and all else goes into drawers. I uses Renaissance wax on the hand tools and machine wax on the larger machinery though it isn't really necessary as the ply does the job on it's own.

Possible with a model railway you could provide some sort of a fabric cover ?

Paul Mc Cann