Garage / damp / cold

[David]

+1 for electric fan heater and good advice on paraffin / propane heaters. Many years ago in the impoverished 1970s we had a paraffin heater in our house and everything was permanently damp.

You should have tried living in a caravan with one, it was like a freezing cold swamp.

I had freinds on a boat in Holland ...they had insulated, but not closed off a lot of it. They used parafin heaters for a couple of winters....damp? More like drizzle. gas fires are the same. I have one in my shed, but also a wood burner. I very rarely use the gas heater....it wouldnt be in there except that it was a freebie.

[formula400]

cold in there today, but no condensation on windows. ill see how it is and look at a tube heater (ill be able to take that when we move so may come in handy for the next garage as well)

[DEADPOOL]

The issue with condensation is fairly simple and understanding the mechanism might help you find the best compromise.

The simple version is that condensation occurs when air of any temperature meets a much colder surface which is a good conductor of heat. As the air meets a much colder surface it is chilled below its dew point so that whatever moisture it was able to hold is dumped out of its vapour phase into liquid.

A typical solution is to hermetically seal your shed so that everything is maintained at "the same" temperature. Problems arise generally for two reasons.

The first obvious one is if you have a metal roof, that chills down much more quickly than the volume of air sealed inside the shed. Compounded by the fact that any warm air or breath rises to the ceiling, chills, dumps its water and now being colder, pushes warmer air from below creating a circulating current.

The second less obvious one we will all be facing right now is that our sheds have all been cooled down, everything inside is stone cold, then the blasted weather gets all warm again and the moment you open a door, all that warm moisture laden air is going to hit the lathe, milling machine, spanners, bikes, windows...

You can keep the inside the same temperature as the outside which will cure problem #1 but then you're working in a freezing cold shed. It won't help at all with a sudden warm spell because the air temperature outside will increase much more quickly than the big iron inside your shed. You can leave the windows open then heat the shed once you're in there so long as your heater isn't creating moist air (like a paraffin stove/space heater) but that's a pain in the arse.

Best bet is to hermetically seal the shed (block off as much airflow as possible), then insulate the roof to prevent warm air from touching the cold inner. There are (at least) two main options. Glue an insulating layer directly to the underside of the ceiling so that no air can get to it. That is quite tricky so option #2 is to have an insulating layer quite well sealed, then a small gap between the bottom of the "cold roof" and allow that gap to be ventilated to the outside air.

With a well insulated shed you still have to be wary of opening the doors when it's stone cold inside and warm outside. If you do that on a warm day after a cold spell, everything gets drenched.

The very best solution is a hermetically sealed shed with a ventilated (cold) roof and a small anti frost heater permanently keeping the temperature above the dew point which in the UK winter averages around 5-10 degrees C. In this warm spell, the dew point will be much higher...

[formula400]

I am pretty sure its not a metal roof, the is a slight gap between the roof and the ceiling, the ceiling is wooden,

I think trying to seal up the garage might be the best option and getting a little antitrust heater in there, would it need to run 24hrs??? what do they cost to run 24hrs or is that unnecessary

[formula400]

since removing the draft brush from the bottoms of the door and leaving the windows slight open there has been no condensation inside on the sky light, now not sure if its working are that its slightly warmer.

[Le_Fromage_Grande]

I am pretty sure its not a metal roof, the is a slight gap between the roof and the ceiling, the ceiling is wooden,

I think trying to seal up the garage might be the best option and getting a little antitrust heater in there, would it need to run 24hrs??? what do they cost to run 24hrs or is that unnecessary

Don't seal it up, it will make it worse, ventilation is the answer.

Generally what happens is that during the day when it's warm water is sucked up out of the floor into the atmosphere of your garage (tin shed in my case) then when it cools later in the day that moisture condenses on the coldest surface, usually the roof followed by the walls. Ventilation gets rid of the moisture, insulation stops the roof getting as cold.

I tried insulating my tin shed with cardboard and it got rid of a lot of the condensation, until the cardboard got soggy and fell apart, I'm going to do it properly with this foam sheets when I can be arsed.

[DEADPOOL]

I am pretty sure its not a metal roof, the is a slight gap between the roof and the ceiling, the ceiling is wooden,

I think trying to seal up the garage might be the best option and getting a little antitrust heater in there, would it need to run 24hrs??? what do they cost to run 24hrs or is that unnecessary

It would need to maintain a temperature above the dew point but you might be able to achieve that with 0.5kW heater or a tiny fan heater. You might get away with running it off a timer or having a simple thermostat. The precise wattage will depend on how well insulated your shed is. All the heater needs to do is keep the chill off but (to be slightly absurd for a moment) if you had 100% insulation in your shed, a small candle would eventually heat the entire space to red hot.

So find a mid point, decent insulation, no draughts and a smallish heater will do.

You could look at solar powered storage heaters etc. remembering it's only for a period of the day for part of the year. Costs should not be prohibitive. The nice thing about having a well insulated shed it it will be a pleasant space to work in. What is that worth?

Don't seal it up, it will make it worse, ventilation is the answer.

Generally what happens is that during the day when it's warm water is sucked up out of the floor into the atmosphere of your garage (tin shed in my case) then when it cools later in the day that moisture condenses on the coldest surface, usually the roof followed by the walls. Ventilation gets rid of the moisture, insulation stops the roof getting as cold.

I tried insulating my tin shed with cardboard and it got rid of a lot of the condensation, until the cardboard got soggy and fell apart, I'm going to do it properly with this foam sheets when I can be arsed.

You make a number of assumptions. Sucking moisture out of the floor is one of them. First time I've heard that! The floor will typically be at a similar temperature to the other surfaces in the shed so if water can condense onto the roof/walls, why wouldn't it stay liquid in the floor? What mechanism would cause water to evaporate into a vapour and charge the air with moisture if conditions are ripe for condensation?

Not saying it's not possible and a damp floor will create a damp environment but the primary mechanism is moisture already in the air due to prevailing atmospheric conditions.

The roof does not have to be the coldest surface but merely where the temperature differential is highest remembering there is a temperature gradient in the volume of air. The roof does generally chill first because it is the most exposed plus walls are often more insulated surfaces and do not conduct heat away from air so well as a metal roof.

Ventilation does not "get rid of the water", it cools the shed so that there is no temperature differential. There is no warmer air in the shed to meet a colder surface. All you are doing by ventilating the space is keeping the interior at around the same temperature as the outside air.

I think I'll just pass on the cardboard insulation idea with no comment. See above for how to make contact insulation work but having a "cold roof" design is by far the most common practice (gap and vented). I put cold roof in inverted commas because that is the technical term which Google will recognise if you don't believe me.

[demographic]

A cold roof is best done by insulating the roof, vapour barrier to stop moisture from getting into the insulation from the inside and ventilating the area above the insulation so when its warm enough the water vapour can escape through the ventilation.
Thats why soffit vents exist, and ridge venting.
Also damp concrete adding to the general moisture levels in the buildings are the main reason we put a DPM under concrete floors nowadays. Even some houses with raised timber floors get a DPM in the solum (the gap between the ground and the raised timber floor) and a concrete blinding to greatly lessen this. That DPM also lessens Radon in the buildings but thats a side issue.

[Doc]

You could fit an extracter fan with a humidistat. I'd be happier with that rather than leaving a window open/ajar.

[demographic]

This is more about houses and areas that are heated more often but most of us own a house so I reckon its worth watching so we have a bit more knowledge about how it works.

It also explains why downlights are often such a fucking disaster in kitchens and bathrooms.

[ZRX61]

Ventilate ...
I have a man shed - 4.5 m x 10 m. It's damp - most thing fabric pick up mild dew, tools go rusty etc.
I have a greenhouse heater under the tool chest now.
Garage - also single skinned etc - faces directly east/west - wind blows through the gaps in the door.
It's never damp -and the bikes like it in there much better ...

Those heating pads for terrariums work well. Remove bottom drawer, lay a ceramic tile in the bottom of the cabinet, put heating pad on it & drill a hole in the back of the cabinet to feed the power cord through.
Within a day the entire stack is toasty warm.