Insulated Shipping Container Help

[jimmy_s]

You really want to try and ventilate between the insulation layer and the steel container as its where the moisture will migrate to during cold weather one way or another. The pressure difference between the water vapour in the warmer air causes the water vapour to migrate to the colder surface (Daltons law of partial pressures) If you can ventilate the air gap it should help as the vapour willl be dispersed to atmosphere also some vent into the container itself will help. Its a form of interstitial condensation.

Amazing how it builds up, in larger cold stores they have to heat the floors otherwise the water vapour migrates to the coldest part - normally the centre of the floor and freezes, eventually bursting the floor. Caused by partial pressure differences between the water vapour in the airstreams.

God I'm getting sad. Back to fixing the lawnmower!

 

[jcassidy]

I feel for you. That looks like a lot of work. Luckily condensation is easily sorted. It's just water vapour vs, cold.

I don't see a vapour barrier on the insulation boards? I'd expect to see OSB, vapour barrier, insulation, air gap, outer wall.

 

[PJBuzz]

This lady has looked at some of the issues around re-purposing of containers, (shame some have given her a tough time about it )

She also mentions an air gap between insulation and outer metal skin and water gathering at bottom of walls I recall.

I always imagined if I had one I'd have a single pitch roof for shade from the sun, (I was in a caravan once and it rained, so noisy !) so a pitch when it rains, that would have hinged access for storage.

Now I think about it , maybe that would allow for puncturing the top surface allowing for ventilation opportunities in the horizontal, even the keeping of an AC unit or air compressor and other noisy items dry and out of the way but yet semi protected from casual theft(?)

Well good luck

Regards,
Dave


PS Heres her part two ;

To be honest, after doing the build I reckon I would have been far better served building a shed, or pushing a bit harder to use an old dog kennel building they have on the land.

Live and learn though, and they have another container on the land they're considering doing

 

[PJBuzz]

I feel for you. That looks like a lot of work. Luckily condensation is easily sorted. It's just water vapour vs, cold.

I don't see a vapour barrier on the insulation boards? I'd expect to see OSB, vapour barrier, insulation, air gap, outer wall.

No there isnt a vapour barrier as such, I have basically used the aluminium tape to try and seal everything up around all the insulation boards as well as I can, but I don't see how a vapour barrier would work here anyway, as the cables would all have to poke through it. I could put a piece of plastic up, but Im not toally convinced I would ever get a better seal, and would actually possibly end up risking any condesation that does occur pooling up inside the plastic and rotting the wood in a way that I would never know. At least without the plastic it will drip through the edges of the wood and I can address the problem.

It would also mean rippng EVERYTHING out and starting again, which I would prefer to avoid if possible.

 

[Fitzroy]

I do think you’ve nailed the issue as being condensation, ventilation is likely the first thing to try.

 

[jcassidy]

Condensation only occurs when moisture laden air comes into contact with a cold surface. The presence of a vapour barrier on the warm side of the insulation prevents this and the usual ventilation present in any room will equalise the warm moist air with the cold air outside. Unless you want to suffocate.

Anyway, the lack of a vapour barrier is the issue. You will have to resolve it with mechanical ventilation as suggested in other posts, but critically this must be between the insulation and the outer shell, to suck all that moisture away. The fact that you have ensured an air gap between the insulation and the shell will enable this solution. I use an extractor fan powered off the light switch with a timer, which I set to 20 minutes, so the fan runs when the light is switch on and for 20 minutes after the light is turned off. This efficiently removes all the moist air from the void and I don't have condensation issues. I got it off screwfix.

Adding extra ventilation to the warm space will increase your heating costs. There are some cool DIY heat exchanger designs about which you might look at. I would look at ventilating the unheated void space before looking at more ventilation for the heated working space.
Hope this helps,
John C.

 

[Fitzroy]

Another thing is that a little water goes a long way. When we had our first child my wife was anxious that he was getting no sustenance as he was throwing up all the milk he drank. I resorted to throwing 50ml of water on the floor to show how much mess only a little liquid makes.

An average person will loose 500ml-1000ml per day through respiration/perspiration.

Fitz.

 

[PJBuzz]

Anyway, the lack of a vapour barrier is the issue. You will have to resolve it with mechanical ventilation as suggested in other posts, but critically this must be between the insulation and the outer shell, to suck all that moisture away. The fact that you have ensured an air gap between the insulation and the shell will enable this solution. I use an extractor fan powered off the light switch with a timer, which I set to 20 minutes, so the fan runs when the light is switch on and for 20 minutes after the light is turned off. This efficiently removes all the moist air from the void and I don't have condensation issues. I got it off screwfix.

What I'm trying to get across though, is that I don't actually think that it would be possible for me to get a better vapour barrier than what I have already done. The vapour cant get through the aluminium tape which covers the timber, and it cant get through the insulation board which is also covered in an aluminium layer... the whole box is covered in that.
The only places it can get through are cable gaps that would also be present if I was to install an additional product, or the slightest gap here and there from installation damage, that is also quite likely with a plastic coating.

I'm not trying to be argumentative, and perhaps I'm missing something, but I can't visualise how I would install a layer between the OSB and the insulation that would make a more vapour tight seal than the one that exists.

 

[pcb1962]

I actually found a site selling container vents at a decent price, so I have ordered 8 of the small ones (don't know if I will use all 8) and one large one. They look reletively straight forward to fit.

If the vents don't come with a mesh backing then you might want to sandwich some of this between the vent and the container to keep insects out.

 

[jcassidy]

I checked the ecotherm installation guides (because I'm awake at 4am house training a puppy) and it does suggest that a VPM is only required when installing between battens, whereas you have installed over battens.

 

[harvestbarn]

Have a read of this article The ultimate guide to shipping container condensation treatments

When your dehumidifier arrives run it 24hrs a day and try turning off your heating. The less temperature difference the lower the condensation. Fit a min max thermometer with humidity reading so you can monitor what is going on. If you have removed the moisture in the air rust on your gear is less likly, give what you can a coat of protective wax.

Things may not be as bad as you think, good luck.

 

[okeydokey]

Okeydokey

Its the other way round. The fan gets the air from the vented loft space, filters it and pushes it into the house.
In effect it dilutes the stale moist air in the house by constantly forcing new air in. So the concentration of moisture is reduced.

They do a different version for flats which use a hole drilled to the outside, which would work for shipping containers.

Today there was no moisture on my windows, previously there would have been streaming moisture and maybe a small puddle on the window cill at these temps ( below zero outside).

Ollie

Aha
Thanks

 

[PJBuzz]

I checked the ecotherm installation guides (because I'm awake at 4am house training a puppy) and it does suggest that a VPM is only required when installing between battens, whereas you have installed over battens.

Maybe I don't understand the terminology, but pretty sure I have it between the battens, as in they sit inside the wooden structure, not on top or behind it.

 

[PJBuzz]

Whilst I will be installing extra air vents, possibly a second roof to reduce ice build up, I have also been looking at fans to circulate the void air... but I'm not exactly sure what I need to be looking for here.

Although there is an airgap between the frame and the outer shell, it's only a few CM so I'm not sure how I would have a fan in there, behind the inside structure... I'm also not sure if there is any way of making that up to "code".

Also the dehumidifier arrived, so that's going in.

 

[Bod]

In the steel narrowboat world, it is accepted to prevent condensation on the inner surface of the steel shell, the insulation must be in hard contact with the metal, so no gaps are able to condensate.
The most effective way of doing this is to have the internal surface "Spray Foamed" to a depth of at least 50mm.
In a shipping container, all ready lined out, I can only think to put expanding foam into each space.

Bod

 

[harvestbarn]

We had our container Spray Foamed onto the steel and it has worked out well. It could be done drilling holes just like a cavity wall as a last resort but you look to have done a tidy job and I suspect it will settle down

 

[Jameshow]

How about a false roof above the container?

4x1 tapered timbers either apex or pent roofed with insulation 18mm ply and felt in top might reduce the temp difference.

Cheers James

 

[Dave Moore]

Hi,
I think you would need an airspace between the metal and the wood to allow the condensation to run to the bottom of the wall. I suggest you look at the website of Cedral where you can download free installation instructions. Although you aren’t looking to clad the outside it might give you some ideas that is required for ventilation. Incidentally because you have the metal shell you will need a way to get rid of the moisture which would require a way of draining it.
Regards,
Dave

 

[NormanB]

I am probably a heretic but I think the general advice here is to have positive ventilation between the insulation and the interior steel wall, I think this is exactly the worst thing to do. That advice apply to wooden buildings insulated lofts etc but that is so timber is ventilated to keep it in good condition.

My view ( and I am not an expert in this at all) is to exclude any air behind the insulation and bond all of your insulation to the inner steel surface, no gaps, no voids whatsoever. Then ensure the surface of the insulation facing the workshop is totally impermeable. The aim is to have no air (moisture) migration to the insulation/steel interface. The result should then be the only surface that can precipitate condensation is the inside surface of the insulation which standard ventilation, (opening windows, dedicated ventilation ports, open doors) should be able to mitigate.

 

[glenfield2]

I am probably a heretic but I think the general advice here is to have positive ventilation between the insulation and the interior steel wall, I think this is exactly the worst thing to do. That advice apply to wooden buildings insulated lofts etc but that is so timber is ventilated to keep it in good condition.

My view ( and I am not an expert in this at all) is to exclude any air behind the insulation and bond all of your insulation to the inner steel surface, no gaps, no voids whatsoever. Then ensure the surface of the insulation facing the workshop is totally impermeable. The aim is to have no air (moisture) migration to the insulation/steel interface. The result should then be the only surface that can precipitate condensation is the inside surface of the insulation which standard ventilation, (opening windows, dedicated ventilation ports, open doors) should be able to mitigate.

Based on steel boat experience, I’d agree with you - that’s why most use Sprayfoam straight onto the steel these days. I’ve just stripped out an old boat with very well applied polystyrene boards and it was remarkable how much damp and rust had still got behind them.
if the only evidence of damp is dripping from the roof then I think I would drop the boarding and bond a layer of celotex stuff direct to the steel, sealing all gaps with the foil tape and covering any cold bridges.
I’d also have a couple of roof vents (boats use mushroom vents) but away from anything that might get spoiled by drips blown in).