Insulated Shipping Container Help

[PJBuzz]

Hi Everyone,

I've been browsing this site for a while, it's been an incredible resource for me whilst I have been trying to set up my own little workshop. I am still very new to the world of construction and DIY, my normal job is designing and commissioning broadcast systems... so I'm well outside my wheelhouse.

I also did find a similar thread to this, but rather than necro a thread from many years ago, I thought it made sense to keep this topic self contained as it's less of a "give me advice on how to approach this, and more of a "PLEASE HELP ME TO FIX THIS INSTEAD OF ME STARTING FROM SCRATCH" kind of problem. I don't want to push an old topic way outside it's original intention.

I have a 20ft shipping container that I and a friend framed out, added a personnel door and a window, then added 50mm "ecotherm" insulation boards between the frame (walls and ceiling), filled in any gaps with expanding foam, I added silver insulation tape across all the joins and gaps to try and seal the internal "box" in completely, I then installed OSB on top of that. The job I did with all that was definitely not up to the standard of a pro, but I figured I had done a good enough job that it would keep me warm and dry when working in there.

I came to the container today, to start assembling my CNC router... and I noticed dripping from the ceiling.

Obviously, there is a problem. Either a leak or condensation. After some investigation, I'm pretty sure it's condensation.... a lot of condensation.

Now I really, really don't want to rip everything out and start again, as this will basically kill the whole project. I simply can't afford to do something like that, so I need to do my best with what I have.

Hopefully you guys can help me solve this without ripping it all out. The places where, after some discussions and reading, I think I have gone wrong are:

1. Cold icy weather on the outside has resulted in ice on the roof of the container
2. I have had heaters running, so the "box" inside the container is warm
3. I stupidly sealed up the vents (pure ignorence on my part) that would have allowed airflow on the outside of the "box" - thinking I can grind these off and affix some normal air grilles to the side to allow the outside of the "box" to breathe.
4. I want to still be able to use the big double doors, so the "box doesnt have 4 walls. I just stuck some insulation on the door for now. Issue here is that around the edges of the open wall, I didn't seal them up to the top/sides of the container, so effectively it wasnt a complete "box", it was just 3 walls and a ceiling insulated, but the air could flow between.

Thanks in advance guys.

 

[Fitzroy]

The cold space behind your insulation needs venting. In most cases there is some degree of permeability of the outer skin of a construction, then the inner ‘box’ just needs to be less permeable to any water vapour. In this situation any moisture that gets through the inner box can escape at the same rate. In your case metal is totally impermeable and even if only tiny amounts of water vapour get past your box it will build up and eventually cause issues. Venting the air gap behind should have no impact on the thermal properties of your room as the insulation is all inside this boundary. The metal box is really just a weather screen, and physical structure to support your inner box.

Lots of ventilation, with guarding to prevent rain ingress, and mesh to prevent insects and vermin.

Re-reading your post, the detail between the doors and your box needs consideration, if it’s badly done you could get drafts once you open the vents. Great for limiting the condensation problem, not great for comfort and heating bills.

Fitz.

 

[PJBuzz]

The cold space behind your insulation needs venting. In most cases there is some degree of permeability of the outer skin of a construction, then the inner ‘box’ just needs to be less permeable to any water vapour. In this situation any moisture that gets through the inner box can escape at the same rate. In your case metal is totally impermeable and even if only tiny amounts of water vapour get past your box it will build up and eventually cause issues. Venting the air gap behind should have no impact on the thermal properties of your room as the insulation is all inside this boundary. The metal box is really just a weather screen, and physical structure to support your inner box.

Lots of ventilation, with guarding to prevent rain ingress, and mesh to prevent insects and vermin.

Re-reading your post, the detail between the doors and your box needs consideration, if it’s badly done you could get drafts once you open the vents. Great for limiting the condensation problem, not great for comfort and heating bills.

Fitz.

Thanks for the response mate. I should mention the mate that helped me is a professional joiner, and he does restorations for a living, so it's not two idiots... just one.
He didn't do all the insulation and OSB, that was purely done by me under a bit of instruction by him.

For clarification, the door and the window have a frame/cil of external ply so that it covers the threshold between the framework and also the corrugated metal in the container. This is then affixed to the internal wooden framework, then all gaps around the edge sealed up with expanding foam and/or a heavy duty building sealant. This is an area I'm very confident has been done to a level that wont let in any moisture or drafts.

It sounds like my research had taken me on the right track... so if I:

• Open up the vents I stupidly sealed, perhaps add a couple more.
• Go around some of the existing spaces where I have holes between the "box" and the air space and seal those up (im thinking of places where cables come through, as all of that is behind insulation... but nothing is actually wired to mains yet so it's totally safe) and add in some sealant around those to imporove the vapour barrier
• Seal up the ends of the wall and the ceiling near to the double doors, again, to improve the vapour barrier

Then the problem might be... resolved?

I don't know if this comes across in my posts, but currently I'm a broken man with this. It's been months of work and when all the water dripped from the ceiling, my heart utterly sank. A lot of the similar projects, people have taken a totally different approach to me.

 

[Woody2Shoes]

What kind of heater have you been using? How dry was the timber you used for the framing?

 

[PJBuzz]

What kind of heater have you been using? How dry was the timber you used for the framing?

I had a 500w oil filled heater at one end, and a 1KW convection at the other. Overnight I dropped the temps of them down to either 5c or 10c... i forget which.

Tonight everything is switched off.

IIRC it was typical and cheap CLS 38x63 straight from the local wood merchant. Don't think it was treated or anything like that. Bearing in mind when we started the framing, the weather was decent and there has been long gaps in this project when I actually had normal work, when my mate was unavailable, or when we were waiting for materials

The wood was all stored in the container between phases of the project, so minimal chance the wood soaked up a lot of moisture. It's only since the heaters have been running that I have ever noticed any moisture build up in there. It was dry as a bone when we started and throughout the build process.

It's only fairly recently that I have been running a heater, as I was waiting for a spark to come and sort out the armoured cable. As that's been pushed back I have a less permanent solution currently, but it is sealed up and safe.

 

[harvestbarn]

I would put a dehumidifier in your box working 24 hours a day and reduce the heating temperature to about 12 degC they are cheap to run. Turn the heating up when you are in there working. We run a CNC and SLS printers in a similar way the weather has been very humid recently.

 

[PJBuzz]

I would put a dehumidifier in your box working 24 hours a day and reduce the heating temperature to about 12 degC they are cheap to run. Turn the heating up when you are in there working. We run a CNC and SLS printers in a similar way the weather has been very humid recently.

Thanks mate.

I have ordered a relatively small one (12l) so I will be doing exactly that!

need to figure out which vents i can actually use as the shape of the metal obviously makes it a bit tricky for flat mounted ones. Proper container ones are... expensive.

 

[Ollie78]

As said ventelation is probably needed. I have a little recent experience with this, we have been struggling with condensation in our house.
Last year we bought a dehumidifier which helped some but not enough.

After much research I decided to try Positive input ventilation or PIV. This involves fiting a fan unit in the loft with a vent into the upstairs ceiling, these are specifically designed for the purpose are low energy and very quiet and have filters.
The idea is that the amount of moisture in the air of the house ( or shipping container I assume ) just becomes too high then it rushes to condense on anything cold enough. If you constantly change the air then the amount of moisture per m2 of air is significantly reduced and so there is not enough to condense. Effectively removing the "cloud" from the house.

I was a bit sceptical but it does seem to be working and not making it cold or anything, you can feel the air movement if you stand right under it but not much.

Air movement is certainly the answer in one way or aanother.

Ollie

 

[okeydokey]

Hi Ollie
Seems interesting would you explain a little more please.
Have I got this right?
The fan in the attic draws air, possibly warm and with some moisture into the attic space? If so does this make the attic a little moisture laden so that moisture can condense onto the roof timbers/sarking/tiles or what have you?

 

[Ollie78]

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

 

[Fitzroy]

Sorry to hear you’re a broken man, I know how frustrating it can be when lots of hard work feels like it’s been wasted. Keep your chin up though and you’ll get it sorted. As per advice above air movement, moisture management, and dehumidification are the way to go. It may take some time to dry out but you’ll get it there.

Eliminating other items on your list is also important, you mention ice buildup on top of the container, how confident are you of the integrity of the container roof? Ice can reveal issues not seen during rain as it can melt over long time periods and it’s like having rain all day for a long period. Looking at pictures of shipping containers it seems doubtful this is your issue, unless you have physical holes as a leak on the side of the roof panel would likely run down the internal wall.

Fitz.

 

[Fitzroy]

Did you take any pictures during the fit out? May help the grey matter be clear on what you’ve done.

Another way to confirm your suspicions is to cut an inspection area out in the ceiling and take a look. If you do this don’t be surprised not to find precisely what you were after. I had a leaky bathroom ceiling for a while and I cut a hole only to eventually find the leak was 2m away, the water was just pooling and dripping where it found the path of least resistance. It should however let you see if the container roof is wet with condensation.

Thinking about the above posts a form of positive airflow would be a good option. Someone on here installed computer fans in their underfloor void to guarantee airflow. Opening a vent on one side and installing a fan at another location to force air through the cavity could be really successful. I’d blow into the cavity, rather than suck out from it. You want a positive pressure in there so any air leaks into your box, rather than a negative pressure and any air leaks pulling moist air out of your box.

Fitz.

 

[Jameshow]

How about some mushroom vents as seen on caravans

Or a swirl vent you see spinning on top of vans. They create thier own airflow.

Or another idea is a cowling made from 100mm 90° pipe bend fixed in a nw direction as the prevailing winds come from the SW.

Has the window at the front got trickle vents if not get some and fit.

Cheers James

 

[PJBuzz]

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.

That all makes sense, but it's possibly overkill. I think, for the moment at least, I'm going to vent the air gap with a load of little vents, and see how I get on. If it really gets to the point I need to set up a fan system to pull outside air into the "Box" then perhaps it's time to pull the plug.

Eliminating other items on your list is also important, you mention ice buildup on top of the container, how confident are you of the integrity of the container roof? Ice can reveal issues not seen during rain as it can melt over long time periods and it’s like having rain all day for a long period. Looking at pictures of shipping containers it seems doubtful this is your issue, unless you have physical holes as a leak on the side of the roof panel would likely run down the internal wall.

I've been in and out of the container for months and months now, and never once seen a drip of water fall from the ceiling until this most recent issue.

I am concerned about ice build up and pooling water on the roof though. If I can do it on a budget with external timber and some cheap corrugated material, I might install some kind of roof to minimise the issue.

Did you take any pictures during the fit out? May help the grey matter be clear on what you’ve done.

I did, I have a lot of photos but none of them are great tbh. This should give you an overview:

Another way to confirm your suspicions is to cut an inspection area out in the ceiling and take a look. If you do this don’t be surprised not to find precisely what you were after. I had a leaky bathroom ceiling for a while and I cut a hole only to eventually find the leak was 2m away, the water was just pooling and dripping where it found the path of least resistance. It should however let you see if the container roof is wet with condensation.

Thinking about the above posts a form of positive airflow would be a good option. Someone on here installed computer fans in their underfloor void to guarantee airflow. Opening a vent on one side and installing a fan at another location to force air through the cavity could be really successful. I’d blow into the cavity, rather than suck out from it. You want a positive pressure in there so any air leaks into your box, rather than a negative pressure and any air leaks pulling moist air out of your box.
Fitz.

I have pulled down the boards closest to the big double doors, that's how I know how bad the problem is. Every insulation board that I took down let out a big pool of water. I think if it was a leak, rather than a condesation problem, it would probably have it more concentrated where the dripping was happening. There isnt really any way the water could get from roof section to the other if there was a leak, due to the corrugation, it would be limited to either dripping down the walls (no evidence so far) or pooling on the low spots and dripping on the ceiling. The condescation is pretty visible tbh. Don't worry about the rust, it's all just surface stuff.

How about some mushroom vents as seen on caravans

Or a swirl vent you see spinning on top of vans. They create thier own airflow.

Or another idea is a cowling made from 100mm 90° pipe bend fixed in a nw direction as the prevailing winds come from the SW.

Has the window at the front got trickle vents if not get some and fit.

Cheers James

The window does have trickle vents, so I will make sure they're open today as that will help.

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.

I suppose I could possibly install a fan on the big one, but I guess I can also add that later If I find I need it.

 

[Woody2Shoes]

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

I think that the difference between a house and a container is that in the house there are cooking/washing activities that put more moisture into already warmer air. In a container, the only major source of excess moisture (assuming the materials inside the container are of low moisture content) is humans breathing/sweating into warmer air - and the fact that, at night, the metal sides and particularly the roof, get rid of heat very fast and create a cool surface for just about any airborne moisture to condense out. I think this condensation will happen even without excess moisture being added, depending on the weather conditions - hence ventilation being helpful, not in preventing the condensation happening, but in letting the condensate evaporate away again as temperatures change for the better. The other option, which may not be practical, is to make the space on the cold side of the insulation completely vapour/gas tight. My local merchant often delivers carcassing timber which is sopping wet (kiln-dried, yard-soaked!) - I do wonder how much of the moisture in the photo came from the timber.

I have a 20ft container - unheated and unoccupied though - and I am very careful of what I put into it (e.g. only very dry timber) and have had no condensation problems. Mine has four tiny cowled vents at ceiling height near each corner - I think these help, but they don't need to work very hard most of the time.

 

[Peri]

I don't know if this helps, but my workshop is a single garage, away from the house with iron corrugated sheets for the roof. I've been in it every day this week with the big up-and-over door fully open all the time was in there - and I still had one day when I had water dripping off the ceiling.

In the last 10 years its happened 3 times that I remember - so maybe when it does dry out, it won't be something that happens all the time?

 

[PJBuzz]

I don't know if this helps, but my workshop is a single garage, away from the house with iron corrugated sheets for the roof. I've been in it every day this week with the big up-and-over door fully open all the time was in there - and I still had one day when I had water dripping off the ceiling.

In the last 10 years its happened 3 times that I remember - so maybe when it does dry out, it won't be something that happens all the time?

You could well be correct, although i think there is a good chance that there has been a build up on the inside that only made itself clear when it got ot he point that it dripped through the small gaps in my insulation barrier. It could well have all happened in one night, but the more I thibk about the last few weeks since I have installed the temporary electrics and the heaters, the more I think this is just a result of my own ignorence.

Now that I have read all of the information on condesation, it all seems so bloody obvious, and it makes me feel like a bit of an *****.

 

[Gavlar]

From a perspective of one who works in shipping/container handling...condensation can be a cause of cargo spoilage when the vents get blocked, so it's imperative they are kept clear. By all means add more. If the insulation foam is hard up against the box wall, this will create a series of vertical channels, most of which are unvented and contributing to the problem. I'd suggest spacing the foam away from the wall to create one large air gap, which you can force-air ventilate, although obviously that would mean moving the framing and ply inwards a bit. The dehumidifier is a good option as well, but doesn't address the root cause.

 

[Dovetaildave]

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 ;

 

[PJBuzz]

From a perspective of one who works in shipping/container handling...condensation can be a cause of cargo spoilage when the vents get blocked, so it's imperative they are kept clear. By all means add more. If the insulation foam is hard up against the box wall, this will create a series of vertical channels, most of which are unvented and contributing to the problem. I'd suggest spacing the foam away from the wall to create one large air gap, which you can force-air ventilate, although obviously that would mean moving the framing and ply inwards a bit. The dehumidifier is a good option as well, but doesn't address the root cause.

Hi Gavlar,

Certainly great to have someone with first hand experience onboard!

The insulation boards sit inside the framing, and don't touch the metal anywhere, at least if they do it would only be very slight. The wooden beams touch it in a couple of spots, but not enough to isolate a large panel from airflow. In general I think the space around the outside of the "box" is a good few CM all around.