The ultimate guide to shipping container condensation treatment options.
Do you need to store fabrics, textiles, artworks, foods, shop stock or other very moisture sensitive goods in your shipping container? You might like to consider some of the shipping container condensation treatments available that we can supply and also a few DIY options that may help.
You can click on any of the links in this article to see more about each product or process elsewhere on our website which will include example photos and more details on the product or option.
Why, when and where does the condensation come from?
When a shipping container cools overnight the heat escapes (usually through the roof), the air inside cools, and the water in the air condenses (turns into drops of water) and this will build up on any surface that the heat is escaping from – this is why you may see it on your container roof in the mornings.
On a hot summer day you may find that the sun will heat up the roof of the container and allow condensation to evaporate back into the air inside the container relatively quickly.
The amount of condensation will vary depending on a large number of factors – for example:
- Air Space: How much air space there is inside the container (how full of goods it is). The more air you have in your container, the higher the potential there is for condensation.
- Temperature: How cold it gets overnight, and how quickly it gets cold. Also the direction of prevailing wind and how exposed your container is will also make a difference e.g. on a clifftop versus tucked away in an alleyway between 2 warehouses or industrial units.
- Ventilation: The more air you have circulating within your container, the smaller the difference between inside and outside temperature, which in turn will reduce or prevent condensation.
- Goods moisture content: If, for example, you load your container with wooden crates of goods, but you loaded it in the middle of a thunderstorm, any water that fell onto these crates now sits inside your shipping container and when it gets hot this water will evaporate, and when it cools this water will condense again.
- Usage: How often are the doors opened, how frequently the container is loaded or unloaded, the time of day & weather conditions when the container is being used. These circumstances can also affect the amount of moisture in the air inside your shipping container, which in turn will affect the amount of condensation you can get.
Newer containers and containers with more vents will perform better, but you should expect some condensation in your shipping container unless you take steps to prevent this.
So if you are reading this page, chances are that you are storing some goods that you think may be at risk in your shipping container if you don’t treat it. Below we detail the main types of condensation treatment available, including options available through us and for DIY options we have seen in use.
Can I buy an insulated shipping container?
Insulated shipping containers used to be in common use about 25 years ago but were largely phased out by the 1990’s. They were mostly used to move freight that didn’t need to be refrigerated or frozen, but needed to be protected from extremes of weather e.g. fruit, veg and other fresh produce.
Insulated shipping containers also fell out of favour with the shipping industry as refrigerated shipping containers improved and became more commonplace. These refrigerated shipping containers could offer better levels of insulation but also offer atmospheric controls (temperature and humidity) making them the choice container for frozen, chilled and ambient goods as well as industries that might want to ensure their freight never goes below a certain temperature, for example the pharmaceutical industry. They can be used without power as a basic insulated unit or they can be powered for a whole host of other options.
We have not known of any insulated shipping containers coming onto the market from shipping use for a number of years, so if you find one advertised we would suggest it’s very old and best avoided. In this guide we detail the range of insulation options available for any shipping container, and pros and cons of each option or process.
Non-Operational Refrigerated Shipping Containers (AKA ‘non-op reefers’)
Pros: Best quality of insulation available, purpose built unit. Food grade interior
Cons: Very difficult (expensive) to modify the structure on one of these containers, very limited availability
Non operational refrigerated containers are available, but very rare. A non-operational refrigerated container has had some form of damage occur that makes the engine non operational. At the same time the structure or frame of the container must remain in good condition. The engine needs to be damaged enough so it’s not cost effective to repair – this is the main reason why these non-operational refrigerated shipping containers are so rare. There are only 1 or 2 parts in a refrigerated container engine that may fail that would likely make it not viable to repair if it’s near the end of its useful life. Typically we see a handful of 20ft non operational containers in the UK every year, however 40ft non operational containers we currently have good available stocks of in Rotterdam that we can ship to the UK to order.
Top tip – if buying an ex-refrigerated shipping container of any kind only buy from professional, reputable sellers and we would recommend making extra efforts to ensure it’s sourced directly from a shipping line or leasing company.
It’s very easy for a small pinhole to appear in the outer skin, perhaps on the roof area if the container is not well maintained. This can very quickly allow the wall cavity (which is stuffed with insulation) to get waterlogged. All of a sudden your container now weighs 8-10 tonnes when it should otherwise weigh around 4 tonnes. It won’t’ insulate your goods very well. It may start leaking inside and at this point you have the worlds most expensive paper-weight (it’s otherwise pretty useless, and will have likely negative value – ie.: you’ll likely need to pay someone to take it away and dispose of it)
Disposing of a refrigerated container is also not straightforward. Scrap yards will commonly charge you for the disposal as the work involved to safely break it down will usually exceed the value of any metal left inside the container itself.
Pros: Very good quality option, always available.
A lined and insulated shipping container is a very good quality option and if done well should offer a very long term solution (10 years +) for your container. This is an option we can offer at the majority of our depots, and its also a job that a relatively competent DIY-er can take on.
In basic terms, a frame is built inside the container, and ply sheets (or any other wall surface / paneling of your choice can be used) are fixed to this frame. The cavity (gap) between the internal wall and the outer shell of the shipping container is stuffed with insulation material (rock-wool as a basic option but any insulation material can be used). This dramatically slows the rate at which heat escapes from the container, which if built well will prevent the condensation forming. Even if not built / insulated well the internal roof paneling will prevent any condensation reaching the cargo space.
Specs and costs can vary a lot as we can vary the paneling type and thickness, and the insulation material can also be customised. (One customer may want an expensive, but thin insulation materiel to help us maximise internal space for a specific item or container use, another customer may just want the most cost effective option.) As a rough guide though this is one of the more expensive options out there in terms of upfront cost. We would estimate a ball park cost of £1000 per 20ft container / per 20ft section if we are to offer a ply line and insulate option, or circa £500 in raw materials costs if taking this on yourself.
Top Tips if looking at this option
- When available, a non-operational refrigerated container will offer a better level of insulation and should come in at a similar overall cost. If available at a similar price, and if you are not converting it we would usually recommend a non-op reefer over a ply lined container.
- If doing a DIY job, make sure the roof is done very well, its this panel that looses the vast majority of any heat, so it’s this panel you want well insulated over any other.
- Prices can vary with specs. 6mm ply is obviously a lot cheaper than 12mm thick ply – different suppliers will offer different specs to each other to match their own suggestions on value vs quality. We like to give you as much flexibility as possible to choose you own spec.
Pros: Relatively cheap, very effective and long lasting. Arguably the industry standard condensation treatment
Cons: It’s very nasty stuff to work with, its never coming off and often takes a few days to set properly.
Grafotherm is very much the industry standard condensation treatment, used not just on shipping containers but also aircraft hangars, warehouses, cold stores and sports centres.
You can get more info on what grafotherm is and how it works on our Grafotherm product page (link in title above)
Grafotherm is a very cost effective option, at around £200 + VAT per 20ft unit in our depots, or at around £75 + VAT raw materials costs (plus one off £50 on equipment needed if you don’t already have it).
Top Tips if looking at this option
- Grafotherm is horrible stuff to work with, we suggest only considering a DIY option if you have a lot of containers to treat.
- Apply grafo to the roof only and a couple of inches down the side walls at the top. Adding grafo to the inside containers walls is little more than a waste of grafo. (It serves no purpose and there is no condensation to suck up on the walls – condensation only forms on the roof)
- Great for the majority of ‘normal’ uses, storage of shop stock prior to sale, clothing, textailes etc – however we suggest less good for priceless 16th century artworks and ‘high end’ applications.
- Becomes useless if your goods are going to touch the roof of the container as the grafotherm absorbs the moisture so your goods will be in contact with that.
- Has been known to degrade when subject to extended moisture, eg an external leak in the roof of the container ‘flooding’ the grafo layer and being left this way for some time. When it degrades it turns into a pretty horrible porridge like substance and may then drop and fall over your container.
- It can’t be rushed, whilst the suppliers say it takes 10-12 hours to set, this is under very low humidity conditions and in a shipping container yard it’s not possible to leave your container to dry out in such an atmosphere. We believe it typically takes around 48 hours of plus 10 degrees Celsius to properly set. In summer this is little issue but in winter it may take a while to properly set or require heaters.
- Grafotherm is a commonly misunderstood product – at times even by those that sell shipping containers with grafo. it does not provide an effective thermal barrier to prevent condensation. It traps and holds condensation once it has formed. It will not remove condensation build up but control it.
Shipping Container Insulation Kits (New for 2018)
Insulation kits have been around for some time. These kits usually come in pre measured or pre-cut sheets to fit into your shipping container. These were popular with exporters of temperature controlled cargo that didn’t want to pay a premium for refrigerated transport.
Unfortunately the ones we have looked at in the past have been prohibitivly expensive. As these kits were not made in the Uk and there was no UK distributor this meant supply and distribution was another big barrier to these being a viable option for shippers. Other issues includes the thickness of polystyrene leading to a reduction of available cargo space, and the fact that refrigerate container exports from the UK are comparatively cheap (as there is an imbalance of imports, lines will charge you less if you are helping them ship an empty container out of the UK) At some point these kits needed to be cheaper for exporters than the price difference in shipping a refrigerated container. Until recently in the UK at least this hasn’t been an option.
Fortunately we are now able to offer supplies from UK held stock of our top quality insulation kits. Made from layers of laminated foil and insulation, these 4mm thick sheets perform about as well as 55mm of insulation, plus they come in at a viable price for both exporters and storage container owners. (From £200 + VAT for a single 20ft kit)
For exporters of temperature sensitive cargo we can offer some higher grade insulation kits. For customers wanting to prevent condensation build up these basic kits will work fine.
These insulation kits take 2 people approx 30 minutes to fit and require no special tools or equipment. A broom can make life easier when sticking the fixing tape to the walls and roof of the shipping container. The internal container walls will need to be clear and free of any moisture or dirt when fixing the insulation kit.
We have our 20ft insulation kits and 40ft insulation kits on the website (including high cube options). At this time we cannot offer kits for other sizes of shipping container unless its a big enough bulk order to get the manufacturer interested, although in some cases you may be able to ‘overwrap’ a 40ft kit into a 30ft container and similar.
Shipping Container Damp Sticks
Pros: Great temporary solution, as easy to use as it gets. Great for a 3-6 month project or a single import or export shipment
Cons: Not cost effective for permanent or long term use.
We offer 2 types of Damp Stick on our website, we have the Absorpoles and the Bone Dry Dampsticks. Both do a very similar job as as far as we are aware and are very similar products in terms of effectiveness.
Working very much in the same way as the silica gel packet in a new handbag or briefcase, these suck up, trap and hold any moisture within the damp-stick itself, each damp-stick comes with hooks to you can easily hang them onto the cargo lashing points in your container. They are 100% non toxic and the main ingredient in these is starch.
These are a temporary solution, each dampstick will last around 12-14 weeks / 3 months – meaning their primary purpose is for use within the export industry to keep perishables free of moisture for a week or two whist they are shipped around the globe. They are also recommended for house renovation jobs (where you may want to hire or buy a container for 3-12 months to store your stuff in whilst you undertake some major works to your home.)
Top tips if looking at this option
- Make sure you have regular checks in place to make sure they haven’t run out of absorbency. if your goods are going to get ruined it can be a very expensive mistake.
- Make sure you have spares, if you find they have run out you will likely need to replace them promptly. Despite our prompt delivery service we wouldn’t want us being out of stock meaning your goods ruin.
- Each pole come in its own bag, do not open the bag until you want to start using the damp-stick, otherwise it will start sucking in moisture from the moment you take it out of the bag and you will be at higher risk of splitting or puncturing the bag.
Pros: Work in the same way as Damsticks but they are cheaper
Cons: Temporary solution only. Not cost effective for long term use.
Also fine to use in a storage environment, these work out as the cheaper but less pretty option when compared to damp sticks. They contain very similar non toxic desiccants which soak up any moisture from the air and will typically work for 12-14 weeks or until full. Currently we advertise the hooks on our website as a cost effective alternative to the damp sticks, but we can advise on the best solution and offer alternative desiccant options for large volume exporters who need to keep their goods from from condensation and potential water damage.
As with the damp sticks, these are a temporary solution. Great for use in storage containers being used for short term projects, or for exporting moisture sensitive cargo. We don’t’ typically recommend these as cost effective for a permanent condensation treatment solution.
Pros: A very cheap and easy option to set up in a domestic environment
Cons: Often only viable or cost effective in a domestic setting with someone confident about setting up external power. Ongoing power costs make this less cost effective the longer its in place.
Many customers have suggested and tried running their own de-humidifier inside the container. This work very well in a home setting if your container is accessible to a nearby power source and if you have a dehumidifier. Commonly, the health and safety requirements to undertake this as an option in a commercial or industrial setting may not be practical or cost effective.
Setup simply involves running domestic power into the container (you can drill through the side walls in a container above the internal floor line pretty easily, put your power cable through and plug up any excess hole to stop any weather getting in).
Typically in a commercial or industrial setting one would require a qualified electrician to install this equipment to meet health and safety policies which will often make it an expensive option compared to say Grafotherm. This advice is given only on the basis that you are happy and capable of setting this up safely in your own home. We take no responsibility if your try this and there are issues due to unsafe electrical work, with equipment not being set up properly or similar.
Top tips if looking at this option
- Check the dehumidifiers instructions carefully before use. Ensure its well vented, regularly checked and emptied and installed properly
- Make sure you can get at the dehumidifier to empty water out and / or maintain it
- Use good quality shielded outdoor power cable where possible.
- Ensure you have an RCD safety cutoff on the electrical circuit at all times.
Pros: Simple, cost effective,
Cons: Great way to significantly reduce condensation but we can’t guarantee zero condensation. Vent gaps may let in small numbers or very small bugs and insects into the container.
In a very well ventilated shipping container, the air inside the container will maintain a temperature very similar to the outside of the container, thus reducing or completely removing any condensation build up. Its is an inexact science, we can’t tell you for certain that XYZ area of vent will remove any condensation from a 20ft container as there are a lot of other factors involved.
Generally if looking to add your own vents there are 3 main options
- Basic standard shipping container vents
- Larger Louvre vents
- DIY budget vents
These are quite small, circa 1 inch square and there are usually 2 or 4 of these vents on a standard 20ft shipping container, 10 vents are included on our high spec new build option.
Our general advise, these vents aren’t great in terms of letting good volumes of air through your container, although they are great at keeping bugs and insects out.
These are much bigger than the basic vents and we would suggest a much better option if you are planning to use ventilation to significantly reduce or remove any condensation build up. These have bird mesh to prevent small animals getting in but this mesh isn’t 100% bug and insect proof.
Budget DIY Vents
Off the shelf vents always offer a good quality option, but for some circumstances a cheap and cheerful option is needed, here’s one simple trick to vent your container for around a fiver!
- Find an inner corrugation on your container, ideally at the top of the container. Add drill holes liberally / as required
- Fix a plate over this area between the 2 outer corrugations either side of the hols you’ve drilled, covering the vent holes from rain, but leaving a gap at the bottom to allow free air flow
- This will allow a fair rate of air flow whilst also protecting the area from wind and rain getting in
- You may wish to further add mesh to help keep out bugs and insects.
Other rooftop thermal insulation options
We have also seen a lot of DIY as well as professional jobs where the roof of the container is one way or another insulated to slow the rate of heat loss, which in turn will reduce or remove any condensation build up.
Examples we have seen include
- Gluing or fixing insulation material to the inside of the container roof
- Adding layers to the outside of the roof and then sealing it to stop weather egress into the new roof.
- Doing your own ply line and insulation job but only working on the roof area.
- Chemical or foam sprays or similar insulating material applied to the inside or outside of the container to limit thermal loss (and thus reduce or prevent condensation forming)
How well it works depend on one thing alone – how much slower will the heat escape from the roof of the container. if you can drastically reduce the rate at which heat escapes, you can significantly reduce the condensation build up inside. There it no correct way to achieve the end result when there are a thousand different ways to approach a problem, and when some solutions will work for some customers better than others.
We are regularly approached by different companies offering various options for some form of insulation layer that will usually prevent condensation forming. We stop short of detailing a lot of these options as to date we find the vast majority are not cost effective when put against some of the other options shown here. Many are more expensive than a ply line option (unless looking at significant volumes), many of these products have restrictions on when we can use them (eg a high operating temperature range would prevent us offering some treatments for 8 months of the year). We will however update this article with any new products we see hitting the market that we feel will likely remain popular.
If you’re looking for further advice on whether material you have to hand might work or not, sorry we are unlikely to be much help. We’ve listed our own tried and tested methods, and we’re obviously unable to comment on the effectiveness of a treatment option or material that we haven’t got a good base of experience with.
We understand there are a few companies offering shipping container insulation services for containers (as well as serving other industries) these treatments we believe by and large offer a very good quality option, but methods we have reviewed typically come in a lot more expensive than a Grafotherm option and sometimes come in more expensive than a ply line and insulation option.
Need a condensation proof shipping container?
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We can apply condensation treatments like grafotherm or ply line containers in nearly all of our depots.
Or of course you are always welcome to contact us, where we have a helpful team on standby 08:30-19:00 weekdays.