A shipping container is a super unit to store your items in, with a massive volume, they are strong, sound, and with a lock box fitted very secure. But without the use of precautionary measures do have the possibility of creating condensation.
The value and type of your items, the period length of storage , where the container is placed and of course your budget, will determine how much of the below information you wish to put into practice and what extras you may wish to apply.
The best type of Shipping Container to use for storage is an insulated one, these can be purchased New or ex shipping line but are very expensive .The value of the insulation is the protection from ambient temperature exchange from external to internal, it is this exchange that can cause the condensation and damp. A bright sunny day in the middle of winter, will warm the roof of a container to significantly increase the internal temperature to an active humid level the subsequent cold night air will then lower that internal air temperature ,releasing the moisture as condensation.
Storing your shipping container in a barn or warehouse, will lessen the effect of ambient temperature exchange. If you have purchased or rented an Insulated container you can insulate yourself quite effectively see on www.containersforsale.co.uk subject ... Insulating a Shipping Container.
BUT what ever your storing, and in what ever type of container, standard or Insulated , always, always, always use The Dampstick Poles , or similar methods when storing in a Shipping Container.
Before you store your items in a Shipping Container, check the interior is dry. Check that it has no holes in roof or side walls, or likely to develop them. get someone to shut you inside, allow your eyes to adjust to the dark and slowly with one hand on a side wall, move to rear of container across and back to doors , if there are any holes they should become apparent by this method.
Check that the container door seals are secure and weather proof. They are a dual seal, the outer flange prevents water getting in by wind or wave, the inner seal prevents any water that may have passed the first seal entering the container and should that happen, it sends that water by drainage around the door frame to drain out of bottom, so check the top and side seals are free and clean ,not full of crud that will prevent their draining off.
The container should ideally be raised off the ground to promote underside airflow, which will help to keep the underside floor dry and it should also be placed very slightly higher at front than the door end, this simple measure will allow any water that may have got in or leaked to come to the rear door end and you will see it, rather than it continuing to form a puddle at the back that you that will never notice and creating any amount of condensation without you realising why.
If the container is New or Recently manufactured it will most likely have a Kiln dried ply floor, and will not require covering, ( most Containerised Self storage companies have new build containers ) but, if yours is a Used Ex Shipping Line Container it can easily have without appearing damp a surprisingly large amount of moisture trapped in the 28mm thick Ply Flooring! To combat this trapped moisture, cover the whole floor with a Barrier Foil. These are available in a variety of thicknesses and comprise of a hard wearing foil upside and downside a waterproof membrane to prevent ingress. Barrier Foils are used extensively when Shipping Tea or other very moisture sensitive items and are very cheap but effective in the prevention of moisture evaporation from timber floors. The sheet or sheets should be laid flat covering the whole floor and duck tape sealed around all perimeters. See www.protpack.com for an example of products. (If you purchased your container from a reputable supplier they should be able to assist in supply of these, if they cannot contact www.dampstick.com we will help you source).
Once the floor is satisfactory, tape up the containers vents. These are usually found high in the corners of the container and from the inside they look like a series of drilled holes. With a good quality tape, cover these over from the inside , they should not ordinarily allow any water into the container, but they will allow damp air, so make sure you have a good margin of tape around the holes as the damp air will lift a meagre amount of tape off.
We recommend initially placing at least two Dampstick Poles in a 20’ container and ideally they should be placed equidistance in the container, but if your storing for a long time you will need to check and exchange the used Dampstick Poles so you will be hanging them close to the doors, make sure you have hooks to hang them on, almost all Shipping Containers have these in the ceiling perimeter and also on the floor for cargo lashing, but if in the unlikely event there are none, go to your local hardware store and buy good quality stick on hooks. (check the weight recommendations )
Now check all the items you are going to store are dry, that means if your storing household effects, emptying clothes washing machines /dishwashers of water and checking the pipes are empty…Remove from fridges and freezers all moisture and ice, any damp object wherever its placed in the container has the potential to cause condensation or mould so be thorough in checking for damp items.
Select the items that you are least likely to want out of the container and put these in first. To utilise the cubic capacity, put small items in drawers and wardrobes and make a list of them. Pack all books and small items in good quality cardboard boxes, ex supermarket boxes may have more water contained in the cardboard in them after they have been used, so be selective or buy new.
Do not put mattresses or soft furniture in plastic bags even if made for that purpose, they will warm up and draw the moisture out of the mattress and cause mould and yes your mattress does have a lot of moisture in it ! Best to cover these sort of items loosely with old blankets. If the container is going to be filled right up, leave an air gap at the top between your stored items and the ceiling of about 9” throughout this will allow the The Dampstick Poles to operate efficiently on all the air.Lastly, your Dampsticks, where to place them ... Ideally they should be placed front and rear one each side, but realistically most people will store as much as they can in the container and therefore the next best position is either side at the rear doors. This will enable you to periodically check that they are not full.