Converting storage containers: A guide

If you’ve decided to make use of converted storage containers as structures for your business, this guide will take you through the steps and considerations necessary to make it happen.

Design

Thorough planning is the key to a successful building project: while there will always be hiccups and unforeseen problems, you can cut these down to a minimum with plenty of preparation.

It’s important to work closely with your designer or architect to perfect the plan for your building. Most architects will use computer-aided design (CAD) to create a picture of the finished structure, which will help you to anticipate what you need before work begins. It will also allow you to make quick modifications to the design and try out new ideas.

Even if you are doing the design of the structure yourself, it is highly recommended to use a CAD package to pre-render the design in as much detail as possible. Work out the floor plan to the building and the conceptual design, taking into account all of the functional elements – utilities, space, sunlight, elevations and insulation are just a few of the considerations.

The finished design will detail what’s called the core envelope of the building: the exterior walls, ground floor, roof and glazing. Once you are happy with the design (or your contracted architect is), you can proceed to the next stages.

Planning permission

The wheels of planning departments can turn slowly, so it’s best to apply for planning permission as early as possible. Contact your local authority or visit their website for an overview of the drawings, documents and other information you will need to submit to them, and to find out the timeframes they tend to work to.

In some cases you may not need planning permission, particularly if the structure is an addition to existing industrial premises. If the building is intended to benefit the local community, you may also be able to apply under the Community Right to Build scheme instead of going through the normal planning process.

You may not need planning permission if:

  • An extension to a factory or warehouse covers less than 1,000 sq m of floor space and is less than 25 per cent of the volume of the original building;
  • The extension does not materially affect the outward appearance of the building, come within five metres of the boundary of the site, or reduce the amount of space for parking or turning vehicles;
  • It is a temporary building required in connection with ongoing works or undertakings, or needed to store external goods, materials and equipment;
  • In a private home, an outbuilding does not cover more than half of the area of the garden and is not more than 3m high with a flat roof, or 4m high with a ridged roof. It must also be used only by the occupants of the house.

If in any doubt at all, it’s always best to assume that you will need to go through the traditional planning permission channels. It pays to contact your local authority before beginning any structural work – and remember that paying for an unnecessary application fee is preferable to the hefty enforcement notice you could receive for going ahead without one.

Site preparation and logistics

Although transporting containers is usually quite straightforward, getting them exactly where you need them on the site can be more problematic. If stacking is required, or if the site is down a narrow lane or in a built-up area, you will probably need to use a crane to get the container off the delivery lorry and properly positioned.

Setting up a site for construction will typically involve the following steps:

  • An initial assessment of the site to find out if a site survey is required.
  • Survey of the site if required, and plans created to determine the delivery of the unit and position of the crane for delivery. It should also be confirmed that the crane being used can manage the load required.
  • Contact any authorities affected by the works - this may include electricity network operators if installation is likely to interfere with electrical power lines, or local authorities if roads need to be temporarily closed.
  • A method statement and risk assessment for the site should be prepared, outlining exactly what will be positioned on-site, when the works will take place and whether ground bearings are sufficient to bear the load placed on them.
  • Once the risk assessment and lifting plan has been completed, you will need to appoint a lifting team. This may comprise a crane supervisor, a slinger/signaller and crane operator.

All contactors involved at this stage of the project need to be certified by the Construction Plant Competence Scheme, which ensures they meet all relevant safety and competency standards. Using workers certified by the scheme may also reduce the environmental impact of your installation. If the supplier of your storage container(s) isn’t organising the delivery to the site, you will also need to source delivery personnel.

Any stacking should be carried out by trained professionals, as incorrectly stacking containers can have disastrous and expensive consequences. Stacking spikes are usually used to lock two containers to ones another, or alternatively, a steel frame is created that containers can be slotted and welded onto.

Foundations

Any permanent structure needs foundations to rest on. For a single container, you may only need some concrete or wooden supports in the ground, while a multi-container structure might require a whole basement. Consult a structural engineer on your design plans to find out what kind of foundations will be needed.

If you are using a poured concrete foundation, it’s advisable to plan on embedding steel plates into the concrete where the containers will rest, allowing them to be welded directly onto the foundation for extra stability. With multi-container structures, containers should also be welded to one another.

Cutting holes for doors and windows

An experienced fabricator and welder should cut doors and windows into the steel side of the container with a welding gun. Openings can range from a small porthole window to a fully glazed wall that can be opened to allow access to the entire side of the container. If the converted container is to be used as a food stall or ticket kiosk, you may want a sliding hatch that can be opened when the business is trading and securely closed when it isn’t.

Bear in mind that while storage containers are extremely strong in their original form, any cutting work will compromise their structural integrity. All openings for doors and windows should be reinforced by steel framing. In some cases, more reinforcement may be necessary, such as box beams to strengthen the roof.

If possible, due to the cost of framing, it’s best to have this done off-site before the containers are placed. Many suppliers have the facilities and personnel to make these modifications.

Cleaning, sanding and painting

Once the storage containers are on-site, they will need to be given a good wash down and any rust spots sanded before construction can begin. If you’re doing this yourself, use a high-powered spray brush to completely clean the containers inside and out; don’t worry about the floors, as they should be tough enough to withstand it!

During cleaning, take note of any rust spots or rust holes. These will need to be sanded down – it’s possible to do this by hand with ordinary sandpaper, but a power sander will get the job done more quickly.

If you’re just converting a single container for your structure, now is a good time to paint it. Use quick, even strokes from a spray paint gun across the surface of the container, and add a small amount of thinner to the paint to ensure even coating. You will usually need to give it at least two coats of paint.

Flooring

The wooden floors of shipping containers are usually treated with pesticides, so some people replace them, or form a physical barrier with epoxy resin and optionally build a new plywood subfloor on top of them. This may not be necessary, depending on the history of a given container (which you can find out by looking at its data plate).

If you are building a separate subfloor, seal the existing treated wood with solvent-free epoxy resin using a paint roller. You can then build a subfloor on top of this if desired.

Fixtures, fittings and insulation

In this stage you will set the glazing into the window openings and install exterior doors as required, as well as any skylights and flashing needed to weatherproof the structure. It’s also a good time to frame the interior, if desired: while not essential, framing and drywalling the interior creates a more natural (i.e. a less metal box-like) appearance, and can help with insulation.

Steel or wood studs, combined with spray foam insulation, can be used to secure drywall; include a thermal break between the studs and the metal container walls to keep the heat in. While expensive, a two-inch layer of spray foam also adds a bit of structural support to the walls and prevents condensation from building up.

Next, you can begin to install the plumbing, electrical and heating systems. Just as in any other type of building, wiring and plumbing should be only be carried out by trained specialists, but if you know where the holes are needed it’s easy enough to drill them in preparation for the work.

Once the main frame of the building is complete and your utilities up and running, you can begin installing the rest of the fixtures and fittings like partition walls, countertops, kitchen units and lighting. With these tasks complete, all that remains is the finishing touches – then congratulations, your storage container building is complete!