Need a retreat? For teenagers to in-laws, Granny Flats are great to let those you love have their own space. And you’re in luck because you can buy a container or two and build her a little home that’s just the right size for her. This article will guide you through everything you need to know about building a Granny Flat.

Building Codes and Permits

Even though the granny flat will be on your property, it is still a good idea to know what the building codes are so there aren’t any unpleasant surprises later on. After getting up to speed on the building codes, it’s time to get all the building permits you will need. Building without permits can be costly, both in terms of money and lost time.

Architectural Planning

It may just be a granny flat, but it needs the same amount of planning a regular house does. You will have to figure out where the rooms will be, along with how many. Most of these small homes have a kitchenette, a full bathroom, a bedroom, and a living room. Depending on who it’s for, you may also need a small laundry area, too.

Structural – Unless you plan on hosting barbecue parties on the roof,  there won’t be a need for any special structural reinforcement. The vast majority of granny flats are single-level, usually constructed with one 12-meter container.  If you opt for a double-wide design, then you will need to install a weight bearing beam that is wide enough to provide support for the entire length of both inner container walls. Openings in walls for windows, doors, such won’t require additional support unless you intend to install a roof structure of some sort.

Container Preparation

Now that all the planning and permits are in place, it’s time to prepare the containers for becoming a new home.

Prepaint Preparation

Before grabbing the paint gun, make sure you follow all the steps to prepare your container for painting:

  1. Remove Stickers–If you plan to repaint the exterior, you will want to remove the stickers. If a razor blade isn’t doing the job, a heat gun or handheld hair dryer can be used; just heat up the sticker then pull it off with your bare hands. If you are planning to side the granny flat, this step is unnecessary.
  2. Wash–Power wash the containers with an acid wash, then rinse thoroughly. Allow to completely dry.
  3. Inspect Container–Carefully inspect the container’s exterior, including the top, keeping an eye out for moderate to severe rust. You may want to bring along a pocket knife or screwdriver to flake away blistering rust. Use the knife to remove some of the rust. If the exposed rust is bad, make note of it. Complete your inspection of the exterior, then look around inside for signs of water leaks or seepage. Note where all leaks are for patching later on.
  4. Rust–Remove surface rust with a grinder. For heavy rust, you will have to patch it. Small areas of rust can be knocked out ground to clean up the metal. These small areas can be patched with a welder using a low alloy filler. The alloys in the container steel will mix with the filler, giving it the same weathering properties as the weathering steel itself. Areas too large for filling will require a piece of weathering steel cut to fit.
  5. Primer–If you plan to use the container’s exterior as the exterior of your home, it is a good idea to apply primer to the container. This will help the finish coats of paint to stick and last much longer. Be sure to pick a primer that is right for the paint you will use.


Steel structures are notorious for absorbing massive amounts of heat. To counteract this characteristic, use a light-colored, reflective alkyd enamel paint. If you are looking for optimal heat reduction, then you may want to consider coating it with Super Therm®, a water-based ceramic coating that reflects 95% of the heat that hits it.

Paint can be applied in two basic ways: by spraying it on or by rolling. Here are some things to keep in mind when painting:

  1. Spraying–You will have to thin down the paint enough to get a good flow through the sprayer. Apply at least two thin coats using an even back-and-forth motion.
  2. Roller–This method does not require you to thin the paint. Before rolling, use a paintbrush to block in all corners and edges, brushing on a light coat of paint. Roll on a thin coat of paint and let dry. Repeat this process of blocking in and applying paint. Use a minimum of two coats.


With planning complete and all tools and materials on-hand, it’s time to start building. There are a few things you must do setting the container and building:

  1. Plumbing and Electrical–Make sure you have sewage and electrical (if needed) installed and ready for pouring.
  2. Concrete Slab–Pouring a concrete slab that is to code will provide a stable, level base for your granny flat. Before setting the container on the slab, you will need to install a moisture barrier and some kind of insulation. This will help make the granny flat easier to heat and cool.
  3. Anchors–You may want to anchor the granny flat to the concrete slab. This is easily accomplished with some concrete anchors, brackets, and bolts. If you plan to anchor the granny flat, be sure to do that after the container is set but before you start building. That way, you will have an easier time running bolts through and fastening them.
  4. Cut all Holes–Measure off and cut out all holes you will need for windows, doors, heating and cooling, ventilation, electrical supply, water, and sewage.
  5. Building–Framing in walls, wiring, plumbing, and other construction tasks can be completed the same you would if building a regular home. If you happen to get stuck on any of these tasks, there are countless resources online to help you out.

Now pat yourself on the back for a job well done!