It won’t matter how good your shed is if your base is rubbish. Most people do not give too much thought to their base, but it will add many years onto the lifetime of your garden building.
What is a Shed Base?
Shed foundations are essential for every shed. You wouldn’t build a home without first constructing a solid foundation; well the same applies to a shed. As we have already mentioned, a shed needs to be assembled on a firm base or all manner of problems will ensue, so whatever type of shed you are building, a stable base is essential. Sheds can be erected without a solid foundation, but they don’t last long and are rarely strong enough to cope with the elements. Placing a timber shed directly on to the ground is a bad idea. Moisture will permeate up through the timber and cause the wood to rot. This won’t happen overnight, but over time your shed will begin to collapse from the base up.
Is Planning Permission Necessary?
It is not normally necessary to apply for planning permission before building a timber shed, but if you live in a conservation area or the shed is larger than normal, check with your local planning authority to be certain.
You should always check with your HOA and municipality as there are often stipulations on size, location, aesthetics, etc.
Different Types of Shed Bases
There are several different types of shed bases. Some are more robust than others, but ultimately the shed base you choose will probably come down to how you intend on using your shed, what type of stuff you are planning to store in your shed, and how much time and resources you have at your disposal.
Larger sheds, such as outdoor workshops or home offices, will require a concrete foundation, but if your shed will primarily be used to store garden implements and tins of paint, there are other quick and easy options available, including a plastic shed base, which are less labor-intensive and quicker to install.
Concrete Shed Base
Concrete is by far the best shed base for larger sheds or sheds containing heavy equipment. Providing you have prepared the ground properly and chosen the right location for your timber shed, a concrete foundation will offer ample support to any size of timber building and should last for many years without needing to be replaced. This is a fairly labor-intensive option, but well worth the investment.
Once you have decided where to place your shed, using strings and pegs, measure out a shed base that is 2” wider than the actual shed. dig out the soil, rubble, and turf. A concrete base needs 3” of crushed hard-core as a foundation, so you will need to dig down around 6”. Once all materials are removed, make sure the base is level and remove the pegs and strings.
You will need to build a timber frame to make sure the base is the right size and shape to line the edges when the concrete is poured. Any straight pieces of timber are fine. Measure the base and cut out four pieces to size. Use a spirit level to be sure that that all sides are level.
Spread a layer of gravel, stones, or crushed ballast inside the timber frame and compact down until it is flat. Use a compacting tool for the best results. Cover the hard-core layer with a generous amount of sand and level it out.
You can either mix your own concrete or have it brought in. Spread it out evenly. Once the concrete is at the required level, use a piece of timber to smooth it off. Check frequently to make sure your base is level and if need be, add more concrete. Concrete needs at least 24 hours to fully set. If rain is forecast, cover the concrete with a plastic sheet to protect it. In warm weather, place a damp cloth of sacks over the concrete and sprinkle with water to prevent the concrete from drying out too fast and cracking. Once the concrete shed base has completely dried, you can begin to assemble your timber shed.
Slab or Paving Stone Shed Base
A slab or paving stone base makes an excellent foundation for a shed and is a popular choice for smaller garden sheds. As with a concrete base, location is all-important, as placing a shed on the uneven or sloping ground will result in an unstable shed. Any paving stones can be used as a shed base, but thicker slabs are less likely to crack under pressure and will provide a more stable base. Make sure the paving stones you buy are all the same depth
Use strings and pegs to mark out an area approximately 2” wider than the base of the shed. Dig out the soil, topsoil, or turf down to a level of 2 ¾ inches. Once you have excavated the recess, remove the strings and pegs. Mix together one part cement and eight parts sand thoroughly. Pour the dry mix into the hole and spread out evenly using a rake. You will need about 1 ½ inch of dry mix. Make sure the cement-sand is nice and level. Starting in one corner, take a paving slab and lay it down carefully. Use a rubber mallet and tap the slab gently. Check whether the paving stone is even with a spirit level and move on to the next slab. Take your time laying the stones. Keep checking whether they are evenly laid and butted close together. When finished, take a step back and make sure the paving stones are straight and level, if not make the adjustments needed. Brush the surface and remove any excess cement and sand mixture. If there are any gaps between the stones, add some more dry mix to plug them.
Slabs can be prone to settling, so make sure that the ground well compacted before laying. Also, you do not want to lay slabs near trees, as roots will push them up easily.
Plastic Grid System
Plastic grids such as EcoBase or ProBASE are a great alternative to paving slabs. A plastic shed base is a relatively new option for forming a shed base but is one that has definite advantages. The base is typically made from a series of plastic grids. The squares are made from a very durable, tough type of plastic that comes from recycled sources. They are used in exactly the same way, however, they are lightweight and therefore much easier to handle, can be cut and shaped using a normal handsaw, don’t transfer dampness, and have air cells throughout allowing your building to stay nice and dry. Because of their open design, plastic grids are not suitable for buildings without structural floors. Please note that you should choose a large grid at least 20”x20“ as smaller grids are prone to a lot of movement.
Clear the shed site and is level. There isn’t any excavation required. Next, lay down a layer of landscape fabric or geotextile. This will suppress the growth of weeds below your new shed, which in itself can be extremely beneficial since weed growth can damage your shed by allowing intrusive moisture to damage it from below. Sizing the blocks that are used to build these bases is one of the easiest parts of the process. All you have to do is take a handsaw and cut the grids to the size you need. The grids are interlocking and so are quick and easy to assemble which makes them a great time saver. After you have placed your choice of suppressive fabric you then place the grid pieces that you have cut to size. They fit together quite easily and you will then just have to fill them in with pea gravel. You can then build your shed on the surface.
Makes it more difficult for rodents to get in your shed, allows for ventilation, plastic will not rot, will not hold moisture, UV stabilized.
Timber Bearers
For a quick, easy, and inexpensive way to create a secure base for a shed, create a foundation using pressure treated timber bearers. Pressure-treated wood is resistant to rot and will last for many years. As such, it is a good base for a shed. However, this method will only work if you have a level area upon which to construct your shed. Any major lumps and bumps will make it difficult to achieve a level foundation.
The bearers will need to be placed beneath the joists of the shed. Bearers should be positioned every two feet, so use the dimensions of your shed to work out how many bearers you will need. These can be brought from any timber merchant. If the ground is slightly uneven, extra support can be provided in the form of old paving slabs. Place the paving stones in areas where the ground is lower.
Timber Decking Shed Base
Timber decking makes an attractive and solid base for a wooden shed. For small sheds, erecting a section of timber decking might be more expensive than the job warrants, but if you are planning to use your shed as a summer house or children’s playhouse, an extended area of timber decking will provide an attractive veranda area.
Clear out and level the site you intend to place your shed on. Cover the site with a weed control membrane. This will prevent unsightly weeds from growing back under the decking when it has been completed. Always buy a good quality weed control membrane, preferably the thicker the better. Cheap membranes tend to break down after a few years.
Timber decks should always be constructed on-site because they are heavy. The outer-sub frame of the deck needs to be assembled first. Use countersunk coach screws to fix the frame at each corner after drilling guide holes, checking the angles each time to ensure a square fit. When you have built the other frame, cut your inner joists to size and fix them in place using pilot screws or galvanized screws. If you need to join joists together, use an offcut and fix it securely to either side of the joint using eight coach bolts. Deck boards should be fitted with a 3/32 inch gap between boards to allow for drainage and normal expansion due to changes in temperature. Use a deck screw as a spacer. The decking will be stronger if joints are staggered across the deck, but for a smaller deck, this shouldn’t be an issue. All timber that you use should be pressure treated so that it is protected against the weather.
If your shed site has a drainage issue, it can make your timber decking rot, even if it is pressure treated because it will end up sitting in water for long periods of time. To fix this issue, sit your timber decking on concrete pads.
Note, that you may have to add a set of steps to allow for access, as decking is often much higher than traditional shed bases. You may even need a ramp to be able to move lawnmowers in and out, etc.
In addition to shed bases, explore our article to learn everything about shed flooring.
