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What is the Best Shed Base?

12 November 2015 0 Comments
  • Timber buildings are incredibly useful. They are great as outdoor storage sheds for keeping garden and decorating equipment, old bicycles, pet food, and anything else you don’t have room for in your garage. Some people also use their shed as a bolt hole to escape into when family is driving them crazy. But whatever you use your shed for it needs to be erected properly from the get-go.

    Any mistakes made during the construction of your new shed will come back and bite you further down the line. A shed needs to be level and upright – if it is not level or upright you will have a huge problem fixing the various panels together, as screw holes will not match up. Any problems with the base will have a knock-on effect on the joints, which in time will compromise the structural integrity of the shed, eventually causing it to weaken and collapse. And if your shed has a glazed window for light and ventilation, the glass could crack or even break if the structure is not sound.

    Choose the Right Location for a Shed

    Choosing the right location is very important when you are constructing a shed. The ground needs to be level, so electing to construct a new shed on a sloping section of the garden will probably end in tears unless you are prepared to dig out a flat terrace. Sheds also need to be located away from foliage and mounds of damp vegetation and earth, or the wood will rot in time. If you are planning to add an electrical supply into your shed, this will also be a factor when selecting the best place to build your shed.

    What is a Shed Base?

    A shed base is the foundation upon which your shed is constructed. 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.

    Different Types of Shed Base

    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. Building a concrete foundation for a shed is fairly labor intensive, so it is always easier if there are two of you, but it can be done as a weekend DIY project for one reasonably fit person.

    Equipment Required

    • Building Sand
    • Cement
    • Hard-core
    • Pegs and string
    • Timber
    • Tape measure

    Once you have decided where to place your shed, using string and pegs, measure out a shed base that is 5cm wider than the actual shed. This is where the hard work begins, for you will need to dig out the soil, rubble, turf and whatever else is there. This can be done with a spade and wheelbarrow on hand to move the waste materials.

    A concrete base needs 7.5cm of crushed hard-core as a foundation, so you will need to dig down around 15cm. When you have excavated all materials, make sure the base is level using a rake and remove the pegs and string. If you want your shed to be raised off the ground, which is useful if the area is prone to minor flooding, you won’t need to dig down quite as deep. However, the hard-core and concrete base will still need to be the same depth.

    Make a Timber Frame for the Concrete Base

    To ensure your concrete shed base is the right shape and size, you will need to build a timber frame to line the edges when the concrete is poured. Any straight pieces of timber are suitable for building framework: old planks or similar will do just fine. Measure the base and cut four pieces of timber to size. Fix them into a rectangular arrangement, taking care to check whether the diagonals are the same. Place your timber frame inside the excavated area. Using a spirit level, check that the frame is level and steady – anything less will not be sturdy enough for your shed.

    Next, 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 best results. Cover the hard-core layer with a generous amount of sand and level it out.

    Mixing Concrete

    Concrete is mixed using one part cement to five parts ballast. Alternatively, buy a bag of dried concrete mix. There are two ways to mix concrete: the first involves mixing it by hand using a shovel, and the second involves hiring a concrete mixer. The first method is just as good as the second and is a useful way of getting a bit of exercise, but is more labor intensive. However, if you don’t have the energy, cement mixers can be hired easily enough.

    If you elect to mix your concrete by hand, add the water slowly and be sure to mix it well into the concrete before adding any more. The mixture needs to be fairly dry, so if it is too sloppy, add more dry mix.

    When you have enough concrete mixed and it is of the right consistency, pour it into your timber frame. Spread it out evenly and once the concrete is at the required level, use a piece of timber to smooth it off. Rest the timber on each edge of the frame and using a sawing action, smooth the concrete surface. Check your base is level using a spirit level and add more concrete if necessary.

    Concrete needs around 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 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. You don’t need to purchase new paving stones for a shed base. Instead, look for second-hand slabs to save money. Do make sure the paving stones you buy are all the same depth, however, or it will make life very difficult when you try to level them off.

    Equipment Required

    • String and pegs
    • Cement
    • Building sand
    • Paving slabs

    To prepare a paving slab base, use string and pegs to mark out an area approximately 5cm wider than the base of the shed. Dig out the soil, topsoil or turf down to a level of 7cm. Once you have excavated the recess, remove the string 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 4cm of dry mix. Make sure the cement-sand mix 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 you have finished laying the final stone, take a step back and look to see whether your paving stones are straight and perfectly level. If they are not, make minor adjustments with the rubber mallet and re-check. Brush the surface and remove any excess cement and sand mixture; or, if there are any gaps between the stones, add some more dry mix to plug them. If you have done a good job, the end result will be a perfectly flat, level and solid base for your timber shed.

    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 bought 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 play house, an extended area of timber decking will provide an attractive veranda area.

    As with other types of shed foundation, the ground needs to be as level as possible before you start. Choose a location away from trees, foliage and significant rocks and rubble. You should also avoid any areas where you know there are buried pipes and cables, as it is not helpful to inadvertently sever a pipe or cable when digging down.

    Start the job of laying timber decking by clearing the area. Lift turf and dig up weeds. Dig down 40-50mm. Once you have removed any excess material, check the level of the area using a spirit level and if there are any uneven bits, rake over the surface until it is flat.

    When you have a level section of ground for your timber deck, cover it with weed control membrane. This will prevent unsightly weeds from growing back under the decking area when it has been completed. Always buy good quality weed control membrane, preferably the thicker the better, so that it lasts as long as possible (cheaper membranes tend to break down after a few years and it is difficult to kill the weeds effectively when the area is covered by a deck).

    Next, add gravel on top of the weed membrane up to a depth of between 40 and 50mm. Rake it until it is level. This will provide a well-drained area upon which you can build your timber deck and assemble a shed.

    How to Assemble a Timber Deck Shed Base

    Timber decks are heavy and should always be constructed on site – it might seem like a good idea to build a deck in your garage where it’s warm and dry, but when the time comes to move the completed deck, you will be in big trouble.

    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 either side if the join using eight coach bolts.

    Deck boards should be fitted with a 3mm gap between boards to allow for drainage and normal expansion due to changes in temperature. Use a deck screw as a spacer. If the deck boards need to be joined make sure you place the join at the half way point of a joist. The decking will be stronger if joints are staggered across the deck, but for a smaller deck, this shouldn’t be an issue.

    Commercial timber decking will be pressure treated before you purchase it, so the timber is well protected against the weather. However, sawn timber ends will need to be treated with wood preservative to prevent moisture from rotting the edge of your decking.

    Solve Drainage Problems in a Timber Decking Shed Base

    Drainage can be a problem if timber decking is laid in areas of poor drainage. The timber used for decking is treated to protect it against rot, but if your garden regularly floods and the decking ends up sitting in standing water for significant periods of time, it will rot. To prevent this from being an issue if your garden is affected by poor drainage and standing water, position your decking on concrete pads.

    These are created by digging 150mm x 150mm holes that are 150mm deep at intervals of 1.2m around the perimeter of the deck. Fill the holes with concrete and level them off using a length of timber and a spirit level. When the concrete pads have dried, cover the entire area with weed membrane and gravel, leaving holes on the membrane for the concrete pads to fit.

    Before positioning the timber deck on top of the concrete pads, place pieces of damp-proof course between the pads and the deck. This will prevent water seeping up and damaging the timber.

    Safety First

    Care should always be taken when undertaking any type of DIY task. Laying a concrete base or cutting timber for a section of decking is not without its risks, so always make sure you wear appropriate safety wear and take care when using power tools.

    • Protect your eyes with goggles when cutting timber and wear a mask to prevent any inhalation of sawdust.
    • Gloves should be worn when mixing concrete to prevent skin damage.
    • Be careful when lifting heavy stone slabs.
    • Don’t lift from the waist and if necessary, get someone to help you.
    • Switch off power tools when they are not being used.
    • Don’t burn treated timber off-cuts as the smoke will be toxic. Instead thrown them in the regular waste bin.

    How Not to Prepare a Shed Base

    As we have already discussed, concrete, timber decking, a timber frame or correctly laid paving stones are all suitable foundations for a timber shed. Other, less suitable foundations include rubble, gravel, loose dirt, grass, and bare ground. It is also a bad idea to install a shed on paving stones placed on top of loose gravel – they might appear to be secure, but the ground is almost certainly going to subside over time, which will negatively affect the structure of your shed.

    Pay a Contractor to Build Your Shed Base

    There are many reasons why you might not want to spend the time building a foundation for your new shed. Digging out a foundation and laying concrete is not everyone’s idea of a fun weekend, so if you have neither the skill or interest in getting the job done, it is sensible to pay someone else to do it for you.

    You may find that the place where you bought your new shed offers a complete installation service that includes preparing a suitable foundation. If this is the case, make sure you have a suitable area for installing your shed before you buy it, or you may end up paying for an installation service you can’t use.

    If you choose to pay another contractor to prepare a shed base, get a few quotes before you hire anyone and don’t be conned into paying more than is necessary for a shed foundation. The job should take no more than a day to complete, and materials are not expensive – unless you want timber decking, which can be a bit more pricy when compared to paving stones and a bit of gravel.

    There are lots of garden shed plans available online, so if you decide to go the extra mile and construct a shed as well as prepare the foundations, look at shed plans before you measure out the base for your new shed. And once you have installed your new garden shed, why not personalize it with some paint, hanging baskets and pretty lights. Garden sheds needn’t be boring and utilitarian – with a bit of imagination they can become the focal point of your garden.


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