Many people have been looking at sheds or summerhouses as home offices after the rise in working from home caused by the pandemic. Others have decided to make more of their garden space given that socialising outdoors is safer than seeing people inside.
Sheds are popular as garden home offices because planning permission is not normally required in order to build one. If you are planning a larger than usual construction or live in a conservation area, it is worth checking with your local planning office, however.
Whatever you need your shed for, it all starts with a good base. Shed bases should not be built on uneven ground, because this is likely to invalidate the warranty of any building products used, as well as cause damage to the building and contents.
Working out how to lay a shed base properly will ensure your shed is safe to use long term. Many sheds will last decades when correctly built, needing nothing more than coats of varnish or paint on a regular basis to protect the outer surfaces from the worst of the weather.
If you choose a more luxurious version with a glass window for natural light, getting the base right is imperative to prevent damage to the window, which could crack or break if the shed base has been built on uneven ground. It is also no use constructing a timber shed directly over soil, grass or gravel, no matter how level it is, as this will let moisture wick upwards into the timbers, rotting the walls from the ground up.
So, how to build a shed base on uneven ground? A base needs to be firm and level to prevent damage to your shed, and this will take some work. It’s not ideal to find your shed has been damaged in a storm when you use it simply for storing tools or a bicycle, so imagine how much more problematic it would be if that happened to your home office.
The easiest way to ensure your shed is constructed properly is to employ a local builder to undertake the task, but if you intend to make this a DIY project, you need to know how to build a shed base on uneven ground.
First of all, decide where the shed is going to be located. To save work, if your garden has an area of lawn or soil that is already almost flat, or there is an existing patio or terrace with flat flagstones, that is the best place to put your shed.
Otherwise, you will need to construct a base. Your shed should be placed a safe distance away from solid objects such as the garden wall or fence, mature trees with long roots or shrubs. A shed roof generally has an overhang, and space can help to prevent damage to the shed from unstable fences, walls or branches.
Overhanging branches can rub the roof felt, storms can cause trees to lose branches and fence panels to topple. In addition you will need access all round the shed for maintenance and painting or wood treatment. Of course, you should also consider practical things like walking to the shed in wet or snowy conditions, natural light, and whether you need electricity for heat and light or a water supply.
There are three ways to start your shed off well in life. You can choose a concrete base, a paving slab base or a timber frame with gravel for your shed base.
Whichever option you go for, it is worth taking the time to ensure the foundations are totally level, as shed bases built on uneven ground have a habit of disintegrating before their time. A good shed with a properly laid base can last twenty years or more. A shed with a base on uneven ground could be totally destroyed in a winter storm.
A concrete base for your shed
A concrete base for your shed will give you a permanent foundation to build on. If you’re thinking of long term use, then this is probably the best option. It is suited to any shed which will be used as a home office or workshop.
A concrete base is also very low maintenance once laid. It’s relatively simple to mark out the shape using wooden pegs and string. Add 2 inches (5.08 cm) to each length, measuring diagonally to make sure you have a right angled area with enough space for the timber lining. If you want the concrete base for your shed to be level with the surrounding land, then you should dig out the area to around 6 inches (15.24cm) for a 3 inch (7.63cm) layer of crushed hardcore sub-base and the same depth of concrete. Once you have levelled the area with a rake, remove the pegs and string.
The next step is to line the edges of the excavated area with timber. The best size to use is 6’ x 1’ (182.88cm x 30.48cm) although any planks of similar size will suffice. Check that the timber is level, using a spirit level and fix it into position with screws or nails.
Add the hardcore, (gravel, stones or crushed ballast) and compact it. Cover the hardcore with sand and compact that too. If you are not going to have a shed floor, add a damp proof membrane before pouring the concrete (5 parts ballast to 1 part cement), which should finish just above the wooden lining.
You can make the mix yourself or buy a pre-blended dry mix. Making the concrete can be done by hand or with a hired concrete mixer. If mixing by hand, add the water slowly so that the concrete does not become too sloppy.
The ideal mix for your shed base should be fairly dry. Once poured, level it using a piece of timber across the surface and add more to fill any uneven areas. Setting will take around 24 hours. If rain is forecast the area can be covered in a plastic sheet; in warmer weather, damp sacks placed over the base will help to slow the curing and prevent cracking.
How to lay a shed base on slabs
Shed bases on slabs are also a possibility. They are commonly used for greenhouses but can also be safely used for smaller sheds, especially where the shed bases are on otherwise uneven ground. Using paving slabs means that there is less work as the slabs are already levelled and cut to size.
You do not even need to use new slabs – second hand ones will do. The first step for installing a shed base on slabs is exactly the same as for the concrete base for a shed – measure the size, checking the diagonals to ensure it has right angled corners.
The excavation for the slabs only needs to be 3 inches (7.63cm) deep, with 1.5 inches (4-5cm) of that for the sand/cement base mix and the rest of it to take the slabs. The dry mix of sand/cement should be 8 parts/1 part and should be raked level as you lay it. Once that is completed you can lay the shed base on slabs on top, starting in one corner and working outwards, levelling the slabs using a spirit level and by tapping with a rubber mallet.
Any spaces can be filled using the same dry mix that you used for the base, unless you choose to cut the slabs to fit.
Laying a timber base for your shed
A pressure treated timber base is the third option for a shed base. It is inexpensive and ideal for smaller sheds, playhouses or summerhouses. It starts with a space which you can measure exactly using the peg and string method, being sure to check the diagonals are right angled corners.
The space needs to be 2 inches (5.08cm) deep and levelled to ensure an optimum fit. You can then use gravel for the shed base, filling the excavation before fitting a bearer base into the gravel. The most important thing, for safety reasons, is to ensure the base runners are fitted at right angles to the frame you intend to use.
This is to ensure the floor has enough level, flat support evenly spread throughout the length of the building. Ideally you need bearers every 2’ (60.96cm) at right angles to the joists of the shed.
Decking can be used as an alternative timber base and can also add a veranda area to the front of your corner summerhouse 8×8 or play house. To lay the decking, choose a well drained area, dig down at least 1.5 inches (4-5cm) and rake until the area is flat. Cover the bottom of the hole with a good quality weed control membrane and top up with gravel, which should be levelled before you start building your decking.
The deck needs to be constructed on site to avoid moving it once complete. The outer sub-frame should be assembled first, then the joists can be added in. The boards are best laid with a 3mm gap between each for drainage and expansion.
How to build a shed base on uneven ground, you asked? To ensure your wooden or metal shed remains structurally sound and lasts as long as possible, it is better to follow the suggestions above. Make the base level to start with and you will have a structure that lasts.