Whether you have a garden shed or a greenhouse you will need foundations to support it. What kind of foundations you need will depend on the size and type of structure you have in your garden.
Preparing the Construction Site
For any garden building you will first need to clear the construction area of roots, stones and grass so you have as flat and clean a surface as possible. Planning permission is not normally required, but it might be worth checking with the planning office if you live in a conservation area or your proposed building is likely to intrude on the neighbours’ gardens.
Paving Slabs may Suffice
Smaller garden sheds don’t need to be on as substantial a foundation as you might think. Paving slabs laid on a flat surface are perfectly adequate. It is recommended that you set down a layer of gravel on which to place your slabs to help with drainage.
If you have a larger shed to store heavier items or to regularly work in, the foundations will need to be stronger. A concrete slab, which should be at least 100mm (4 inches) thick will make an excellent base. It is worth elevating your base slightly as this will help with drainage.
It is essential for greenhouses to be built on firm, level ground. This prevents the frame from twisting, which can cause the glass panes to crack.
You can get away without a foundation at all and simply secure your greenhouse with ground anchors. You can take the added precaution of filling in the holes you have made for the anchors with concrete. It is best to use this method if you have a pre-made greenhouse with a floor; if you build your own and decide not to include a floor, you’ll have the disadvantage of controlling weeds.
As previously mentioned for smaller sheds, you can lay gravel and paving slabs and screw the base of the greenhouse into them. The good thing about slabs is the natural drainage they offer, allowing any water from the greenhouse to seep through the cracks.
Concrete Foundations for Larger Greenhouses
For larger aluminium greenhouses you are better off with a good concrete base. The area of your foundation should be bigger than the greenhouse so find out the exact measurements before you begin. You will need these measurements to calculate how deep to dig your trench as the trench needs to match the dimensions of your greenhouse.
Wooden greenhouses really do need a foundation. Wooden floorboards might have to be replaced if damp seeps into them from the soil beneath. A brick base with concrete footings is a sound, permanent option. This will take more time and effort and should be precisely constructed. If in doubt, get the professionals in.
Large Garden Buildings
Large buildings or workshops again need a concrete base. It is essential to ensure that it is absolutely level to prevent doors and windows from sticking or not opening at all. To keep the floor dry remember to raise your foundations and slope the garden surrounding your building to allow the rain to drain away.
Paving slabs are the easiest method of supporting a gazebo with a wooden floor. Place a slab under each strut and a couple in the centre, making sure they are all the same width. If your gazebo is more than fourteen feet long (or wide) it is best to place it on concrete foundations.
Not everybody has a level garden and it may be necessary to erect your gazebo on concrete footings. This can be an expensive method, but it does make it possible for you to build your gazebo where you want, despite the problems presented by the ground it sits on.
Take Stock Before You Start
Most of these foundations can be constructed easily, but do choose one that best suits your needs. Take into account your garden, the type of garden building you have in mind and the quality of the drainage. Seek professional advice if you are at all unsure.