The structure being very light (the weight on the ground is of the order of 150 to 250 kg per m² according to the size of the greenhouse), in most cases, the greenhouses do not require foundations. The only imperatives: a flat and level ground, a gravel bed under the basement wall to avoid prolonged wet contact and a solid fixation on the ground.
More complex foundations are not necessary unless other important factors come into play, such as very wet or floodable terrain.
>> The ground on which the greenhouse will be planted must be flat and level. If the ground has been excavated recently, it must be compacted so that hollows are not created under the basement walls. A gap of 5 cm is tolerated.
For domes of 10m and 12.5m in diameter, it is imperative that the leveling be done to the backhoe to compact, level and level the entire surface of the greenhouse.
BED OF GRAVEL
>> A bed of gravel about ten centimeters high should be placed under the basement walls to drain water that could stagnate under the wall. The dome then rests on a circular ring of gravel. Gravel 15/20 is satisfactory. The gravel bed and also useful for catching a small drop of the ground.
It is also not necessary to dig a trench to bury the gravel. This can be useful on very wet and loose ground.
>> The dome is anchored to the ground by means of metal rods (reinforcing bars) driven into each section of the base (2 rods per section). The length of the stems varies from 70 cm to 1m depending on the hardness of the ground.
Note also that for domes up to 7.9m in diameter, the water tank attached to the basement wall, contributes by its weight to this anchoring to the ground. The installation of interior planters on the periphery of the dome brings the same type of contribution.
>> If termites are present in the area it is necessary to make a hard foundation to create a barrier and protect against insects.
OTHER FOUNDATION OPTIONS
• Intermediate cost
>> The foundations consist of cement pillars directly above each corner of the base (15 or 20 sides), the sections of the basement wall are fixed on these pillars. It is an excellent type of foundation for very loose and very wet soils.
• Higher cost
>> Pour a circular ring with reinforced concrete. The basement will be fixed on the foundations.
A diagram is available on request.