The foundation of a greenhouse plays a critical role in supporting the entire greenhouse structure. Unstable foundations can lead to uneven settling or shifting, putting additional pressure on other parts of the greenhouse. A strong and well-built foundation is essential for distributing the weight of the structure evenly. Uneven bases can lead to structural issues such as cracks in the glass, misalignment of doors and even collapse in some cases. You know the pictures people share of their greenhouse in a heap on the floor? No decent base, no decent foundation.
We recommend paved slabs as optimal bases, or concrete. We also like ring bases (either timber/sleepers, dwarf walls or concrete). While good bases can sometimes be expensive, investing in a good, solid base will save you money in the long run. It’s also really important that you know the difference between a flat base and a LEVEL base. We need a level base, greenhouses should not be installed onto a base with any fall. The above picture shows why – the base looked ‘flat’ – which it is. But look at the gap where the greenhouse would be unsupported. Imagine that with a gust of wind on it. Also, some contractors will try to build bases with a “fall” – basically a water run-off, but greenhouses need a level base – no fall, no run off. Level. Corner-to-corner level.
We like to compare it to having a huge fish tank. If you had a 6ft fish tank that was 4ft long, and you put it on an uneven, unlevel base, you would be wary of it’s sturdiness and the glass cracking. If you then went ahead and filled that fish tank with water – the weight would create pressure points on the sections not supported by the uneven base. Now, while this may be OK to a certain extent and for a certain amount of time, at some point the glass would crack and the whole structure would become unstable, would crack through the pressure and would be at risk of collapse.
Similarly, if that base had a fall (slope) on it, the water level at the top of the fish tank would slope to one side – in the same way that on a greenhouse, the water would run to one side of the gutters (front or back), which is OK if it slopes to the back and that’s where your water butts are – but not as helpful if it collects at the back and your water butts are at the front.
Any base should extend the perimeter of your greenhouse. Please remember that a greenhouse will always be bigger than advertised, by a few inches. It’s important that you follow base plans provided by the supplier of the greenhouse. For example – a 6×8 greenhouse will usually be around 6’3″ x 8’5″.
Paving slabs must be laid level and flat. Brick or block perimeter plinths must be laid on suitable footings to ensure it is level, square and exactly to the correct greenhouse size (especially given the above point). Soil bases must be level and compacted (not freshly dug).
If you have any queries or questions, or you are considering buying a greenhouse and need advice, just send us a message or give us a call, we don’t mind advising.