The method of building the foundation for our greenhouse has proved to be a bit more demanding than perhaps some others – hopefully the final outcome will be worth the extra labour. The tricky part is casting concrete into long pipes, that go down into 80 cm depth – i.e. beneath the soil frost line. These concrete pipes, or pillars, need to be cast so that the the steel plinth (base) that will provide the basis for the actual greenhouse will be exactly square shaped in horizontal X & Y directions, while simultaneously also exactly at right even level (Z) so that there will be no tensions into the glasses of the finished greenhouse. The actual freezing protection will be provided by several layers of gravel and sand, separated by filter fabric layers, plus a couple of layers of Finnfoam (extruded polystyrene foam – XPS – thermal insulation). The tricky part is that those pipes I mentioned need to go through all of those other layers, and they need to be made and fixed in pretty much their correct, final positions first, before any other elements of this foundation have yet been built. From the photos underneath you might get an idea how our ambitions have met with the reality so far.
Oh, and did I forget to mention that there of course need to be also underground drain pipes, so that all rain water will not turn that big hole in the clay earth into a swimming pool? And that those pipes need to be installed at the right angle of bank.