
In some respects the trench fill foundation is similar to deep strip foundations except for the fact that the trench is deeper and requires more concrete. With the trench fill foundation the ground is dug and a trench is laid. Once the trench is in, it is then filled with concrete. The concrete should be more than five hundred millimetres deep and have a minimum depth of a hundred and fifty millimetres below ground level - some builders may recommend that it should be taken to a deeper level.
One of the good things about trench fill foundations is that they are quicker to prepare than deep strip foundations. This means that there is less disruption once the building work starts and not as much labour time will be needed. This means that if all goes according to plan then a conservatory with a trench fill foundation will be finished sooner than one that has deep strip. It is less likely that subsidence will occur in cases where there may be changes in the soil's substrata.
While it is good to know that your conservatory will be built sooner with a trench fill foundation, it may prove a stretch for your budget. Trench fill foundations require a lot more concrete than a deep strip foundation and this can be expensive. You should ask for quotes on the cost of concrete; if it is too expensive then you may have to down grade on the conservatory that you wanted.
Trench fill foundations are usually recommended if there is a high water table. It is also used where there are trees growing nearby and if the soil in the area is loose. If the builder observes that there may be ground heave then they will advise that the sides of the trench should be lined with a compressible material and mesh reinforcement.