The short answer to this is none. The longer answer is well, slightly longer.
First of all though what type of temporary building are we talking about? If a building can be hired and easily removed and transported then it can be classed as temporary. Cabin type structures used for offices and school classrooms fall into this category along with event structures and some industrial steel buildings.
However for the purpose of this article we are looking at aluminium framed industrial temporary buildings typically used for short or long-term storage, warehousing and other operational on-site activity. And, the clue to the question is in the title; aluminium.
Buildings engineered with an aluminium frame as opposed to a steel frame are much lighter. So, it stands to reason they will need less load bearing than a steel building. Because of this they typically need no foundations at all and can be built directly onto existing hard standing by anchoring the frame into the ground. To ensure the temporary building will remain in place uplift tests are carried out to make sure it can withstand the maximum uplift force.
So when would a temporary building need foundations?
One obvious answer is if the ground is grass and some kind of concrete slab would need to be laid. Other than that it’s generally down to what the building is being used for and individual preference.
Although temporary buildings can easily be installed on unlevel ground sometimes it helps to have it levelled out beforehand. Using large machinery or a workshop environment where staff are working would both benefit from a level floor. Alternatively you might be buying temporary building and want a level floor to accommodate the long-term use.
Generally speaking though this type of temporary building doesn’t need any foundations or serious ground prep. And, it’s this factor that gives them their crowning glory; speed. In an emergency an aluminium temporary building can be installed in a week. From initial enquiry that is.
So, if it’s a case of capitalising on a new order or unforeseen growth you can do without the cost, hassle and delay of foundations. And, when you no longer need the building the area can easily go back to its original or new use straight away.