There is no need to do any housework at all. After the first four years the dirt doesn't get any worse.
There are a number of variations on this quote, all attributed to Quentin Crisp: sometimes it's "some" years, sometimes it's two years, and sometimes it isn't dirt, but dust.
The thing is, he wasn't thinking long term.
On Friday we removed a small section of the granary floor so that the small set of steps up to the floor level would fit better. In order to neaten things up, we decided to put a little bit of concrete under the steps, which meant moving some of the loose sand that was sitting there. I grabbed a shovel and dug - then dug some more. The sand was actually very fine dust and there didn't seem to be an end to it, so I grabbed a broom handle and had a little prod about to find the floor level.
You can imagine my surprise when the handle went in 30cm (12 inches).
I then kept on pushing, much to the amazement of Susan and Stéphane, until I could push no more. Not because I hit the floor, but because the stick was in danger of disappearing. That is 1.3 metres (4'4") of dust.
Yes - that little black thing is the same handle.We assume it is old grain dust. It has never shown any propensity for blowing into the house so for the time being we are going to leave it there, but it will now be behind a wall. One day we may lift more floor to find out what is actually under there, but that is for a time when we are feeling brave (and have less to do).