Screw foundations are being used by several garden room companies. They are overcoming tricky site conditions and uneven ground which speeds up the construction process no end.
As you can see the screw piles are really just giant screws with the same sort of thread that you will find on a wood screw. This thread cuts into the ground and creates a firm grip.
— eDEN Garden Rooms (@edengardenroom) March 27, 2017
These foundations are driven in with a special tool, and one of their great benefits is that they can be removed with the same tool, cleanly from the site should you need to remove the building in the future.
Screw foundations like this can easily overcome uneven ground. If you use a laser level, you can set your level line and drive in a pile to just the right height.
As you can see the timber and insulation floor frame sits on top of the level piles.
The grass under the building will die away once the light is excluded as the floor is put in place. Some garden room designers would lay a weed suppression membrane before fitting the floor frame, but this just has the same end effect of excluding the light and killing the grass.
Another benefit of a screw pile foundation system is that there is little disruption to the site, so the area around your garden room will look good from day one.