Are bearers/skids needed for garden room pier base?

[steve777a]

I'm building a garden room and I plan to use a pier foundation. My plan is to put the floor frame straight onto the piers, with a DPM between the floor timber and the piers.

However, from browsing the web I've seen quite a few floor structures that use bearers/skids on top of the piers, and then the floor frame is put on top of the bearers. The floor joists run perpendicular to the bearers. Are the bearers needed and what is their purpose please?

I can think of a few possible reasons:

1) For some reason the floor frame isn't designed to be that strong, so the bearers provide a strong base frame for the floor to sit on.

2) To help spread load between piers. If it is this then I suppose the answer about whether they are need will depend on the number and stability of the piers.

3) Ventilation space. The piers provide plenty of ventilation space (100mm) under the floor, so the bearers aren't need for this in this case.

4) It adds stiffness to the floor structure, like using noggins.

I'd rather not use the bearers as it adds height to the structure that I'd rather use for internal space.

Thanks,
Steve

 

[steve777a]

It has occurred to me that it is probably to do with the spans between piers/joists being too large to support flooring. By putting a separate floor frame on top of the bearers you provide a framework with smaller joist spans more suiting to support the sub-floor.