Concrete Slab Levelling

[thinkwallet]

I've had a 5m x 4m (6") concrete slab laid as a base for a log cabin (kit).

The base has a 20mm belly/dip front to back in the middle of the 5m run.

I think this might cause me problems with the build and windows/doors and weather tightness between the interlocking logs. Cabin is built straight off the concrete on 70 x 70mm treated wood bearers, internal floor the same.
Maybe it's not that bad a dip over 5m, I'm not sure.

What do you think? What are my options if I need to level it?

Thanks in advance, Neil.

 

[noseall]

Wood can be planed or packed if needs be.

 

[wotan]

As Nosesall says wood can be planed or packed up.
20mm dip in 5 metres is not a great amount, i would be more concerned if it was 20mm high in the centre, the building would then 'hog'
Being low in the centre it should self tighten, a few well placed packing strips should sort it out.

Wotan

 

[thinkwallet]

Thanks, I'll pack it level.

There is something else worrying me; The cabin will be 5 x 4m dead, but the
base is 5.2 x 4.2. It was dug into a slope (2' 6" to nothing) and only shuttered on the low side which sits out of the ground 6".

I've dug a 5 inch drainage channel all around the base, and built a berlin wall (outside the drainage channel) on the high sides to retain the soil.

What I'm worried about is that water will sit on the 100mm concrete lip and run under the base. Also, concrete was not laid on DPM as it sits on 5 piles.
Can I put DPM inside on the concrete under the floor? Should I lay the wooden foundation bearers on DPC?

Thanks, Neil.