Another outbuilding / garage floor detail question

[Moonshine]

I am putting together drawings for a posh outbuilding / garage, with a concrete slab and timber frame walls. This will be a posh outbuilding first and maybe a garage in the future.

 

My initial idea for for the floor junction detail is below, this has 100mm of celotex which maybe overkill in the floor, on a 150mm concrete slab.

 

The issue is that i want to maximize head room in the posh outbuilding, so i could either reduce the thickness of the insulation or i could bring the slab level down so the FFL is level with the outside ground, or a little step into the building. The problem is that i don't know how i would maintain the 150-160mm gap from the surrounding ground to the timber frame.

 

Also how can i minimise the cold bridging of block at the base of the timber frame?

 

[Moonshine]

Any assistance on this pls?

 

 

 

 

[JohnMo]

Would you be better having the insulation below the concrete? Wood above the insulation will give very little load bearing if you used for cars later.

 

Would you benefit from better u value for the walls as the building is being heated, your electrical bills could be huge? Consider using a layer of PIR over studs on the inside, if you tape this you could delete the vcl and improve u value by reducing the repeat thermal bridge.

 

Do you need a double skin of osb/ do you need any osb?

 

Should there be a dpc/ DPM at the bottom of the wall?