What to consider before pour slab??

[Sunshine12]

Hi, just trying to plan ahead before pour slab. Could someone please help with the following:

1. What is the 'average' flooring depth allowed for when marking final floor level? We don't want any steps out of the bi-fold doors/utility door but have not chosen flooring yet. Kitchen likely to be engineered timber, utility tiled. I've been googling and it seems timber flooring comes in 12-22mm quite a range.
Would you leave a 15 or 20mm space after screed?

2. Is it possible to install UFH & screed in a garage which will initially be used to park car im worried about the weight of a car on the pipes? But may want to convert the garage in future so trying to be prepared now.

Thanks in advance

 

[Sunshine12]

Should have said, floor will be made up of concrete slab, 100mm celotex, vapour barrier, UFH, 50mm liquid screed. Trying to determine how much depth to leave after screed for floor finish to make sure there's no threshold at the doors