garage floor level.

[5544]

currently building an extension which will include an integral garage. the site has multiple levels and to find a compromise has been difficult. however, building regs state that as long as i get at least 100mm drop from the utility finished floor level to the garage floor finished level then that is all that is required.
I would love to raise my garage floor to the minimum of 100mm but in doing so i would bring the floor level up to what is currently the external wall DPC. would i be creating any issues here or should i drop it about 30mm below which would be my lowest i can go.

 

[dann09]

Thing is, that the FFL of your garage depends on the in-situ DPC level and the proposed Ground Level at the garage entrance. You cannot build-in a tank of sorts, a garage FFL thats lower than the threshold.

So determine what the threshold to DPC elevation is going to be - do a full size section drawing, and include the utility room FFL. Perhaps, scan and post on here.

Remember that any in-situ driveway will determine the garage threshold level.

 

[5544]

sorry i should have made this easier to understand. i have just done the footings and now measuring up to brick up to DPC. the issue is that the driveway floor level (which i share with next door) is basically 2 inches below the existing house DPC level at the front where the garage door is going to be.
the new garage wall is on the Left hand side as you look at the house, with the drive sloping down from left to right. The existing house wall is the right hand side, In order to get height on the garage floor to avoid drainage problems i need to bring the garage floor level to within 30mm of the existing house DPC. this would also take me higher than the driveway finished level at the front of the garage.. Building control have stated that the only thing they are concerned about will be having at least 100mm from the house floor level. If i raise the FFL of the garage to near the DCP level of the existing house is it going to be an issue since it will not be exposed to the elements. The left hand side external wall of the new garage will be double skinned, with the DPC of the inner at concrete level and the outer two courses of bricks above ground level.
i cannot take the sub structure of the garage floor down any further since i am governed by drainage that is there which would not work if it was lowered further.

 

[noseall]

I would love to raise my garage floor to the minimum of 100mm but in doing so i would bring the floor level up to what is currently the external wall DPC. would i be creating any issues here or should i drop it about 30mm below which would be my lowest i can go.

Surely having a step drop of 100mm from house to garage will mean that the garage floor is 100mm below the house dpc?

What we do is actually slope the garage floor from a 100mm drop at the house-garage access door sloping to 150mm at the up and over garage door end thus bringing it in line with external ground level.

I can't quite get me head around what your external ground levels are doing.

 

[5544]

our house is a semi and shares a drive with the house to the left as you look at it. the ground slopes down from left to right, but also from the rear to the front.
the original DPC was practically at ground level when it was built in 1954, for reasons i cannot answer. i built an extension on the back so raised the outside DPC to he correct height as requested by building control.
I am now building a garage on my half of the drive to be connected to the outside wall of the house., so the ground level on the wall to be built is higher than on the house.

i intend laying a concrete slab for the garage at the same height as the extension then placing celotex and screed to get it the same level. and resulting in 150mm difference in the two levels. the problem is that the original house DPC is 150mm lower than the extension, practically at ground level at the front of the house, again why i dont know. a bad build i think.