Garage about 30 cm deeper than the house, but is it possible to add it later?

Hello everyone,
we are planning to build a single-family house in Hesse. Currently, there is no money for the garage. I plan to build the garage later, approximately 5.5m x 7.5m x 2.65m. It should be a large garage for 1 car and bicycles, etc., and built directly on the neighbor’s boundary. The garage should not be connected to the house.

The building permit or notification for the garage should also only be submitted after a few years. So the building permit for the house will be without the garage.

The problem is that the street slopes along the front of the house, and therefore the top edge of the street is below the backwater level. The architect recommended building the house about 30 cm above the top edge of the street, so we would be above the backwater level. We would have to fill in, but I have come to terms with that.

But if the garage were to be built at the same height as the house, the maximum wall height including the roof at the neighbor’s boundary would only be about 2.45m. I think that is too little for the garage.
If the neighbor does not agree that I can build about 20cm to 30cm higher, I would have to place the garage about 30 cm lower than the house.

Is that easily possible later on?

The house will be built on a foundation slab. The area where the garage is to be located later should also already be compacted so that it can be used for the construction trailer and later as a parking space.
Can the garage foundation be built afterwards as close as possible to the house and 30 cm lower? As far as I understand, about 30 cm would have to be excavated at the house base. That would be the variant with a garage on a foundation slab. Then the foundation slab of the house would be exposed on the side. That is what worries me.

I imagine the variant with a garage on a strip foundation directly adjacent to the house, where even deeper excavation is necessary, to be even more problematic.

Has anyone already done this and can report?
I am slowly regretting these planned later works, but I have to get through them now.
If everything does not work out, I will put up a carport.

I have added the picture from the street side.

Thank you

There is also the option to plan the garage on the property boundary with a sloped or gable roof, if the local building regulations allow it.

In times of increasing heavy rainfall, I would never plan a slope TOWARDS the garage.

Having it done later will end up costing twice as much for the machines. It is better to do the excavation work in one go. If necessary, finance the part later; the money will be missing anyway.

I would have the strip foundation of the garage – and possibly the garage wall towards the house – built right away, omit the floor slab and instead (later) pave the interior with brick pavers on gravel and a sub-base. Many people in our area have done this, and it has the great advantage that the runoff from the wet car soaks away downward without any problem, whereas with a floor slab and tiles, I always have to carefully use the squeegee….

Can the strip foundation then be built directly next to the house foundation with a few centimeters of distance? The strip foundation would then run along the side of the house, right?

The garage is not to be connected to the house.

Taking into account the note

In times of increasing heavy rainfall, I would never plan a slope TO the garage.

I basically read this as the freedom to have the finished floor heights vary freely.

Hello, our property looks similar. How did it work out now? How much did you fill up? Did everything go smoothly? We also need to fill up, do you have a good tip for us? Best regards