Interior finishing attic new construction

Good day dear forum members.

We are facing a decision, and I urgently need help.

- It is a new build.
- We do not have a basement.
- The heating unit is supposed to be located in the attic (according to the plan).
- The total area in the attic is 60 sqm (10m * 6m). The stair area is included here.
- Gable roof, minimum height about 50 cm and maximum height (in the middle) about 2.50 m.

I plan:

- One half (about 24 sqm), where the heating unit will be located, to also be used as a storage room.
- The other half (about 32 sqm) is to be used as living space about 3 years later.

The construction company makes the following offers for the attic expansion:

Option 1:

Over the entire area (60 sqm minus stair area):

- Underfloor heating
- Floating screed
- Interior plaster gypsum, quality Q2

Cost: €5700

Note: The partition wall including door would still have to be made separately, is not included in this cost. Will probably cost around €1000 extra (?).

Option 2:

- Expansion only in the habitable part of the room (about 32 sqm)

- Underfloor heating
- Floating screed
- Interior plaster gypsum, quality Q2
- AND: Wall including door

Cost: €5800

Note: Could there possibly be problems with mold later in the storage area (due to missing underfloor heating)?

Option 3:

- Can all this be ordered cheaper?
- Are there advantages/disadvantages of this option?

I am grateful for your quick answers! Please as detailed as possible. I want to understand exactly why I should decide for one and not for the other.

Thank you very much!

No. Mold does not arise from cold, but from lack of air and water. An unheated cold attic, but still ventilated through the roof tiles, yet dry, will not develop mold. Grandma and Grandpa used to dry laundry in such attics. Therefore, I consider the option with the partition wall to be more suitable for your plans. There will then be a warm room that can be inhabited later, and a cold room that is purely for storage. And whatever is stored there will stay dry; whether it is cold in winter does not matter at all to the suitcase, the leftover tiles, the Christmas decorations, or the folding chairs for large guests. Karsten

What storage options do you have on the ground floor?

Regards, Yvonne