Attic conversion - insulation, battens, etc.

Good morning,

we bought a large multi-family house in 2014 and now want to convert the roof there.
Year of construction 1987.

Since the builder passed away and his wife had hardly any plans or other experience, I cannot provide too much information.

It is a pitched roof.

What I could see is that we have a normal roof tile covering.

Below that is probably the battens/counter battens.

Now it gets exciting.

I have been told that you can either lay a foil as an underlay membrane or naturally make this out of wood "boards" since these manage moisture better.

We definitely have this wooden board nailed to the rafters of the roof.
Additionally, a grey/black/silvery foil can also be seen there… (through the gaps).

So practically rafters, wooden board, foil, battens/counter battens, roof tiles.

Currently available are 200 m²
ALUJET Topjet vapor barrier foil
blue B2 (DIN 4102) Sd-value > 100 m
+ tape, glue, electric stapler, etc.

Wood battens on the rafters for the drywall.

Drywall boards, 1200x1600x12.5mm
for the entire roof area.

Rockwool glass wool.

Underfloor heating system etc. all already there, electrical etc.

1. Point, we have practically spent almost everything and barely have any cash left.

Now my question.

1.
At what distance must I attach the wooden battens so that the drywall does not fall on my head?

2.
Is the vapor barrier/brake foil sufficient?
Do I need one at all?

We have, typical for old buildings, a huge window front – double glazed wooden windows.
One of them can be opened.

3.
How thick must the glass wool insulation be? Full filling of the rafters?

4.
Do I have to insulate again between the vapor barrier and the drywall?
My father-in-law insists on it, but I’m not so sure… the moisture should not get into the insulation material?! Then I could just leave out the brake.

5.
Do I absolutely need an airtightness test? If yes, can it be done yourself?
What do you need for it?

My father runs an emissions measurement team, maybe we have access to equipment that way.

6.
There is currently an unused ventilation system installed in this house… now I have a roughly 30 cm diameter exhaust pipe running from the floor through the roof to the outside.
On the roof, there is a small hood which is supposed to prevent rain from entering.

It doesn’t always work in heavy storms, as water runs down the pipe and then drips onto the floor.

Can I just fill it with PU foam or other waterproof filler so no water gets in there anymore?

I would rather not remove it because you can perfectly connect a complete building climate system there…

In the worst case, it just stays as it is, fortunately it is located exactly where we wanted to keep the storage space.

7. Question about laying the floor.

The attic "floor" is quite uneven.

A "subfloor" was laid there a long time ago… but not properly.

I would like to level it, but don’t know how to do it, BECAUSE a screed is out of the question.

Explanation:

We have a ceiling slab of the floor below about 30 cm lower than the stair entrance…

These 30 cm are completely filled with insulation material and above that, the wooden battens for the subfloor have been spanned crosswise.

Additionally, the floor below has another 20 cm of insulation and a "wooden ceiling".

Therefore, I absolutely cannot fill (screed)… otherwise, I would have all of that inside the insulation.

Should I now simply lay a second subfloor?!

The old one cannot be removed… it somehow seems to run under the rafters… it’s not clear how and where it was mounted.

However, we have a huge mega-thick "beam" lying on the edges of the roof on each side… I guess it lies exactly on this floor and so it was anchored like that.
This in turn is connected to the rafters and thus cannot be removed.

8. On my roof rafters, on each roof side, 2 boards each 4 meters long, 25 cm wide and 12 mm thick are screwed diagonally along the rafters. Exactly from one end up to the middle and then forming a "triangle" down the other side again.

I could of course increase the insulation by 12 mm and lay the vapor barrier foil over it, but then these would be disturbing "bumps" which will surely make the job a little more difficult.

Also, I don’t know how I should do it with the wooden profiles there… longer screws every few meters?

However, I already have the question of whether I even need these diagonals… they don’t look really stable and whether they actually support the roof is questionable, but what else should they serve for?

Who do I have to call who tells me if I really need these things?

A structural engineer??! And what does something like that cost?

So,

it would be nice if you could take away a few of my fears ^^

Thanks

Best regards.

Where is the Edit button ....

regarding 8. I can also upgrade all the rafters with small wooden blocks on this diagonal... practically my 12mm everywhere on it.. just annoying extra work

Good morning,

we bought a large apartment building in 2014 and now want to convert the roof there.
Year of construction 1987.

.

Do you have a permit for that?! Go to the architect, this will never work otherwise.

Why do we need permission for this??

The roof is practically already built ... only insulation, walls, and a better floor are missing.

Apart from that, I just want to use it for myself.

I don’t want to make any significant changes... if I put up drywall in my apartment now, I don’t have to run to the authorities either.
It wouldn't be much different on the roof... wooden profiles, insulation, drywall, fresh floor.

What happens if I don’t register it?
Our building authority is not exactly the fastest in the world
Just the business deregistration in the middle of a residential area took 1.2 years...

So again, just called the building authority, they say everything is okay. It's only about 50 m² that is to become a living space.

I only need approval for my own apartment or kitchens/bathrooms in the attic.

Otherwise, pay attention to fire protection F30.. but well, we have that anyway.
All other requirements are self-explanatory.

So now only my open questions need to be clarified.