Seagrass insulation of the roof rafters

Hello everyone,

I bought a house from 1967; an extension was added in the mid-80s.

Width / length of the walkable attic approx. 10m * 7.5m

Height in the attic just under 1.8 m in the middle.

Energy efficiency class of the house: F
The energy certificate stated that the basement and top floor ceiling can be insulated as individual measures.

In the attic of the extension, I discovered some old insulation (see picture). I think it is mineral wool (yellow with a silver surface).

The original building is also somewhat insulated (something gray, see picture).

Over both areas (extension and original building), floorboards are nailed down for walkability.

I would like to use the attic for storage and use sustainable local materials. Removing the nails from the floorboards is certainly laborious, so I wanted to access the rafters.

My plan:
I would like to widen the rafters by about 11 cm with expanders and fill them with about 25 cm of seaweed.
A foil should be stapled between the roof tiles and the seaweed, and the whole thing closed with, for example, wood.

Questions:
1) Does this double insulation make sense (something unknown on the floor and seaweed in the roof)?
2) Which foil is best to use?
3) With which wood should I clad?

Best regards and thanks in advance
Morus

no, in my opinion it doesn't make sense. The old glass wool with the silver foil as a vapor barrier has to be removed and redone. The insulation of the roof can be done additionally but then not with reed grass but wood fiber or cellulose if you don't want glass or stone wool. The materials should become more vapor-permeable from inside to outside. That means the foil inside or glued OSB board, insulation, and then a wind barrier to the roof panels

no, in my opinion that doesn't make sense. The old glass wool with the silver foil as a vapor barrier needs to be removed and redone. The insulation of the roof can be done additionally but then not with reed grass but wood fiber or cellulose if you don't want glass or rock wool. The materials should always become more diffusion-open from inside to outside. That means the foil inside or glued OSB board, insulation, and then a wind barrier to the roof panels

Thank you very much for the help, why does the old insulation have to be completely removed? Then there would be space under the floorboards again for stuffing with seagrass? I rather didn't want to use wood because of the lack of resistance to fire. Best regards

Hello,

did you take the seaweed and can report?