Convert and insulate the attic

Hello,

I want to convert and insulate my attic. The following procedure is planned: There should be 2 rooms in the attic. Additionally, a shower bathroom should be added. Walls should be constructed using drywall. The knee walls should also be shortened to gain more floor space. The top floor ceiling should be clad with drywall. Boards of wood with tongue and groove (16mm) should be placed on the collar beams so that the attic is walkable to store small items there. Attic height at the ridge about 1.30m high. The attic is unheated. The ceiling to the attic should also be insulated. Also, on all roof sides including the attic with insulation between the rafters. Then a vapor barrier or vapor retarder on everything. Everything should then be clad with drywall.

My questions:

- Is a vapor retarder sufficient in the normal rooms (I was thinking of Isover climate membrane Vario KM duplex)?

- Do I need to install an additional vapor barrier in the bathroom? Do all walls + ceiling in the bathroom need to be fitted with a vapor barrier?

- Does anything special need to be considered regarding the ceiling insulation, especially the vapor retarder, because of the floor hatch?

- Do I need to use a vapor retarder with a lower Sd value for the attic? Or is it better not to insulate the attic?

The house is from the 1950s. So far no insulation. On the rafters as underlay membrane there are tar paper sheets. Rafter depth about 12cm.

Thank you very much. I look forward to many suggestions and tips.

Hello,

......

On the room side, a vapor barrier or vapor retarder is always required on all sides, depending on the usage! In the case of the attic, it depends on how it is used. For residential use, it must be treated the same as the other rooms of the attic. Otherwise, excessive insulation measures can be avoided (proportional roof and gable surfaces). In that case, the exterior roof covering (OGD) should be largely vapor-open (top layer) and the roof space should, if possible, be passively ventilated through or behind!

Best regards