u/Business_Discount380

I'm looking to put up blinds on the attic Dormer window it's a timber frame dormer (no concrete) with insulation board and plasterboard.

I know the best way might be to put a screw straight in the timber but I'm not sure what length would be appropriate?

Most of the videos that talk about fixings for insulation boards are corefix but for concrete walls. Any other options?