no back felt on slate

[gudge]

there is no back felt on my slate roof ,does anyone know if a foil insulation would act as a secondary waterproof layer,but also be breathable if stapled to the rafters?? or is stopping draughts, insulating and being ready for a slate moving too much to ask from foil coated bubble wrap?

 

[noseall]

a secondary waterproof layer is there to collect and deflect any water, that gets past the tiles, out into the gutter. this can only be successful if that waterproof layer is fixed to the topside of the rafters.

any membrane fixed to the underside of the rafters, will collect water and deflect it into the cavity or into an upstairs room.

 

[gudge]

should have known it wouldnt be that easy,it never is ,
thanks for the reply .