Draughtproofing Tops of Stone Walls Underneath Roof

[tiz]

My house has solid sandstone rubble-filled walls. Some of the gable and internal gable walls stop a bit short of the breathable roof underlay. There is a rough gap (which is stepped due to the roof incline) between the tops of the walls and the roof underlay.

Should I seal these gaps to stop air flow behind the PU insulation boards that will line the walls? If so, does anyone have any rodent-proof fillings?

Or should I retain the air flow to help remove any condensation and seal the gap between the tops of the PU insulation boards and the walls

 

[JohnD]

Have you got ceilings, and are they below the level of the gaps?

 

[tiz]

Some are above the ceilings and some are below.

 

[JohnD]

Above the ceiling you want plenty of ventilation, so don't seal.

Below the ceiling you want the (insulated) inside wall to seal against the ceiling to prevent loss of heat and moist air from the living space.