My bathroom is above an unheated storage area accessed from outside, presumably originally a coal shed. The bathroom has been rather cold and drafty during the winter, so I've pulled down the plasterboard ceiling in the shed and fitted 100mm Celotex between the floor joists.
Between the outermost joist and the external (cavity) wall is an annoyingly small gap, around 40mm wide (see attached photo). I've tried and failed to friction fit small blocks of Celotex due to the uneven wall, and can't accurately hold them in place to fit with a foam gun.
Should I persist with fitting Celotex somehow or would just using gun foam for the whole gap be appropriate? The gap runs vertically to the underside of the bathroom floorboards.
Between the outermost joist and the external (cavity) wall is an annoyingly small gap, around 40mm wide (see attached photo). I've tried and failed to friction fit small blocks of Celotex due to the uneven wall, and can't accurately hold them in place to fit with a foam gun.
Should I persist with fitting Celotex somehow or would just using gun foam for the whole gap be appropriate? The gap runs vertically to the underside of the bathroom floorboards.