The guidance is (as always) a bit fluffy. I have uncovered for a client, missing putty pads on MF/PB walls that form a 30min escape corridor. This is a no brainer - they need putting in. But the investigative report shows no putty pads where boxes are on external walls and party walls that are shown as 60min - these walls are 12.5 (grey) PB on dabs on 100mm concrete block. FYI the fire line of escape route goes through ceiling void to concrete block and beam floor. My thoughts are there is low risk of spread of flame or smoke in void between PB and blockwork as no fuel (assuming solid line of dot/dab along parameters.
