Currently having a flat roof to pitch converson done on the third bedroom extension on my 1930's semi. Where the new hipped roof meets the old the builder has made 2 lead valleys. where the cut rosemary tiles sit above the lead there is quite a large gap, should this gap be filled with mortar. I asked the builder and he said he would if I wanted but they usually don't because the mortar can suck the water in by capillary action, is this correct. I'm also not sure if th valleys are constructed properly as, he's basically made a vee out of floorboards and layed lead on top. The pictures of valleys I've seen have a slat running up the edge of the floorboard and the lead shaped over the top of this slat the the tile sits on top.