Roofing

Interstitial condensation on new flat roof?

Anonymous user 03/03/2024 - 3.36 PM

New flat roof as part of loft conversion. Flat roof area is about 4x5m. Construction is with a cold roof (architect specified warm, builder changed it to cold to maximise height), EDPM on OSB, 50mm air gap then 150mm kingspan between the joists and 25mm underneath. Vented along the length (ie 4m) Kingspan is taped on the upper surface. Wiring rungs on top of Kingspan and comes through in 6 places for surface mounted downlights (but obviously wires come though skim) Went up in summer, no leaks with really heavy rain, now it's got cold and snowed there is water coming in down wires and in the ceiling - drip drip drip. Room is currently unused, drip continues if heated or unheated. Builder has been back and looked with an endoscope, thinks it's condensation Plan is for mushroom vents x 4-6 Does this sound like a plan? Will this work? We're in NW England 17/01 -> thanks very much for all the details and advice. Builder's opinion is cold roof allows it to be lower as the insulation can sit between the rafters rather than on top. We are very height limited (only just 1.9m internally). How would you build a warm roof without raising the height of the roof please? (or using very expensive insulation options?) It's built now but not yet signed off by BC. My understanding is that cold roofs are OK in England but not in Scotland, is this correct? The vapour barrier is yes, as you say, the taped upper surface of the kingspan. Then there's the plaster skim, but obviously this has 6-7 holes in it for the the lighting wires to come through (which must also allow some vapour, as 1-2 of them have water dripping down them....) And yes, the roof is ventilated along its 4m length on both sides, 50mm, checked with an endoscope and definitely not blocked, and consistent 50mm air gap underneath deck. There's no other obstructions, end-terraced house but no others have dormers I've been up on the roof this morning with food dye in a watering can to try and rule out a leak in the EDPM/where it meets the roof!