JamesP Posted May 14, 2018 Share Posted May 14, 2018 Ok, I have a warm roof, Pavatherm above the rafters. About to fit Tata Steel metal roof but not on OSB sheet but batten fixed vertically at intervals to support the pan. Do I have to have a 50mm ventilation cavity as its on batten not OSB which would not need a cavity for a warm roof. Is it necessary? Thanks all, Link to comment Share on other sites More sharing options...
ProDave Posted May 14, 2018 Share Posted May 14, 2018 Same as me. Warm roof, pavatex, non tenting breathable membrane, vertical counter battens, horizontal battens, box profile roof sheets. Battens then counter battens = 50mm gap anyway. 1 Link to comment Share on other sites More sharing options...
Temp Posted May 15, 2018 Share Posted May 15, 2018 I don't think you need a ventilated void under the metal roof because all of the structural woodwork (rafters) are on the warm side of the insulation. Any condensation should run harmlessly down the membrane. I would double check with the metal roof supplier just in case they want a ventilated void under the metal or other reasons? Such as preventing corrosion/rust? Link to comment Share on other sites More sharing options...
JamesP Posted May 15, 2018 Author Share Posted May 15, 2018 @Temp @ProDave Thanks for your replies. I have spoken to my BC and has said cavity is not necessary as its a warm roof. I would like a cavity so 25mm is fine, no counter battens needed. Tata want a solid deck of OSB, provide you with 40mm nails which go straight through the OSB and puncture breather membrane which does not work for me. Link to comment Share on other sites More sharing options...
jfb Posted May 15, 2018 Share Posted May 15, 2018 (edited) Are you ever going to walk on the roof? I don't think I would want to walk on a tata roof that doesn't have some sarking board beneath it. Edited May 15, 2018 by jfb Link to comment Share on other sites More sharing options...
JamesP Posted May 15, 2018 Author Share Posted May 15, 2018 No, I would always use a roof ladder for access. Less contact with the surface the better. Link to comment Share on other sites More sharing options...
Ian Posted May 15, 2018 Share Posted May 15, 2018 @JamesP the normal build up for a warm roof with an impervious roof finish like metal is to either (a) ventilate properly under the metal or (b) install a proper vapour barrier on the warm side of the construction. Link to comment Share on other sites More sharing options...
Pete Posted May 16, 2018 Share Posted May 16, 2018 I have aTata roof and this is on 18mm structural osb. DO NOT under estimate how much IMHO that you need a solid continuous support underneath the metal roof. When you are doing the ridge pieces and general finishing you will need to stand on the roof. Even a roof ladder will mark/dent your roof. I would contact Tata and talk to them. My roof make up is a warm roof with a 50mm ventilation layer and the nails have punctured the membrane but everything is fine. My/insp said we did not need a v/layer as he was not overly concerned about moisture due to us having mvhr and the level of airtightness but the timber frame manu built one in anyway. Link to comment Share on other sites More sharing options...
Alexphd1 Posted May 16, 2018 Share Posted May 16, 2018 +1 for something solid below metal. Link to comment Share on other sites More sharing options...
Triassic Posted May 16, 2018 Share Posted May 16, 2018 I’ve walked on a good number of tin roofs and they do bend and dent if your not careful. Link to comment Share on other sites More sharing options...
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