Dave Jones Posted November 19, 2021 Share Posted November 19, 2021 only ever use a 'hybrid roof' when its designed by a firm with PI insurance for you to claim against when it goes wrong. Personally would not ever use a VCL for a traditional cold roof, newly built houses are air tight enough without stopping any moisture from being able to escape. Trickle vents wont be enough. Link to comment Share on other sites More sharing options...
Dave Jones Posted November 19, 2021 Share Posted November 19, 2021 On 17/11/2021 at 20:15, ADLIan said: Cold roofs should incorporate an AVCL to help prevent/minimise air movement and moisture vapour transfer through the system - what does get through can then removed by the ventilation above the insulation. no this is bad advice, especially for newer air tight houses. Trapping moisture in the house isnt a good plan. Link to comment Share on other sites More sharing options...
ADLIan Posted November 19, 2021 Share Posted November 19, 2021 @Dave Jones you are confusing ventilation of the whole house with ventilation of roofs. Please refer to BS 5250 (yes I’m using the 2021 version, at great expense! The information on the use AVCLs has not changed). An AVCL is required otherwise you are allowing lots of moisture vapour into the construction where it will condense on the next cold, impermeable surface above the insulation. Link to comment Share on other sites More sharing options...
Dave Jones Posted November 19, 2021 Share Posted November 19, 2021 3 minutes ago, ADLIan said: @Dave Jones you are confusing ventilation of the whole house with ventilation of roofs. Please refer to BS 5250 (yes I’m using the 2021 version, at great expense! The information on the use AVCLs has not changed). An AVCL is required otherwise you are allowing lots of moisture vapour into the construction where it will condense on the next cold, impermeable surface above the insulation. just to be clear a traditional trussed cold roof does not require nor should have a VCL. Link to comment Share on other sites More sharing options...
ADLIan Posted November 19, 2021 Share Posted November 19, 2021 Read BS 5250. I’m not wasting any more of my time on this subject Link to comment Share on other sites More sharing options...
Happy Valley Posted November 19, 2021 Share Posted November 19, 2021 1 hour ago, Dave Jones said: only ever use a 'hybrid roof' when its designed by a firm with PI insurance for you to claim against when it goes wrong. Can you elaborate on this. Why is it going to go wrong? Link to comment Share on other sites More sharing options...
Dave Jones Posted November 19, 2021 Share Posted November 19, 2021 7 hours ago, Happy Valley said: Can you elaborate on this. Why is it going to go wrong? the point being, how is it going to go right ? 1 Link to comment Share on other sites More sharing options...
ETC Posted November 19, 2021 Share Posted November 19, 2021 8 hours ago, ADLIan said: Read BS 5250. I’m not wasting any more of my time on this subject You sound like my boss. He’s forever telling us to look up the BS. Unless you are? You’re not though are you?? Link to comment Share on other sites More sharing options...
ADLIan Posted November 19, 2021 Share Posted November 19, 2021 May be……may be not???!!! Link to comment Share on other sites More sharing options...
Iceverge Posted November 19, 2021 Share Posted November 19, 2021 12 hours ago, ADLIan said: Read BS 5250. I’m not wasting any more of my time on this subject Hi @ADLIan Can you show me the part of BS5250 you're referring to please? Link to comment Share on other sites More sharing options...
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