PIR above rafters

[Dave Jones]

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.

[Dave Jones]

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.

[ADLIan]

@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.

[Dave Jones]

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.

[ADLIan]

Read BS 5250. I’m not wasting any more of my time on this subject

[Happy Valley]

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? 

[Dave Jones]

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 ?

[ETC]

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??

[ADLIan]

May be……may be not???!!!

[Iceverge]

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?