Warm Roof - Fascia Insulation?

I

iDIY

Hi guys, I am almost ready to construct a warm flat roof on top of a 5m x 3m dense concrete block cavity wall garage/workshop. The roof joists will span the 3m length of the building spaced at 400mm centres along the 5m length of the building.

I will be using a bottom deck/vcb/125mm kingspan/top deck/grp construction but my question relates to insulating around the sides where the fascia boards are located?

if I simply attach upvc fascia to the ends and along the sides of the exposed joists then obviously warm moist air below the warm roof would condense on the back of the fasci boards wouldn’t it? So should I be installing kingspan between the joists just above the inner leaf of the walls?
 
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The cavity insulation should meet the roof insulation.

The idea of moist air condensing on fascia boards is, I would suggest, a case of reading too much of the wrong things.
 
The cavity insulation should meet the roof insulation.

The idea of moist air condensing on fascia boards is, I would suggest, a case of reading too much of the wrong things.

So the answer is a simple yes, there must be insulation between the joists to fill the gap between where the joists sit atop the walls and the bottom of the warm roof.

The idea of moist air condensing on the back of fascia boards if there is no insulation is basic physics, nothing todo with reading the wrong things.
 
The idea of moist air condensing on the back of fascia boards if there is no insulation is basic physics, nothing todo with reading the wrong things.
No it's a misinterpretation of physics.

What's the dew point of the fascia again?
 
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No it's a misinterpretation of physics.

What's the dew point of the fascia again?

The fascia doesn't have a dew point, it is the air that has a dew point, below which it then condenses. In mid summer in the uk the fascia shouldn't get cold enough on the inside or even the outside to be an issue. If however its mid winter and the temp outside has been a steady -5 then the fascia on its inner face will certainly be low enough for the warm air coming into contact with it to drop below its dew point.
 
Thanks for the science lesson. I'll try and inform the building and housing industry on this revelation.
 
Just read back over @iDIY 's posts, what an obnoxious ****! Especially to 2 of the forum members who are most able to advise and help.

I assume he is building himself, as he has scared every builder in the country away with his horrific attitude!!

Tony was right in the other thread, best the OP seeks advice for his clear anger management issues.....
 

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