Velux Cladding/Flashing Condensation

[JohnMarsden]

Hi all,

 

I’m at the boarding stage of our loft conversion and have - with the cold weather recently - noticed that early in the morning there are a small amount of water droplets coming from between the Velux frame and opening on 1 of our 3 windows.

 

Originally thought it was a leak so pulled out my frame and reveals insulation and ripped out a bit of expanding foam I’d put between the gaps and have gradually discovered that it’s condensation forming on the underside of the cladding of the window itself. From daily observations it’s dried up by about 10AM.

 

At the moment the loft is a bit of a Swiss cheese - there are large eaves storage areas that have yet to have doors (insulated) put on them etc or be boarded, and so theres a few avenues warm air could get up into the rafters and condense on the underside of the cladding, but would the ventilation gap (50mm - I’ve 150mm rafters with 100mm PIR between them followed by 70mm PIR below rafters on the pitch) not have been sufficient to remove this moisture?

 

I am trying to figure out if that once this is all sealed, boarded and plastered it will resolve itself and this is understandable at this stage of the build given that so much air can freely circulate up to the roof space, or if something more drastic is required. The windows have thermal collars fitted as standard.
 

I have ordered a few Velux BBX vapour barriers for the windows in the hope this will address something, but would be grateful for any input. I had considered stripping off the insulation from the other 2 windows but am wondering whether this would actually aid warm air finding the cladding and lead me down the garden path.