Shed roof white mould on air gap side of a cold deck roof

[JohnLeeWall]

I had an issue while I had some of the insulation up it wasn't all sealed in for a week and caused condensation to form on decking, dried this off as best as I could and then sealed the pir foam (50mm) in place, foamed all gaps and taped it. Now move on around 2 weeks I decided to take one panel back out to check the roof is ok and bam had all white mold growing on roof deck in the air void! yet to touch its dry so I am at a loss and I can feel the air blowing up the void against my face so there is air flow. What can I do about this? would I need to pull all foam back out and treat all the wood then put it all back in or is there another option?

Its a block shed with a low slope flat roof, no leaks but has a small parapet wall at rear so the roof buts up to this but I have gaps in the wood allowing cross air flow and some holes allowing cross flow with a 300mm vented sofit at the front and a 70mm vent to side allowing air in also.

 

[^woody^]

Mould is not normally white, but salts from water drying off is. Be sure which one you have

Generally, if there is a cold surface of the roof, then any air void below it (and above insulation) should be ventilated side to side. The alternative is to insulate tight up to the roof deck with no air gaps at all.

And if there is a gap, just because you feel air moving does not mean it is cross ventilated, it may well be just air currents caused when you remove a panel. Cross ventilation is normally a direct path from one side of the building to the opposite other side with equal venting at each side. It is a different concept to just ventilation by drilling holes and assuming air will flow adequately through holes.

 

[JohnLeeWall]

It is a white spot like mold growing down from wood in patches, some slightly turning green. The air was definitely wind blowing up as it was constant but I guess in this situation it would bounce off the rear wall and not sure if go back out or not really.

Does the hybrid method work ok of putting the insulation right up to the roof deck? as some people seem to not like the idea as they say the wood can sweat but surely that can be the case with a warm deck roof also as to me its just an upside down version of that.

I am thinking of adding those small circular wall weep vents to rear just to allow some air to vent out at the rear as it hits the back wall (if still as a cold deck).