Attic Insulation - Fibreglass wool and polythene sheet

[Steg G]

I recently had my attic converted to be used as an office. I had it floored and plasterboarded. 100mm kingspan was used with 50 mm air gap on the angled part of roof but fibreglass with a polythene sheet was used for the verticle under purlin parts. Recently i have noticed some of the fibreglass is damp at bottom and polythene sheet is slightly damp. There is no leaks in the roof. Is this normal? Should i change out the fibreglass for more kingspan? Or should a VPL be used instead of polythene sheet?
Any info would be great.

 

[conny]

Just a diy'er and don't know much about modern insulation methods but I do know polythene sheeting will condense moist warm air on it's surface.
Moist warm air can come from a variety of sources, (e.g. damp clothes drying, tumble dryers, kettle etc but also simply from someones breath), so I don't understand all these reasons for using barriers. We simply used to install insulation, be it fibreglass matting, blocks, granules etc and there never seemed to be these problems people complain about these days.

 

[BlueLoo]

I don't understand all these reasons for using barriers

Air leakage=heat loss.
Modern building standards are becoming obsessed with air tightness to reduce or eliminate air changes in a building.
Unless the building is designed from scratch to control air tightness correctly, it seems to create all manner of issues (like this one).

The Heat pump era is going to cause chaos.

I agree with your other comments.

 

[conny]

My FIL had his bungalow re-built after subsidence and they did an 'air test' before it was passed off by the BC.
Apparently they went as far as sealing off the cable conduits buried in the walls to prevent any unnecessary 'leaks'. So you take away all the leaks and actually prevent air flow to the best of your ability to heat the house as cheaply as possible. In the meantime the house owner/occupier has to start contending with damp and mould because of lack of natural ventilation.
Who thinks these ideas up, and more importantly, what idiots agree with their hypothesis as being the best way to build?