Overspill into flat roofs

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White wool overflowing under flat roof
I managed to get my endoscope under the flat roof and found overspill of insulation which is visible in the distance int he photo.
This indicates that the cavity isn't closed at the top which is a requirement of cavity wall insulation though not much is mentioned in CIGA's guides about how you would inspect the top of a flat roof.
It makes me worried that the other flat roofs segments of the house are filled with this crap as well.

I have already established that the installers were incompetent and didn't check the wall on the gable end of the pitched roof as it overflowed into the attic but this was much harder to spot.

Overflowing CWI into a flat roof space can cause problems. Apart from forming patchy insulation which can lead to cold areas, in this case it fills the whole height of roof space between the joist and blocks of ventilation.
impedes ventilation and stops areas of timbers from shedding moisture adequately which leads to rot.
The other problem is that depending on how the walls are arranged it may overflow right up to the fascia board on the external wall where it is far more likely to get wet and as demonstrated, this white wool wicks water like cotton wool.

 Some low resolution thermal images looking up at the ceiling concurs with the limited visual inspection and gives an idea of the extent of the insulation overflow which at one point covers half the roof. The temperature difference is almost 2 degrees - so it certainly works unintentionally as patchy roof insulation.

Looking up a the inner corner of the flat roof ceiling 

Ceiling above corner window showing part of a big patch of insulation overspill.

If you are going to have insulation in flat roof the building regulations recommend a 'warm deck' which involves building insulation on top of the existing flat boards on the roof in a similar way to external insulation panels for walls.
As I understand it, you strip the roof down to the plywood/OSB, put a vapour barrier then 120ml or so insulation boards, then screw down another layer of plywood and apply the roof covering e.g felt, rubber or fibreglass as usual.
This arrangement allows the sub roof space to ventilate, and avoids a cold ceiling surface in the room.

An alternative 'cold deck' is permitted which involves  opening the roof up and placing insulation between the joists but there must also be a 50ml gap between the insulation and the roof substrate. 

Blown insulation in the roof-space wether intentional or accidental is not acceptable.




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