Insulation in a 1960s flat roof - any guesses?

[lineweight]

I'm trying to make an estimate of the U-value of an existing flat roof, constructed in 1963.

 

On the original architects' drawings, it's noted as "Briggs Patent Roofing" which I think just means a layered felt system.

This is laid onto "1/2 inch insulating board" with no further info given.

 

Does anyone have any guess as to what this 25mm(!) insulating board is most likely to have been, given the construction date? Some kind of celulose/wood fibre board?

 

 

[markc]

It could be asbestos! Often referred to as insulation board.

[lineweight]

1 hour ago, markc said:

It could be asbestos! Often referred to as insulation board.

 

yes... had wondered about that.