How much insulation in my bay window?

[Ferdinand]

I have 2 bay windows of which the roofs are approx 70mm thick from inside to outside, including plasterboard below and lead above.

 

How much insulation will that have? 

 

Guessing, I make it perhaps 25mm max. This was built in 2007-9 ish,

 

Cheers

 

Ferdinand

 

[ProDave]

If it was that recent then I would have hoped they would have made the roof a lot thicker and put a decent amount in. But knowing mass market builders it might not have any (as my 1930's semi didn't, until I put some there)
 

[Ferdinand]

IT is actually a self-conversion, but the measurement was inside/outside so it should be quite accurate.

 

I guess if I was making a bay window I would put 75-100mm celotex in there.

 

Ferdinand