Insulation will be an important part through out the year when living in the loft conversion. In the summer with out the right insulation will make it very hot and sticky at night and unbearable in the day time as the heat will absorb through cheap or yellow quilted insulation known as Rock wall Insulation. Rock wall though is a very good sound insulator and brilliant for in the new floor of the loft. In the winter cheap insulation will also make the loft very cold as the heat escapes and makes it very uncomfortable to use.
The worst thing is your Building Control could still pass this old insulation if the builder puts enough of it in between the joists.

So what should I use?
There are great products out there such as Kingspan insulation and Tri iso super 10 which is what I have always been around when building lofts.
Kingspan Comes in lots of different sizes and in most used size around the country is 900mm in width. silver