Difficult to insulate

[diyrealnovice]

I have a separate roof space on the back of my house with only limited access (a hole the size of a dinner plate). There is no insulation at present and I was considering using a loose-fill material to do the job. Please can anybody offer any advice, and advise if it is something I should be leaving to the professionals?
Also, my main loft is insulated and boarded and I have polythene attached to the rafters forming a barrier beneath the tiles and felt. Is there any reason for this, and if the loft is well ventilated is there any reason why I should not take it down?
Thank you.

 

[masona]

Also, my main loft is insulated and boarded and I have polythene attached to the rafters forming a barrier beneath the tiles and felt. Is there any reason for this, and if the loft is well ventilated is there any reason why I should not take it down?
Thank you.

No reason at all, it's just reduce the heating bills and feel warmer. The only thing I can think of is that you may not have any roofing felts so the polythene is to stop the draught coming through the tiles. I know you've mention roofing felt but can you see it?

 

[diyrealnovice]

Yes, I can actually see the felt. The polythene has now started to come away from the rafters and I just want to tidy it up, if possible.