Roof insulation

[Penelopejean]

Roof insulation in new extension........ We are currently having a single storey extension built and I'm concerned that they haven't put in enough roof insulation even though the building control have "inspected". It is a partially pitched, partially flat leaded roof. What would be the current building regulation thickness of blanket fibre for this type of extension please?
Also, how can the inspector see inside the roof after the plasterboard is put up?

 

[freddiemercurystwin]

Whats the roof make-up, what make's the insulation and how thick is it?

 

[noseall]

250mm quilt on pitched roof ceilings.

90mm cellotex on flat roofs.

 

[Penelopejean]

Thanks to both replies.

The pitched roof part is concrete tiles on timber rafters and on the flat section it is lead covered on timber joists. Inside it is the normal flat(not pitched) ceiling so has a inaccessible loft. Hope that's what you need.
My builder says the standard thickness of the insulation should be 200mm but having done a bit of research it seems that, (and you've confirmed it)it should be 250mm or over.
At the moment there is a tiny accessible space where you can poke your head thro' into the roof space and I can see the ceiling joists which if it were 250mm or even 200mm thk it wouldn't be possible would it? Not sure of the depth of the joists but the width of the room is 2.3m if that helps. There are also areas where you can see the ceiling plasterboard too.

Thanks

(PS This extension of approx 15sq m is costing £35000 +VAT so am anxious that we are getting the job done to current energy regulations. I also don't want a cold downdraught down my neck when sitting at my computer!)