New Room Insulation

[Dereekoo]

25mm Celotex between rafter and 50mm over top before plasterboard .
Personality would have knocked it down and rebuilt , always going to be chilly in there .

Yep double glazed window U value is around 2.5 so lots of heat to be lost through the walls

 

[GrahamLinton]

25mm Celotex between rafter and 50mm over top before plasterboard .
Personality would have knocked it down and rebuilt , always going to be chilly in there .

They would have loved it to be knocked down and had a decent extention but there's no chance on their budget.
Sorry to be dense. The rafters are 70mm deep, you mention 25mm Celotex which would leave a required air gap of 45mm but then they are putting up T&G as the roofer said putting up pb would me too wavy because of the huge drop one side to the other.
How do I put 50mm over the top of the existing 25mm as I'd have to nail each T&G board into the rafters?
Hope it isn't a stupid question.

 

[foxhole]

They would have loved it to be knocked down and had a decent extention but there's no chance on their budget.
Sorry to be dense. The rafters are 70mm deep, you mention 25mm Celotex which would leave a required air gap of 45mm but then they are putting up T&G as the roofer said putting up pb would me too wavy because of the huge drop one side to the other.
How do I put 50mm over the top of the existing 25mm as I'd have to nail each T&G board into the rafters?
Hope it isn't a stupid question.

100mm nails , t&g will be just as “wavy” as plasterboard to uneven timber .

 

[Deluks]

It's a sh*tshow. What's your part in all this? Tell them to do it properly or walk away, just throwing good money after bad.

 

[GrahamLinton]

It's a sh*tshow. What's your part in all this? Tell them to do it properly or walk away, just throwing good money after bad.

It’s my sons house I am not there a lot but the roofer has been paid now and won’t return to fix snags

 

[Deluks]

An air gap between insulation and roof deck won't be of any use unless it's vented to the outside.
If you put insulation up as stated above, you will need ventilation between each rafter, which really should be cross ventilation, a vent at each end.

I don't now how handy you are, but the longer term fix here would be to strip the roof covering, raise up the front of the roof so that it's more flat than it is now. Infill between the top of the windows and the joists, maybe a very short stud wall.
Then a stick down vapour barrier on top of the roof deck, insulate on top of the deck, new roof covering (felt/rubber/fibreglass) and flashing. It will probably need the joist depth upgrading too, although you'd probably get away with glueing and screwing 2x2 to the underside of the existing joists.

As it is, you'll probably see the roof deck starting to rot within about 5 years.
If 5 years is long enough to save up for a new extension then crack on.

 

[Deluks]

the roofer has been paid now and won’t return to fix snags

No, don't get him back!