Insulating Extension Rafters

[RichieH77]

Hi all,
I have a extension with a sloping roof.

The extension is totally open so there is no other options for insulation with it.

From what I can see the roof consists of tiles, with a few mm gap then felt a few more mm gap and then some board and then the Rafters.

Can I just plass the glass wool in between the Rafters and then board over it?

Any help greatly received

 

[Alastairreid]

100mm insulation between the rafters with 150mm crossbonded to give you your optimum 250mm.

 

[RichieH77]

Am I right in thinking the air circulation is most important between tile and felt?

I've read about condensation issues which is the main reason I haven't done this yet...

 

[Deluks]

How many mm are we talking about for these gaps. What is the board that you describe on top of the rafters?

Glass fibre or any other woolly type insulation is not the best product here. Use celotex/kingspan type boards. You'll be look at probably a min. of 130mm total insulation between and under the joist.

//www.diynot.com/forums/viewtopic.php?t=190998

Ventilation is important between the insulation and felt, unless you are using a breathable membrane. Also important to provide a vapour barrier under the plasterboard. Either tape the inso boards with silver tape, sheet of poly of use foil backed plasterboard.

 

[Alastairreid]

oops misread the post ........deluks method is the way to go.

 

[RichieH77]

Thanks for the advise guys..

As theres is a gap between felt and tile and board and tile, I think there is enough gap.

I just need to measure at a few spots to ensure that the felt isn't lying on the boards elsewhere in the roof, I guess.