Loft insulation - Knee wall

[hector8]

Hello

I have just insulated my roof space with Earthwool 200mm leaving a gap at the ends for air flow

Now I am planning on insulating the side attic walls. Currently there is insulation between the joints and on the floor area, which is boarded over also. I am going to roll out more earthwool on the floor but only after I insulate the walls more.

My question is... is it possible to use foam board to cover up the entire wall and seal the joints or would the fibre glass sweat and create water damage??

Other opinions and options are recommended as I am new to this. We have noticed a difference already since the roof space was done 3 days ago. Thanks

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• hector8
• 15 Jan 2014
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• 15 Jan 2014
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• hector8
• 15 Jan 2014
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• hector8
• 15 Jan 2014
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[tony1851]

It might be better to fix the board on the room side, and then plasterboard over.
The boards have a foil finish which can act as a vapour barrier. If you put them on the cold side of the existing fibreglass, there is a chance that vapour passing through the fibreglass will condense on the cold side of the fibreglass. This will reduce its insulation value and could also cause rot problems.

 

[hector8]

Thanks for your advice. Unfortunately our bedroom has slide wardrobes and built in units which we couldnt / wouldnt want to move and alter.

What if I took out the yellow glass fibre and replace with foam board, would it be better??

 

[tony1851]

What if I took out the yellow glass fibre and replace with foam board, would it be better??

Yes, inch-for-inch, Kingspan and the other foam boards are getting on for twice as thermally efficient as fibreglass.

 

[hector8]

...and then seal all the gaps?

Then roll out the earth wool on the floor like I did in the roofspace