# Ceiling Insulation



## Scoocher (17 Feb 2010)

Was going to be use airtight membrane (siga or isover) under the insulation on all my ceilings but then heard of these multifoil insulations (Gen-x, Aluthermo, Xfoil) that improve the overall u-value while also having the ability to provide airtightness if installed correctly (i.e. overlapping of joints and taped to the walls).

Would anyone recommed the follow@

rafter roll between 175mm joices as I need to keep my attic space, Gen-x attached to bottom of joice, counter batten the joices to leave an air gap of at least 25mm and the apply your insulated slab.

Will this work? Both to improve u-value and provide airtightness.
Any caveats associated with this type of installation.

Also what would people recommed doing in the attic to ensure a bit of warth to prevent condensation and mould growing on items stored there.


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## gar mul (20 Feb 2010)

hello  i just finished insulation on my home 3300 sq  iused tvek supro felt on roof .    2x2 batten on rafter inside give xtra dept. metac from isover 180mm between rafters 220mm on ceilings.  siga for airtightness . and  38 mm  insulated board on all ceilings and external wlls and you wont go far wrong . 1 other tip would give u  plaster all external walls in inside before u  fix plasterboards good for airtightness


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## onq (20 Feb 2010)

38mm insulated board on external walls isn't enough AFAIK.

ONQ

[broken link removed]


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## Capt. Beaky (21 Feb 2010)

Should be at least 50mm on external walls.


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## Lex Foutish (21 Feb 2010)

What's the thickest insulation you can get on plasterboard? I still can't decide whether to go that road or to insulate externally.


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## Capt. Beaky (21 Feb 2010)

Have used 75mm. This was secured onto existing timber ceiling by 5/120 screws plus penny repair washers (4mm hole). Before skimming, dab each fixing with silver zinc or other rust inhibiting paint and scrim over.


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## TripMeUp (22 Feb 2010)

gar mul said:


> hello i just finished insulation on my home 3300 sq iused tvek supro felt on roof . 2x2 batten on rafter inside give xtra dept. metac from isover 180mm between rafters 220mm on ceilings. siga for airtightness . and 38 mm insulated board on all ceilings and external wlls and you wont go far wrong . 1 other tip would give u plaster all external walls in inside before u fix plasterboards good for airtightness


 
Hey Gar Mul,

From reading the above, am I right in saying that you have 180m Metac between your rafters, 220mm (Metac or Moy Plus ??) on the flat attic part and then the Siga membrane on the underside of the rafters/joists and then the 38mm insulated slab??

I thought I had read somewhere that you couldn't have the air tight membrane between 2 layers on insulation as it may cause issues....??
Did you check this?

thanks


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