mixing cavity wall and external insulation?

12 Oct 2012
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United Kingdom

Quick query, we have a 1920 solid brick bungalow that has had a large extension added in the 50s (block work with 50mm cavity).

A lot of the pebble dash render is in bad shape so over the summer we are hoping to strip the dash and fit EWI with new render.

Question is, is it ok to have the cavity filled now then fit the EWI later? I assume to cavity must be filled/sealed to prevent air moving in the cavity?

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As i understand your post, you want to install both cavity insulation and an external insulation system on the extension. Why both?

"to prevent air moving in the cavity", what do you mean?

Has anyone looked inside the cavity?
Thanks for the reply.

1/3 of the house is cavity wall (LH gable, kitchen, Rec1), the other 2/3 is 9" solid red brick.

I need to insulate the place and as the render is bad, im going with external insulation. To avoid a large "step" in the render outside i want to insulate the cavity wall externally at the same time im doing the solid walls.

How i see it, any air movment within the cavity renders the EWI useless as it will be carrying away heat. So to make best use of EWI with a cavity wall, any air movement within the cavity must be stopped? Easiest way i see of doing that is to get cavity insulation blown in.

Does that sound right?

Cavity has not been insulated, done extensive work on the place and not found any evidence of insulation :(

cheers Neil
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Why not call Celotex or Kingspan tech advice line and discuss your insulation proposition?

If you come back on here then maybe go to the plasterers forum for further advice?

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