PIR insulation between battens advice...

Discussion in 'Builders' Talk' started by Adam182, Oct 6, 2017.

  1. Adam182

    Adam182 New Member

    Hi everyone, currently got an exterior cavity wall battened out with 2x2, filling in between the battens with 45mm celotex, just wondered if I should fill behind the celotex with something (silicone/foam?) before I push it between the battens.

    As the batten is roughly 50mm theres a give or take gap of around 0 - 5mm behind in certain areas if I leave the celotex flush.

    Alternatively I can push the celotex right back with will leave the gap at the front which would be directly behind the Plasterboard.


    Thanks any feedback is much appreciated.
  2. Bob Rathbone

    Bob Rathbone Screwfix Select

    I would advise a breathable on way permeable barrier is placed between the wall and the frame, to allow moisture to travel outwards but not inwards. Fit the celotex and then fit a PVC vapour barrier over before plaster boarding.
  3. Jord86

    Jord86 Screwfix Select

    Keep the celotex flush with the internal side of the 2x2 and as Bob says, staple a vapour barrier over the lot or use foilback plasterboard to cover, as the foil also acts as your vapour barrier. I would also dot and dab insulated plasterboard in the reveals of your window, as that will be a cold spot unfortunately.
  4. Adam182

    Adam182 New Member

    Thanks for the feedback guys very much appreciated, will foil taping across all the celotex joints/battens suffice as a vapour barrier instead? In the corner will be a quadrant shower and I plan to use Hardie backer in that area.

    Also thanks for the heads up on the window reveals, I'll be using insulated pb on all the other external walls in the house so I'll definitely have some left over for this detail.
  5. Adam, that is existing studwork - not stuff you have fitted?

    What I would personally do - and what I've done in a single-skinned garage to make it a habitable room - is to stuff in between these studs with Jablite which is a cheap expanded-polystyrene insulation.

    (First, I would get a can of Everbuild Lumberjack wood preserver and thoroughly soak these timbers using a sprayer.)

    You can get Jablite in various thicknesses so could build up the required depth in layers or as one. It is partially springy too so chances are you could end up with it nicely flush or fractionally above stud surface, but be able to compress it in.

    It is dead easy to cut - use snap-bladed craft knife, and has springy edges so can be squished in between the studs leaving no gaps; Celotex, on the other hand, would need to be cut perfectly to fit, or else have a bead of exp foam run down any gaps.

    Then I'd overboard with insulated plasterboard at whatever thickness you can afford to lose space over, but I wouldn't bother going more than 40mm thick.

    (My garage has 25mm Jablite and 35mm insul p'board - it's cosy.)

    If you don't do this, then the insulation value of parts of that wall will be whatever is provided by the timber studs only - along with the nails/screws that pass through them in to the wall. I would personally not be happy with that - I would want an even over-boarding of insulation over it all.

    If you are having a shower or bath in there, the plasterboard stuck to these timbers will have nails or screws virtually touching the backs of them, screws which are going in to that wall. Do not be surprised if you find condensation forming as small round spots on that wall.

    That's a risk I would personally not take.
    Adam182 likes this.
  6. Adam182

    Adam182 New Member

  7. No prob - it'll be fine.

    I have this 'thing' about having an even level of insulation, and not risking cold spots.

    Ask Kools... :rolleyes:
    Adam182 likes this.
  8. Adam182

    Adam182 New Member

    Thanks for the feedback,

    In an ideal world I would have gone your route of having an even level of insulation that sounds great. Taking this house renovation on DIY style I have had alot of different methods suggested and I opted for the one I felt most comfortable with when I started, I'm pretty happy with it so far im trying to look at it now that atleast some areas of the wall bieng covered with insulation are better than none at all as it were before :).

    As insulated PB is off the menu in this case would you suggest foilbacked, MR or standard PB? some people have suggested normal PB is ok for areas outside of the shower quadrant?


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