Which acoustic insulation over PIR?

Discussion in 'Builders' Talk' started by new666uk, Jan 9, 2022.

  1. new666uk

    new666uk New Member


    We're building a garden office and the frame is mostly 3x2 which I'm most of the way through insulating with 75mm PIR. The roof and floor are 100mm PIR insulated.

    Is there a simple way to add acoustic insulation over the PIR on the walls before installing plasterboard? Just something to stop sound booming and cut out some external noise, doesn't need to be a studio.

    I feel like I'll have to fit battons over the 3x2 studs to create something I can void fill and still fix plasterboard too but have I missed an easier alternative?

  2. Jimbo

    Jimbo Screwfix Select

    Use 50mm rock wool acoustic slab between battens as you suggest. You might consider acoustic plaster board too.
    ElecCEng likes this.
  3. Jimbo

    Jimbo Screwfix Select

    Also, what is the construction of the walls?
  4. new666uk

    new666uk New Member

    Thanks @Jimbo

    The walls are 15mm cladding on a 3x2 frame. That's all filled with PIR so it sounds like I need to add spacer battons to that which will hold the Rock wool and provide a surface for the plasterboard to fit to.

    I'll look into acoustic plasterboard, that might be cheaper considering the extra work building up the studs.

  5. Jimbo

    Jimbo Screwfix Select

    Yes. PIR needs an air tight seal to do anything to make sure it’s foamed and taped in before building out into the room. If you can accommodate 100mm rockwool that would be better with out the cladding basically to outside.
  6. new666uk

    new666uk New Member

    Thanks @Jimbo not quite following that last sentence.

    I've loads of aluminium tape to seal up the PIR so I'll have a seamless metal skin. Stealing a further 100mm off the inside dims will be too big a compromise really.
  7. Jimbo

    Jimbo Screwfix Select

    Fair enough. “With only cladding” (ie no brick) I had meant to write.

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