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Home office / shed - insulation question

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  • 12-10-2020 4:10pm
    #1
    ZV Yoda
    Registered Users Posts: 1,447 ✭✭✭


    Looking for insulation advice.

    We have a 6m x 3m garden shed that was built around 16 years ago. Pretty solidly built, has electrics & water, but no heating other than 2 Dimplex oil filled heaters. It's cavity block construction, external wet render (I think that's what it's called).

    Internally, 12.5mm foil-backed plasterboard is fitted to battens. There's 25mm white polystyrene insulation between the battens. Walls are skimmed & painted. Hipped roof with attic space. uPVC door & 2 (smallish) double-glazed uPVC windows. The ceiling is also plastered, skimmed and insulated with 100mm glass wool between the joists. The attic is floored with chipboard. No roof insulation (i.e. cold roof).

    It's had occasional use as storage, and as a small music studio. It's going to get a lot more regular use now as a home office / music studio. So, I'm upgrading the interior.

    The ceiling is way too high (2.7m) so I'm in the process of lowering it because the room will be easier to heat, have better acoustics (for music) and I'll get more attic space. Any ideas on the best insulation approach for the new ceiling?

    Currently, I'm thinking of 50mm insulated boards on the ceiling, with 100mm Rockool between the ceiling joists, then re-flooring the attic. (I have a load of 100mm Rockwool, so would like to make use of it where possible).

    Is it worth the hassle of upgrading the walls insulation too? I spoke with Kingspan this am to see if I could fix 50mm insulated boards over the existing walls, but they said I'd need to strip off the existing boards first - something to do with moisture build-up due to the vapour membrane (i.e. foil backing on the existing plasterboard). That feels like a lot of hassle.

    I've been researching various options, but I'm more confused now that when I started!

    Bottom line, I need the space to function as a comfortable office / music studio, and would like to get the insulation right so it's a comfortable place to work and thermally efficient.

    Any suggestions / comment appreciated.


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    #2
    Lumen
    Registered Users Posts: 31,015 ✭✭✭✭Lumen


    Is the attic supposed to be warm or cold?

    Warm: insulate the roof, don't insulate the attic floor.
    Cold: insulate the attic floor, don't insulate the roof.

    I don't think you're going to be able to do very much for the cold walls without re-doing the interior or exterior finish. You've essentially just got a 25mm cavity and that's fully filled already.

    Sheds are relatively hard to heat because there's such a massive surface area to volume ratio, so to get near house-level performance you need in excess of house-level insulation.


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    #3
    ZV Yoda
    Registered Users Posts: 1,447 ✭✭✭ZV Yoda


    Lumen wrote: »
    Is the attic supposed to be warm or cold?

    Warm: insulate the roof, don't insulate the attic floor.
    Cold: insulate the attic floor, don't insulate the roof.

    I don't think you're going to be able to do very much for the cold walls without re-doing the interior or exterior finish. You've essentially just got a 25mm cavity and that's fully filled already.

    Sheds are relatively hard to heat because there's such a massive surface area to volume ratio, so to get near house-level performance you need in excess of house-level insulation.

    Thx... the attic is meant to be cold - which is why the existing ceiling was insulated - and so will the new one.

    Yes, I'm looing to get house-level insulation... so what should I be (ideally) putting on the ceiling / walls?


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    #4
    Lumen
    Registered Users Posts: 31,015 ✭✭✭✭Lumen


    Do the acoustics need improving?

    How much wall thickness can you afford to lose?


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    #5
    ZV Yoda
    Registered Users Posts: 1,447 ✭✭✭ZV Yoda


    Lumen wrote: »
    Do the acoustics need improving?

    How much wall thickness can you afford to lose?

    Yes, the acoustics need to be improved. Aside from lowering the ceiling , I will also be installing acoustic treatment (bass traps, diffusers etc) in the room. I'm already covered on the acoustic side of things.

    It's a decent sized room, so I could afford to lose maybe 60-70mm from each internal wall (e.g. I could replace the existing 12.5mm plasterboard with 50mm insulated plasterboard fixed to the existing battens, and that would lose 50mm per wall). More hassle than I'd like, but willing to do it if that's what's needed.


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    #6
    Lumen
    Registered Users Posts: 31,015 ✭✭✭✭Lumen


    ZV Yoda wrote: »
    Yes, the acoustics need to be improved. Aside from lowering the ceiling , I will also be installing acoustic treatment (bass traps, diffusers etc) in the room. I'm already covered on the acoustic side of things
    Ah right. I was just thinking that if you're re-doing the walls anyway you could make them non-parallel to reduce echos. But I'm not a sound engineer. :)


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    #7
    ZV Yoda
    Registered Users Posts: 1,447 ✭✭✭ZV Yoda


    Lumen wrote: »
    Ah right. I was just thinking that if you're re-doing the walls anyway you could make them non-parallel to reduce echos. But I'm not a sound engineer. :)

    I think the overall shape is fine for recording / mixing once I install diffusers and bass traps.

    So, in terms of insulation, should I bite the bullet and rip off the existing boards and replace them all with 50mm insulated boards?

    Or is there a better option?


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    #8
    ZV Yoda
    Registered Users Posts: 1,447 ✭✭✭ZV Yoda


    Spoke to Xtratherm this am and they gave the same advice as Kingspan - do not install insulated boards over existing foil-backed plasterboards.

    My current thinking is to remove all plasterboard, leaving the existing 25mm polystyrene between the battens. Then I'll install 62.5mm insulated boards (i.e. inc 50mm bonded insulation) over that. That would give me 75mm total insulation on the walls.

    I'll board the ceiling with the same 62.5mm insulated plasterboard, and for extra insulation, also put the 100mm Rockwool between the joists.

    How does all of that sound?


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    #9
    Lumen
    Registered Users Posts: 31,015 ✭✭✭✭Lumen


    I think you're proposing to have impermeable insulation flush against the inner face of an external cavity block wall. IMO that's a bad idea, to have no cavity, as there's a risk of moisture getting trapped.

    I don't use this kind of insulation myself, so I was hoping that others would jump in with specific suggestions, but since that hasn't happened yet, my suggestion is to remove the polystyrene and vent the new cavity (which will be formed between the battens) to the outside.

    And make sure your insulation is continuous and air tight on the warm side.


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    #10
    ZV Yoda
    Registered Users Posts: 1,447 ✭✭✭ZV Yoda


    Lumen wrote: »
    I think you're proposing to have impermeable insulation flush against the inner face of an external cavity block wall. IMO that's a bad idea, to have no cavity, as there's a risk of moisture getting trapped.

    I don't use this kind of insulation myself, so I was hoping that others would jump in with specific suggestions, but since that hasn't happened yet, my suggestion is to remove the polystyrene and vent the new cavity (which will be formed between the battens) to the outside.

    And make sure your insulation is continuous and air tight on the warm side.

    Isn’t that the situation as it currently stands though? The aeroboard is flush against the wall. Both Kingspan & Xtratherm agreed with this approach.


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    #11
    delly
    Moderators, Home & Garden Moderators, Recreation & Hobbies Moderators Posts: 7,653 Mod ✭✭✭✭delly


    Thread moved from DIY at OPs request.


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    #12
    Woodie.ie
    Registered Users Posts: 22 ✭Woodie.ie


    Have done this with a new stand alone extension, the spec for insulation was 50mm batten with 80mm polystyrene backed plasterboard. The cavity formed between and around the battens was a sealed warm air cavity where i used foam canisters to seal along where ceiling meets the block wall


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    #13
    Woodie.ie
    Registered Users Posts: 22 ✭Woodie.ie


    Have you considered doing external insulation.


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    #14
    ZV Yoda
    Registered Users Posts: 1,447 ✭✭✭ZV Yoda


    Woodie.ie wrote: »
    Have you considered doing external insulation.

    External wouldn’t have been practical. In the end, I removed all the existing plasterboard and re-slabbed the walls & ceilings with 72mm insulated boards onto the existing battens. I left the existing aero board in place. That was on the advice of 2 different plasterers and Xtratherm. There was no trace of damp behind any of the old boards.

    For added peace of mind, I laid 4” Rockwool between the ceiling joists above the 72mm ceiling plasterboards. The attic above that is floored with chipboard.

    I filled any wall / ceiling gaps with expanding foam before I got the plasterer in to skim the whole thing. There are 2 air vents in the walls for ventilation.

    I’ve laid a floating plywood base on top of the existing concrete floor. I’ll be laying laminate on top of that.

    Should be a pretty decent level of insulation by the time it’s finished. Delighted with how it turned out so far. Just needs to be painted & fitted out now.


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