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General: Sheepswool vs Woodfibre for walls

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  1.  
    • CommentAuthorbobso
    • CommentTimeOct 1st 2024
     
    Hi all

    Trying to internally insulate our old coal shed. (now a study, which has been previously plastered (badly) and has various wires/ cables in the walls.

    Trying to do this in natural (read water permeable materials) to help control moisture/ warmth in the shed.

    Two options seem to be open to me:

    1) Sheep’s wool - So Bricks, Breather membrane, Wool, AVCL, Plasterboard (and held up by battens as thermal bridges) But does let us hang pictures/ shelves to the studs.

    2) Woodfibre - So Bricks, Lime coat, Woodfibre, Lime plaster (not too many thermal bridges, but hanging shelves etc difficult),

    Which is best from a breathability / insulation perspective? While the coal shed isn’t wet; but it is single skin brick... Likely can do 100mm of either insulation, so both work out at a U of approx. 0.3.

    If we go sheep’s wool, which seems easier to install / more like what our builder has experience with (And less lime plaster!), how much prep of the internal wall do we need to do? - i.e. does it have to be smooth etc for the membrane to go on? - Or would an old plaster and paint be ok?

    Thanks for any insights!
  2.  
    I have heard several horror stories with sheep's wool and moth infestations. If you don't have it very sealed in, then I think it can be tricky to prevent this. Even with the various borax type treatments.

    So personally wood fibre is the way to go. I've never physically installed it myself but have spoken to plenty of people who have, and it seems to be quite user-friendly to the novice. Essentially you lime plaster up the underlying wall substrate (which acts as an airtightness layer) and the soft woodfibre adapts to the wall surface. Then lime plaster over the top and use a breathable paint.

    When I specified this approach to an art gallery we were worried about hanging things, but you can get board-faced woodfibre boards specifically designed to give a flat inner surface and which can accept some fixings. We actually had the room to add a sacrificial timber stud & plasterboard lining which was free-standing about 25-50mm inside the IWI that acted as a services zone for wiring etc. too. Depending on your floor space, either of those approaches might work for you.

    Hopefully @sgt_woulds will be along shortly to give you more specific industry info.
    •  
      CommentAuthordjh
    • CommentTimeOct 2nd 2024 edited
     
    Hanging things off woodfibre shouldn't be a problem. We fastened things to lime-plastered straw bales! As already mentioned you can finish with plasterboard, see e.g. https://www.backtoearth.co.uk/guide/internal-wall-insulation-with-plasterboard-finish/ or you can get special wide screw-in plugs e.g. https://www.backtoearth.co.uk/product/spiral-fixings-insulation-systems/ or you can glue in a piece of solid wood and fasten into that. (copious epoxy fixes many things).

    Is the shed single skin brick? If so how do your designs prevent damp (rain) from penetrating through the brick and whatever is inside? i.e. where's the drainage plane?
  4.  
    Posted By: bobsoWhile the coal shed isn’t wet; but it is single skin brick

    And probably doesn't have a DPC (?)
    I would be concerned about any insulation that would degrade / rot if it got damp.

    If it were mine I would be thinking of EPS fixed with adhesive and moisture resistant plasterboard over that again fixed with adhesive. Lightweight things (pictures) fixed to the plasterboard and any shelves screwed through to the brickwork.

    For shelves I would use vertical shelf rails with the bottom of the rails sitting on the floor, they can look a bit utilitarian but they take the load off the wall.
    • CommentAuthorArtiglio
    • CommentTimeOct 2nd 2024
     
    I have ( by sounds of it) a very similar addition on side of my place, originally a coal store, had a toilet added at some point , then altered again to provide a bathroom. 4” brick wall. Pitched slate roof. When i got it, the walls were battened 50mm of fibreglass and plasterboard. When stripped out only water ingress in 40 years had been where lead flashing between main house and coalshed roof had split.
    It was built in 1935 so had a damp course in the walls but npthing in the solid floor. Floor came up for drainage and tovrun additional ventilation to the under floor void in mainhouse, so a dpm went in for good measure and 100mm celotex. Walls have little exposure to the weather , i bonded 40mm of steico to and baumit plasters over. Made sure the roof and gutters were good.
    3 years later no problems whatsoever. It serves as a boiler /utility room with a wc separate at one end. So always warm and has an extract for the mvhr . Certainly not a text book approach. As for fixing to walls, i use 60mm plastic wall plugs, drill to full depth of the woodfibre/plaster, glue the plug in with an foaming pu adhesive, trim off any excess plug, fine for light loads ( pictures, holding cabinets in place) i see it as being as good as a standard plasterboard fixing.
  6.  
    Posted By: ArtiglioIt was built in 1935 so had a damp course in the walls......... Floor came up for drainage............... so a dpm went in for good measure................ . Walls have little exposure to the weather...................It serves as a boiler /utility room with a wc separate at one end. So always warm and has an extract for the mvhr

    All important factors in governing the success of the project.

    If bobso's project is missing these features then account should be taken of the missing ones. IMO A DPC and weather exposure being the important ones.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 3rd 2024 edited
     
    Posted By: djhIs the shed single skin brick? If so how do your designs prevent damp (rain) from penetrating through the brick
    Posted By: bobsoWhile the coal shed isn’t wet; but it is single skin brick
    but does that mean 9" or 4.5"?
    • CommentAuthorbobso
    • CommentTimeOct 4th 2024
     
    Thanks for all the replies. :)

    To clarify it is double brick thickness (but no cavity). Mostly structure seems in good nick having taken the plaster off the walls last night. We also have a DPC.

    Project wise:

    Based on no positive sheeps wool votes - I'm planning to fill in any previous brick holes with a rough lime plaster, then mount wood fiber boards, followed by another lime plaster coat.

    Presume I don't need any breather membranes in this? - Are rigid boards (isolair), or softer (pavatex) type boards better?

    Which is better greenlime, steico or Pavatex itself? - Or are they all the "same"....?

    DPC wise - We've got one... So with the floor up, we're tanking in a DPM membrane to make it better and then going to take that up behind the insulation.

    Thanks everyone for their help, just building control people to please next!
  9.  
    Whoever you go to should provide you with a WUFI calculation that will determine moisture risk. In fact I'd go as far as to say that this should be the determining factor in whether you go Steico/Gutex or others.

    Maybe also have a read of this:

    https://woodfibreinsulation.co.uk/choosing-the-right-wood-fibre-insulation-manufacturer/


    For what it's worth I think the woodfibre does the equivalent of a breather membrane in its dense construction, so I don't think you need a separate one, but WUFI should tell you this.

    Clearly keeping moisture from getting through the brickwork behind it is the key thing to ensure.
  10.  
    Posted By: bobsorying to internally insulate our old coal shed. (now a study, which has been previously plastered (badly) and has various wires/ cables in the walls.

    Posted By: bobsojust building control people to please next!


    It sounds like it wasn't / isn't a coal shed and has already been used as something else - So do you need to get BC involved?
    •  
      CommentAuthordjh
    • CommentTimeOct 4th 2024 edited
     
    Posted By: Doubting_ThomasMaybe also have a read of this:

    https://woodfibreinsulation.co.uk/choosing-the-right-wood-fibre-insulation-manufacturer/
    Thanks. Excellent link.

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