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General: Best IWI for a bathroom

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    • CommentAuthordaveking66
    • CommentTimeDec 31st 2020
     
    I’d like to know what people think is the most appropriate IWI system for use in a bathroom.

    The bathroom In question has a bath, a shower and just one external facing wall measuring 2m x 2.8m high. I’ll be fitting a humidity activated extraction fan

    In general I’m leaning towards breathable systems as they seem to reduce the risks of interstitial condensation, but the Steico supplier (Ecomerchant) has advised that their boards should be covered with a layer of waterproof plasterboard if used in a bathroom - even though the wall will be dry (Ie with no adjacent shower)

    This makes me think I might as well just use PIR insulated plasterboard as it’s more efficient than Wood fibre.

    What are people’s thoughts?
    • CommentAuthortony
    • CommentTimeDec 31st 2020
     
    Good plan
    •  
      CommentAuthordjh
    • CommentTimeDec 31st 2020
     
    Make sure you don't use ordinary plasterboard. Use moisture resistant or one of the special water-resistant boards.

    How do you plan on finishing the surface? One option is to use XPS shower panels as both insulation and surface finish. The modern ones look good IMHO and are much better than products of yore.

    FWIW I have clay paint on lime plaster on straw bales in my showers. But I do have MVHR which reduces the humidity. I painted Stormdry on those bits of wall that I thought were most likely to get splashes and it seems to work.
    • CommentAuthorphiledge
    • CommentTimeDec 31st 2020
     
    Our bathroom has had standard plasterboard for the last 18 years with the only degredation being where a tile/shower tray joint had leaked. If you are reworking the whole bathroom, Id insulate all the internal walls to keep them warmer and help dry out quicker, particularly tiled areas.
    • CommentAuthordaveking66
    • CommentTimeDec 31st 2020 edited
     
    Posted By: tonyGood plan


    Which plan are you referring to?

    PIR insulated plasterboard? Or The Ecomerchant suggestion of Steico Wood fibre board Covered with a layer of waterproof plasterboard?
    • CommentAuthortony
    • CommentTimeDec 31st 2020
     
    PIR
    •  
      CommentAuthordjh
    • CommentTimeDec 31st 2020
     
    Posted By: philedgeOur bathroom has had standard plasterboard for the last 18 years

    Yes, our last bathroom had normal plasterboard without any problems. I still wouldn't recommend anybody to build that way! :bigsmile:
    • CommentAuthordaveking66
    • CommentTimeDec 31st 2020 edited
     
    Posted By: tonyPIR


    👍
    • CommentAuthorowlman
    • CommentTimeDec 31st 2020 edited
     
    <blockquote><cite>Posted By: djh</cite><blockquote><cite>Posted By: philedge</cite>Our bathroom has had standard plasterboard for the last 18 years</blockquote>

    "Yes, our last bathroom had normal plasterboard without any problems. I still wouldn't recommend anybody to build that way!"



    Especially if you're tiling
    • CommentAuthordaveking66
    • CommentTimeDec 31st 2020 edited
     
    Posted By: djhMake sure you don't use ordinary plasterboard. Use moisture resistant or one of the special water-resistant boards.

    How do you plan on finishing the surface? One option is to use XPS shower panels as both insulation and surface finish. The modern ones look good IMHO and are much better than products of yore.

    FWIW I have clay paint on lime plaster on straw bales in my showers. But I do have MVHR which reduces the humidity. I painted Stormdry on those bits of wall that I thought were most likely to get splashes and it seems to work.


    Am I right in saying that water proof plasterboard wouldn’t be necessary if I go down the PIR insulated plasterboard route?

    My understanding is that foil backed PIR board acts as a VCL

    The only place I was planning to use waterproof board Is in the shower (Hardibacker board)
    • CommentAuthordaveking66
    • CommentTimeDec 31st 2020 edited
     
    And I’m still unsure which IWI system is most suitable (if any) - let alone how it will be finished

    My issue with using PIR, particularly in the bathroom, is it’s reliance on the creation of an impervious seal around the periphery. Creating it successfully In the first place sounds difficult enough, expecting it to last as long as the building just seems too much to ask. So when it fails interstitial condensation seems inevitable.

    Is this an unfair assessment?
    • CommentAuthortony
    • CommentTimeDec 31st 2020
     
    Solution to interstitial condensation is EWI

    In my view it is better to stop moisture movement through or round insulation by using. A pour barriers on the warm side of the insulation, if the wall beyond the insulation is vapour open it will carry away moisture generally freeing the little there that remains safely away into the atmosphere and even when dew forms it will be on the very outside of the outer layer
  13.  
    Happy new year!

    Can anyone tell me if my quotes (of the other posts) are displaying ok? Thanks
    • CommentAuthorEd Davies
    • CommentTimeJan 1st 2021 edited
     
    Happy New Year.

    No, your quotes aren't displaying OK. You need to select “Format comments as” ”Html” below the “Enter your comments” box for <blockquote> and other such tags to work.

    An unfortunate quirk of this forum software is that if you do select Html then URLs don't get linkified. For those you have to select “Text”. You can have either formatting or clickable links, not both.

    You can fix your own old posts to make the formatting work. Click on the “edit” in the top right of your post, change the format selection then click “Save Changes”. Obviously there isn't an edit link on other people's posts.

    A couple of additional points about quoting in this forum's software:

    1) You can quote just a small part of the original post by selecting the text you want to quote before pressing the “quote” link but

    2) be very careful that you press the quote link of the right post. When selecting something from the end of a long post it's very tempting to actually click the quote link of the following post. This will quote the selected text but attribute it to the author of the post on which the quote link was pressed.
    •  
      CommentAuthordjh
    • CommentTimeJan 1st 2021
     
    Posted By: daveking66Am I right in saying that water proof plasterboard wouldn’t be necessary if I go down the PIR insulated plasterboard route?

    No, the point of moisture resistant plasterboard is that ordinary plasterboard can be ruined if it is exposed to a lot of moisture such as can be found in bathrooms. Waterproof boards such as Hardiebacker or Aquapanel are something else again - they are cement rather than plaster-based and are stronger. And then there are XPS insulated boards.
    • CommentAuthorbxman
    • CommentTimeJan 1st 2021
     
    Hi Dave

    I am puzzled

    My understanding is that the house is a straw bale construction as such it should be very well insulated .

    So what is the need for IWI ?

    You say the bathroom has only one external wall .

    Is there a cold bridge in that particular wall ?
  17.  
    Posted By: djh
    Posted By: daveking66Am I right in saying that water proof plasterboard wouldn’t be necessary if I go down the PIR insulated plasterboard route?

    No, the point of moisture resistant plasterboard is that ordinary plasterboard can be ruined if it is exposed to a lot of moisture such as can be found in bathrooms. Waterproof boards such as Hardiebacker or Aquapanel are something else again - they are cement rather than plaster-based and are stronger. And then there are XPS insulated boards.


    Ah ok I see. I was looking at water resistant plasterboard purely from the perspective of providing a barrier to prevent overloading the wood fibre insulation boards with moisture
  18.  
    Posted By: tonySolution to interstitial condensation is EWI

    In my view it is better to stop moisture movement through or round insulation by using. A pour barriers on the warm side of the insulation, if the wall beyond the insulation is vapour open it will carry away moisture generally freeing the little there that remains safely away into the atmosphere and even when dew forms it will be on the very outside of the outer layer


    Hmmm. So is the consensus that (Damaging amounts of) interstitial Condensation is inevitable with IWI?
  19.  
    Posted By: Ed DaviesHappy New Year.

    No, your quotes aren't displaying OK. You need to select “Format comments as” ”Html” below the “Enter your comments” box for
    and other such tags to work.


    Sorted! Thanks Ed 👍
    • CommentAuthordaveking66
    • CommentTimeJan 1st 2021 edited
     
    Posted By: bxmanHi Dave

    I am puzzled

    My understanding is that the house is a straw bale construction as such it should be very well insulated .


    Wrong bathroom I’m afraid!

    DJH has the enviably well insulated straw bale construction. Mine is a frigid solid brick job
    • CommentAuthorJeff B
    • CommentTimeJan 1st 2021
     
    I would use PIR. Then Aquapanel in the critical areas around the bath and shower and moisture resistant plasterboard elsewhere (it's much cheaper than Aquapanel!).

    I have used Hardibacker board but it is a beast to cut and I am wary of the dust generated in the process, even when using their special cutting tool. It is also quite heavy to handle. A positive is that they seem pretty indestructible!

    I wish I had discovered Aquapanel earlier as they are much lighter panels. Please note: I have no connection with the company and I haven't actually used these panels but having seen them and examined them at our local Wickes's store I would give them a try next time. Maybe another forum user could confirm if they are any good?
    • CommentAuthorbxman
    • CommentTimeJan 1st 2021
     
    sorry for confusion

    I used Multipanel 2400x1200mm unlipp grey marbl Multipanel 3 off for £267 from Plumbase back in 2011.

    it had both H & L chanel Ali joining strips

    absolutely no regrets it has worked well and looks as good as new.

    No idea if it is still available or present day price if it is.
    • CommentAuthorkristeva
    • CommentTimeJan 1st 2021
     
    Posted By: daveking66

    In general I’m leaning towards breathable systems as they seem to reduce the risks of interstitial condensation, but the Steico supplier (Ecomerchant) has advised that their boards should be covered with a layer of waterproof plasterboard if used in a bathroom - even though the wall will be dry (Ie with no adjacent shower)



    I guess they must be worried the wood fibre will become saturated with moisture in a breathable system, So I guess that must mean my bathroom walls of 200 year old brick and lime plaster must be saturated too.
  24.  
    Hi Dave, I'm in the middle of doing mine right now with a breathable/non-breathable hybrid, as follows:

    - woodfibre board with baumit plasters internally on one of the external walls. Externally the wall suffers from freeze/thaw action. (Thick solid walls of sandstone of varying density/porosity). I've also repointed in NHL 3.5. Internally this wall won't generally get splashed, but I'm looking at a clay glaze paint or silica/mineral paints for potentially vulnerable areas.

    We have another external wall in the bathroom, but it backs onto a passageway and is protected from the rain. This wall will have the bath and shower against it. I've gone for Marmox multiboard at 50mm for this wall (and the floor which is concrete slab). All board edges have had a bead of sealant. Any gaps at edges have been filled with sealant. I'm putting their fleecy buty(?) waterproof tape over the top of joints. All Marmox boards will then be tiled.
    •  
      CommentAuthordjh
    • CommentTimeJan 1st 2021
     
    Posted By: ChrisinYorkshireAll Marmox boards will then be tiled.

    We have Bushboard Nuance boards inside our showers - they're like the Marmox (XPS core) but have various decorative finishes so there's no tiling needed. In my case SWMBO hates tiles and especially grout lines. :bigsmile:
    • CommentAuthordaveking66
    • CommentTimeJan 1st 2021 edited
     
    I’ve used Marmox boards when insulating a floor before fitting underfloor heating. Agree it’s good stuff. V easy to cut and work with.

    Regarding the external wall to be insulated, (Which is away from the shower)
    I feel pretty sure I’m going to go for an ‘open moisture’ system though, ie wood fibre or similar after reading the following 90 page report, which is the most authoritative sounding and apparently well researched document on Solid Wall Insulation I have so far found:
    https://issuu.com/bristolcitycouncil/docs/a_bristolian_s_guide_to_solid_wall_?ff

    With PIR systems there just seems to be too much reliance on creating a VCL. I don’t have the time to do the work myself unfortunately and I’d feel nervous about relying on a contractor to be meticulous in its application.
    • CommentAuthordaveking66
    • CommentTimeJan 1st 2021 edited
     
    Posted By: daveking66
    In general I’m leaning towards breathable systems as they seem to reduce the risks of interstitial condensation, but the Steico supplier (Ecomerchant) has advised that their boards should be covered with a layer of waterproof plasterboard if used in a bathroom - even though the wall will be dry (Ie with no adjacent shower)


    Thinking about this further, covering the wood fibre boards with a water resistant plasterboard would appear to remove the main purpose of the breathable wood fibre system (unless water resistant plasterboard is breathable). The whole purpose of an open moisture system, as far as I understand, is to allow the external brick wall to evaporate any trapped moisture to the inside (as well as the outside). Applying a water resistant plasterboard seems likely to Inhibit the desired breathability.

    Have I got this right?
    What do people think?
  28.  
    ''Hmmm. So is the consensus that (Damaging amounts of) interstitial Condensation is inevitable with IWI?''
    No, but the thickness will be limited. 80-100mm wood-fibre, probably, subject to dynamic cond'n risk analysis.
    •  
      CommentAuthordjh
    • CommentTimeJan 3rd 2021 edited
     
    daveking66 said: "I feel pretty sure I’m going to go for an ‘open moisture’ system though, ie wood fibre or similar after reading the following 90 page report, which is the most authoritative sounding and apparently well researched document on Solid Wall Insulation I have so far found"

    FWIW, there's PDF version for those who prefer it at:
    https://sdfoundation.org.uk/wp-content/uploads/2018/01/2015_bristolsolidwallinsulationguidance.pdf
  30.  
    The 'Bristolian's guide...' is good, but IIRC the author is fairly dogmatic that 60mm WF should not be exceeded. Other opinions exist. I usually used 100mm Pavadentro (with its 'mineral functional layer') when it was available, but do your homework. 60mm would be 'safe', I think, in most situations (on the right sort of substrates, of course), but be prepared to stand your ground when BCO is looking for 0.3W/m2K. (The 'get-outs' are in AD L1B)

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