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Wall insulation for external bathroom

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  1. #1
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    Default Wall insulation for external bathroom

    Hi everyone,


    We're renovating the storage & bathroom/laundry which are outside of the main house in Sydney. So all the walls will be external and there is only 1 internal wall that separate the storage from the combined bathroom/laundry. The cladding will be blueboard with one layer of sarking between blueboard and studs (I don't know whether the sarking is permeable or non-permeable yet).


    We will put wall insulation for the storage (at least the 3 external walls). However, the builder advise against putting insulation for the bathroom as it will create mould due to high moisture from the combined bathroom/laundry.


    I tried to to search around but most of the information online is more US oriented where they have quite different climate to Sydney. Even within the US, there are different guideline on how to insulate the bathroom depending on the climate zone of the location.


    My questions are?
    1) Is it worth it to insulate the external bathroom in Sydney's climate?
    2) If yes, is there any guideline to prevent mould from happening?


    Thanks,
    MM

  2. #2
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    Ventilate it well and it should stay dry. I don't know about Sydney but here in Geelong we insulated as much as we could, all walls and ceiling, wet area plasterboard/tiles and a fan in the outer wall. Underfloor heating in winter
    "A big boy did it and ran away"

    Legal disclaimer denying responsibility to be inserted here.

  3. #3
    3K Club Member johnc's Avatar
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    You shouldn't have any issue insulating the bathroom, as long as the waterproofing is done correctly and there are no leaks you should be fine. Properly lined you shouldn't get moisture in the walls. You need a breathable fabric for your walls.

  4. #4
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    Quote Originally Posted by johnc View Post
    You shouldn't have any issue insulating the bathroom, as long as the waterproofing is done correctly and there are no leaks you should be fine. Properly lined you shouldn't get moisture in the walls. You need a breathable fabric for your walls.
    Thanks Moondog and Johnc for your reply!


    In terms of technical details, should I have the following in order from outside to inside:
    1) Blueboard outside
    2) then permeable sarking that dry to the exterieur
    3) Studs & Insulation (fiberglass or earthwool)
    4) Vapour barrier (non-permeable)
    5) Drywall
    6) Waterproof membrane
    7) Wall tiles


    Do you think (2) and (4) will create a vapour barrier sandwich and make it worse?


    I'm not sure if I should use:
    (a) Permeable or non-permeable for (2) and (4)
    (b) If permeable, which direction.


    Any advice is much appreciated. My builder doesn't seem to know about this so I might have to be very specific with him.


    Thanks,
    MM

  5. #5
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    Quote Originally Posted by MettaMaitri View Post
    Thanks Moondog and Johnc for your reply!


    In terms of technical details, should I have the following in order from outside to inside:
    1) Blueboard outside
    2) then permeable sarking that dry to the exterieur
    3) Studs & Insulation (fiberglass or earthwool)
    4) Vapour barrier (non-permeable)
    5) Drywall
    6) Waterproof membrane
    7) Wall tiles


    Do you think (2) and (4) will create a vapour barrier sandwich and make it worse?

    MM
    Do you think (2) and (4) will create a vapour barrier sandwich and make it worse? - short answer is no.
    Modern houses in Australia have all that you describe as standard layers (1. being the outside cladding of your choice) other than No:4. Generally USA have No4, not sure of other countries such as UK/Europe and cant be all that bad.

    No:5, Id be using cement sheeting (Villa board, or other generic standard description for the same product) for the shower/bath wall area. Yes you can use Aqua Check, the dry wall alternative but personally out of the 2 choices, nothing compares with cement sheeting as the backing board for your shower/bath tiles.

    The most important part is the waterproofing for your wet areas needs to be done correctly including all the "bones" built before the waterproofing is applied.
    If this fails, then all the rest is for nothing.

    With 2 bathrooms that have failed at the 5 year old mark, and with me demo'ing the bathrooms to see where and why they failed (they didn't come close to meeting the AusStandards) along with having some great experienced trades in the local area to chat to, its a lot more common than one might think. In most cases its poor workmanship including not applying the waterproofing product as per manufacture standards AND not as per the AS3740 Waterproofing of domestic wet areas standards which is a bare minimum requirement.

    Some of the learnings I'd taken away from the experience/project are:
    1. AS3740 Australian Standards on Waterproofing Domestic Areas - Get a copy to have a good understanding of the minimum requirements so you know if/when your being BS to. Remember this standard is the minimum requirements
    2. Liquid Membrane - Know what product your builder will use and the manufactures recommended application as they can vary including application times, thicknesses for each layer and the type of gap filler that the liquid membrane can be applied to. Using the incorrect gap filler can/will result in waterproofing failure at some future point. Ensure wait times are adhered to with when the liquid membrane can be applied over the screed. Make sure they use reinforcing bandage on all 90 degree joins and around the tap/shower rose exit points...very small cost for a longer lasting result (see the Gripset videos for further explanations) and strongly consider double waterproofing under and over the screed with correct drying times. Have a look at the Gripset Utube videos as they provide some good info regardless of what liquid membrane product you end up using...they are also an Aussie product that's been in the market for 15+ years.
    3. Epoxy Grout - think about applying epoxy grout to at least the shower base. Its is a bit harder to apply as its essentially a glue, and about an extra 1 hour worth or work for the tiler on a standard shower but it does add another layer of waterproofing and doesn't stain/mold up like standard grout. Not all epoxy grouts are the same (in terms of how easy they are to apply). I used Ardex based partly on someone here on the forum that been using it for a few years. Feedback from the tiler is it was good to work with
    4. Shower Screed - The company laying my semi dried concrete screed also adds a water proofing component to the screed but I don't believe this is a common practice....just an added bonus to the entire waterproofing protection
    5. Concrete Slab Shower inlay- make sure the shower inlay/recess is sloped to the drain point. Can be easily ground down with a concrete grinder prior to the walls going up o minimise dust inside. Feedback from other professional trades is this can be a point of failure as the water pools and never full drains within the screed.
    6. Large Format Tiles - If your using tiles on the shower walls and not going to apply epoxy grout to the walls, consider options such as large format tiles to both minimise grout in the shower (standard cement grout isn't waterproof) and the forever ongoing maintenance/cleaning. I'd ended up using 1200 x 600 cut to suit resulting in only 3 horizontal grout lines and the floor (4 wedges)
    7. Polymarble Base - If you use a pre-molded base, make sure its layed on a mortar base with no air pockets as this is a common point of failure due to the flexing of the base
    8. Wall Noggins - a nice to have is noggins in the wall between the studs to screw your shower shelf to and the bottom attachment of the shower rose if you end up having one of those rain heads/hand hose setup attached to the wall.
    9. Insulation Batts - We dont build to fail BUT in case it does, have your wall insulation behind the shower walls and 600 each side finish 100mm short of the base plate. Reasoning is in my case, the water coming through the failed membrane at the base 90 degree joins ended up soaking up into the wall batts and would have never dried out, compounding issues making the rebuild more costly through more damage if the failure wasn't identified until much later


    Also given you are a new build, have either a couple of 90x45 or 150x45 noggins in the wall for the towel rail/s to screw to.
    And the fan over the shower to extract out the steam which is a big difference over our previous place with the fan/heat lamp in the middle of the room

  6. #6
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    Quote Originally Posted by Bart1080 View Post
    Do you think (2) and (4) will create a vapour barrier sandwich and make it worse? - short answer is no.
    Modern houses in Australia have all that you describe as standard layers (1. being the outside cladding of your choice) other than No:4. Generally USA have No4, not sure of other countries such as UK/Europe and cant be all that bad.

    No:5, Id be using cement sheeting (Villa board, or other generic standard description for the same product) for the shower/bath wall area. Yes you can use Aqua Check, the dry wall alternative but personally out of the 2 choices, nothing compares with cement sheeting as the backing board for your shower/bath tiles.

    The most important part is the waterproofing for your wet areas needs to be done correctly including all the "bones" built before the waterproofing is applied.
    If this fails, then all the rest is for nothing.

    With 2 bathrooms that have failed at the 5 year old mark, and with me demo'ing the bathrooms to see where and why they failed (they didn't come close to meeting the AusStandards) along with having some great experienced trades in the local area to chat to, its a lot more common than one might think. In most cases its poor workmanship including not applying the waterproofing product as per manufacture standards AND not as per the AS3740 Waterproofing of domestic wet areas standards which is a bare minimum requirement.

    Some of the learnings I'd taken away from the experience/project are:
    1. AS3740 Australian Standards on Waterproofing Domestic Areas - Get a copy to have a good understanding of the minimum requirements so you know if/when your being BS to. Remember this standard is the minimum requirements
    2. Liquid Membrane - Know what product your builder will use and the manufactures recommended application as they can vary including application times, thicknesses for each layer and the type of gap filler that the liquid membrane can be applied to. Using the incorrect gap filler can/will result in waterproofing failure at some future point. Ensure wait times are adhered to with when the liquid membrane can be applied over the screed. Make sure they use reinforcing bandage on all 90 degree joins and around the tap/shower rose exit points...very small cost for a longer lasting result (see the Gripset videos for further explanations) and strongly consider double waterproofing under and over the screed with correct drying times. Have a look at the Gripset Utube videos as they provide some good info regardless of what liquid membrane product you end up using...they are also an Aussie product that's been in the market for 15+ years.
    3. Epoxy Grout - think about applying epoxy grout to at least the shower base. Its is a bit harder to apply as its essentially a glue, and about an extra 1 hour worth or work for the tiler on a standard shower but it does add another layer of waterproofing and doesn't stain/mold up like standard grout. Not all epoxy grouts are the same (in terms of how easy they are to apply). I used Ardex based partly on someone here on the forum that been using it for a few years. Feedback from the tiler is it was good to work with
    4. Shower Screed - The company laying my semi dried concrete screed also adds a water proofing component to the screed but I don't believe this is a common practice....just an added bonus to the entire waterproofing protection
    5. Concrete Slab Shower inlay- make sure the shower inlay/recess is sloped to the drain point. Can be easily ground down with a concrete grinder prior to the walls going up o minimise dust inside. Feedback from other professional trades is this can be a point of failure as the water pools and never full drains within the screed.
    6. Large Format Tiles - If your using tiles on the shower walls and not going to apply epoxy grout to the walls, consider options such as large format tiles to both minimise grout in the shower (standard cement grout isn't waterproof) and the forever ongoing maintenance/cleaning. I'd ended up using 1200 x 600 cut to suit resulting in only 3 horizontal grout lines and the floor (4 wedges)
    7. Polymarble Base - If you use a pre-molded base, make sure its layed on a mortar base with no air pockets as this is a common point of failure due to the flexing of the base
    8. Wall Noggins - a nice to have is noggins in the wall between the studs to screw your shower shelf to and the bottom attachment of the shower rose if you end up having one of those rain heads/hand hose setup attached to the wall.
    9. Insulation Batts - We dont build to fail BUT in case it does, have your wall insulation behind the shower walls and 600 each side finish 100mm short of the base plate. Reasoning is in my case, the water coming through the failed membrane at the base 90 degree joins ended up soaking up into the wall batts and would have never dried out, compounding issues making the rebuild more costly through more damage if the failure wasn't identified until much later


    Also given you are a new build, have either a couple of 90x45 or 150x45 noggins in the wall for the towel rail/s to screw to.
    And the fan over the shower to extract out the steam which is a big difference over our previous place with the fan/heat lamp in the middle of the room
    Thank you so much Bart1080! Really appreciate your detailed feedback. The builder will start tomorrow and I will tell him on those recommendation.

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