Green Building Forum - Bathroom breathable insulation and tiling? What are our options? Tue, 19 Dec 2023 08:34:57 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300783#Comment_300783 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300783#Comment_300783 Fri, 17 Mar 2023 22:19:01 +0000 bgasparotto
As we progress throughout our rooms, we are now planning the bathroom of our Victorian/Edwardian house with solid brick walls.

After removing fittings, tiles and some paint, we uncovered what seems to be gypsum plaster and a bit of cement render, which is cracking and all patchy so we are planning to remove it and start again from the bare brick. This external wall (please see the picture) is where the insulation and bathtub + shower would be going and the window size reduced to half of what it is now.

We are aware that these types of houses need to breath so as we insulate the internal walls (EWI not an option), we will be using wood fibre boards throughout the rest of the house. But does that also apply for bathrooms (wet rooms)? If so, what would be an adequate tiling option on top of the insulation? We wonder if bathroom walls still need to be breath or whether we should make it water tight and rely on ventilation for the exchange of moisture.

We are quite new on retrofitting so we still don't understand whether we draw the line on breathability on kitchens/bathrooms or the same approach (IWI with wood-fibre + lime plaster) should be religiously applied on the entire house.

Any advices are welcome! We wish you all a lovely weekend :))]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300788#Comment_300788 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300788#Comment_300788 Sat, 18 Mar 2023 10:55:35 +0000 ChrisinYorkshire
We went for a hybrid option, the main external wall we did with wood fibreboard and lime plaster and painted, with no tiling other than a tiled skirting. Our bathroom is located on the ground floor and we chose to put a plinth later of XPS at the base of the wall, which sat directly on the concrete slab. This mitigated the otherwise risk of the wf boards sitting on a potentially damp concrete slab.

We had one partially external wall which would be regularly soaked in water from the shower and which the bath was set against. This was to be tiled, so here we used marmox XPS (siliconed all the joints) and covered them with their waterproofing tape. This is therefore a non-breathable wall.

As the floor is a concrete slab we put down marmox XPS on that and tiled over. I didn't like the idea of floating chipboard/OSB over PIR as used elsewhere in the house, in case of water damage. We have a freestanding acrylic bath that sits on the tiles and there's no issue with the weight. The XPS can take considerable loads where they are spread out.

We made sure that all external walls were pointed in lime mortar.
Made sure everything was airtight with appropriate pro-clima tapes.

Been in place for two years, the woodfibre wall gets the odd splash and it's been no problem at all..

We do get a slight issue with condensation gathering towards the lower part of a solid internal partition wall, which sits directly on the slab, so acts as a cold bridge.

Good mechanical ventilation is really important! We went for a single room mvhr with humidistat and automatic purge option. A decent extractor fan with built in humidistat would be fine.

Hope that helps, can post some photos when I get a minute

Good luck!

Chris]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300791#Comment_300791 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300791#Comment_300791 Sat, 18 Mar 2023 11:24:08 +0000 djh
All the internal walls are covered in XPS panels (Bushboard Nuance). No tiles, because SWMBO hates cleaning grout. And again as Chris says, ventilation is important. In our case each room has an MVHR terminal, of course.]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300814#Comment_300814 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300814#Comment_300814 Sun, 19 Mar 2023 18:21:22 +0000 bgasparotto
This external wall will get a fair amount of water as the bathtub and a shower will be right in front of it. So I am getting the idea that I should avoid getting the wall too wet?

Would tiling over the wood fibre and lime plaster be a reasonable option, so I sacrifice breathability but prevent the dampness?

Good tip about the marmox XPS and stormdry, the floor on this bathroom is concrete so it might create a cold bridge. We do plan to install underfloor heating though, so hopefully that will help?

I am all for breathability, but I feel a bit puzzled about bathrooms!]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300817#Comment_300817 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300817#Comment_300817 Sun, 19 Mar 2023 19:29:53 +0000 Nick Parsons
ChrisinYorkshire, is it really 2 years? My shoulders ache at the memory!]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300819#Comment_300819 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300819#Comment_300819 Sun, 19 Mar 2023 19:51:57 +0000 djh Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300822#Comment_300822 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300822#Comment_300822 Sun, 19 Mar 2023 23:38:14 +0000 bgasparotto
Is having some justifiable non-breathable walls expected with IWI or would I risk long term damage if I go this route?

If it helps, the ground level outside is quite low compared to the house so I don't see a risk of rising damp. Not sure whether this renders the breathability of this room less important or that is just the basics of a well maintained house.]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300824#Comment_300824 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300824#Comment_300824 Mon, 20 Mar 2023 07:51:58 +0000 Nick Parsons https://www.gov.uk/government/publications/retrofit-internal-wall-insulation-best-practice

If you read the BP guidance above (released, but apparently almost imperceptibly, by BEIS just around a year ago) you will see that they recommend that any non-breathable insulant should be used on IWI *only* where a fully ventilated air-space of at least 25mm can be 'engineered' between it and the wall. Anything else, I guess they would argue, is 'on your own head'. This is good advice, but it will complicate a lot of people's thought-processes. The example I used earlier did not have an air-gap, but it was done with an almost anal obsession with air-and vapour-tightness.]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300903#Comment_300903 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300903#Comment_300903 Wed, 22 Mar 2023 21:51:17 +0000 number_thirty_three
A breathable natural material for finishing wet areas such as a bathroom is Tadelakt. It's lime+ finished with an olive oil rub on the walls, so it's waterproof (ish - well, as I have understood it is similar to a tiled wall in that grout itself isn't waterproof either), and can also be used on the floor - if it's a wet shower room, for example. It's not a massively cost-effective option but if compared to a fully tiled bathroom i believe fairly similar. A lime plasterer should be good to apply it (or you can even have a go yourself if you fancy it because the finish is quite forgiving!)

If you have a google, you'll see some examples of it looking stunning and has become one of those finishes adopted to create a strikingly attractive bathroom, like Microcement, but has the benefit of being super sustainable. Perhaps worth considering for your circumstances.

We are planning on Marmoleum flooring for the bathrooms (this is basically Lino - but the original stuff - so 97% linseed oil based), which is also relatively good if you're planning on having UFH as it is only 2mm thick.

Agree with the earlier comments that if you're going to tile it then it's not going to be breathable - so keep an airgab behind. I would say that if you're keen (like we are) to use natural insulating materials, you could go for sheepswool (cheaper than wf), battened out to create the ventilated void behind - but depending on the depth you're going for this may not give you an amazing overall u value.

What do you plan to do with the pipes that run along that external wall? Will you be moving them inboard of the insulation or are they going somewhere else?

It's not clear from the pic if this is a ground floor or first floor?

Re woodfibre in bathrooms - friend of mine has wf on their exterior bathroom walls and it's fine to handle the moisture content - dries well if it gets wet but again as another poster has said, make sure you've got ventilation - my friend has a good mvhr system throughout. Bathroom shower curtain dries pretty swiftly after shower - useful indicator.

Re woodfibre in kitchens - absolutely no issue, again I know a couple of people with this. One has finished with just the lime - there really is no need for tiles (I mean from a technical perspective - they're largely aesthetic).

Remember though to use breathable paints on top (I mean, you probably know this but I feel like I need to point this bit out in case someone else reads this :bigsmile:!).

HTH]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300915#Comment_300915 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300915#Comment_300915 Thu, 23 Mar 2023 12:07:10 +0000 djh Posted By: number_thirty_threeI've done a lot of thinking and research on bathroom/kitchen finishes in the past, although we're still ages away from actually doing ours!It sounds like you've been through a lot of the same processes we did.

A breathable natural material for finishing wet areas such as a bathroom is Tadelakt. ... It's not a massively cost-effective option but if compared to a fully tiled bathroom i believe fairly similar. A lime plasterer should be good to apply it (or you can even have a go yourself if you fancy it because the finish is quite forgiving!)
We looked at tadelakt for our downstairs wetroom, for the outside wall I mentioned elsewhere. Our lime plasterer, Arthur Philip, was quite keen on it. It is very expensive though, because it's an enormous amount of hard work.

We are planning on Marmoleum flooring for the bathrooms
I would have liked to use marmoleum in various places but was put off by the limited choice of colours. In the wetroom we went for contract hospital vinyl installed by a local commercial firm, mainly to get the roughened anti-slip surface but also to guarantee a truly waterproof finish to form a shallow dish. It has done the job. Bamboo is an excellent flooring material; very stable and scratch resistant and stands up to water much better than a wood floor. Looks good too.]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300928#Comment_300928 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=300928#Comment_300928 Fri, 24 Mar 2023 10:55:19 +0000 Mike1 Posted By: number_thirty_threeA breathable natural material for finishing wet areas such as a bathroom is TadelaktIt's a good (and good looking) material but, due to its increased commercialisation, check the ingredients before buying to see what else may have been added (anti-crack fibres, acrylics, etc).

Also worth knowing that it does require simple but regular maintenance with olive oil soap to retain its water resistance, and it needs to be somewhere where it will dry out daily.]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301000#Comment_301000 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301000#Comment_301000 Wed, 29 Mar 2023 13:18:32 +0100 jwd I think it is worthwhile understanding what the purpose of breathable insulation is ... As far as I understand breathable insulation is for getting interstitial moisture out of walls not helping remove moisture from the air in a a bathroom. That is what ventilation is for.

There are obvious merits to insulating the walls as this will reduce/prevent condensation on the walls. I also think it important to consider wall coatings. Tiles are obviously a vapour barrier but so are almost all emulsion paints. interestingly while paints typically used in bathrooms in the UK often are very waterproof and contain ant fungicide, in Italy and other Mediterranean they use a chalky ,dusty paint to cope with condensation. I am talking here about ceiling and walls that wont be exposed to direct water rather than wall next to a bath or shower where a waterproof surface is essential.

The concept of moisture buffering surfaces is very useful here. This is the ability for some materials to absorb and hold moisture during times of peak humidity and release it slowly in drier periods - not unlike thermal mass in effect. I did an MSc at CAT a few years back and researched this very topic for my dissertation. I looked at bathrooms as they have intermittent but very high humidity levels -reaching 99% RH for short periods. Ventilation is needed to maintain healthy humidity levels but this results in heat loss and so needs to be balanced.

To test the effects of material choice I created an insulated, vapour tight chamber, with a humidity controlled ventilation fan. I measured the air movement, the humidity and temp of the outside air and the internal air. In one condition I lined the chamber with conventional foil backed plasterboard with gypsum skim and painted with standard emulsion paint. In the second condition I used conventional foil backed plasterboard coated in a lime/ hemp fibre plaster skim and a clay paint. The plaster I used was Adaptavate Breathaplasta. I also took a small sample of each and suspended it from a set of scales in the chamber so I could measure the changes in mass as the material absorbed and desorbed moisture. For each condition I humidified the chamber using a steam generator twice a day for 7 days. I found that the moisture buffering lime hemp plaster/ clay paint combination resulted in lower humidity levels in the air in the chamber and reduced the need for ventilation by about 30%. Within an hour of a steaming event the lime hemp plaster had fully dried out. I should caution that my setup was rather heath robinson and that wildly varying external temperatures and humidities ( the weather was very changeable at the time) could have confounded results so I cant be totally sure of my results but it does suggest that we can manage moisture levels very effectively by exploring moisture buffering wall coatings rather than the UK convention of super water tight surfaces.

Food for thought.

BTW the plaster skim was 4mm thick as the moisture doesnt penetrate far into the surface according to the research papers i read in preparation for my experiment. I should also add that the breathaplaster was really easy to use. I got a plasterer friend to prepare my samples and he commented that it was no more difficult to use than a gypsum skim. The surface was slightly rougher than gypsum but not noticeably so. The hemp fibres were so fine that you really couldnt tell they were there. According to my back ground research the hemp was the vital ingredient.
I hope this is of some interest

JwD]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301042#Comment_301042 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301042#Comment_301042 Thu, 30 Mar 2023 20:24:56 +0100 djh
As you say breathable insulation is about passing vapour through from one side to the other. Hygroscopic insulation also does buffering. These are mostly organic materials such as hemp, woodfibre, straw, wool, paper (warmcel) plus clay as the exception due to its microstructure.]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301079#Comment_301079 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301079#Comment_301079 Sat, 01 Apr 2023 13:31:38 +0100 bgasparotto
Posted By: Nick Parsonsthey recommend that any non-breathable insulant should be used on IWI *only* where a fully ventilated air-space of at least 25mm can be 'engineered' between it and the wall.

Posted By: number_thirty_threesheepswool (cheaper than wf), battened out to create the ventilated void behind - but depending on the depth you're going for this may not give you an amazing overall u value.

So in this case, it seems I can then install 25mm battens vertically then insulate + tile on top? Tadelakt seems really interesting though, but if we can make the tile route work that should be a winner for us.

When you say "ventilated" air-gap, does that mean I need to install some ventilated bricks to let air through the gap? I worry about infestations as this would be an unsupervised space once we are done with it.


Posted By: number_thirty_threeWhat do you plan to do with the pipes that run along that external wall? Will you be moving them inboard of the insulation or are they going somewhere else?

It's not clear from the pic if this is a ground floor or first floor?

This is a ground floor bathroom with screed floor (the only screed floor on the ground floor)
As for the water pipes I thought I would have them behind the insulation? I read on some WF manufactures installation guides that services should go behind the insulation (between the WF and the brick).
For the discharge pipes they will have to go through the wall to the outside, so I think it might create a small cold bridge?

Also Mike1, jwd and djh, thank you too for sharing all your wisdom! :)]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301082#Comment_301082 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301082#Comment_301082 Sun, 02 Apr 2023 12:25:50 +0100 Nick Parsons Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301084#Comment_301084 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301084#Comment_301084 Sun, 02 Apr 2023 16:02:01 +0100 djh Posted By: bgasparottoFor the discharge pipes they will have to go through the wall to the outside, so I think it might create a small cold bridge?Yes any pipe going through the external wall will create a cold bridge. Use plastic rather than copper to minimise conduction. Put a bend of some kind on the outside (e.g. turn a horizontal overflow downwards) to minimize airflow. Combine as many pipes as possible into one inside the building. All this assumes you can't go down through the floor of course, which is a better choice where possible.]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301088#Comment_301088 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301088#Comment_301088 Mon, 03 Apr 2023 08:29:09 +0100 GreenPaddy
you mentioned you are planning to screed the floor. Will there be insulation below that screed? My question relates to the pipes, which would be better run in that insulation, under the floor, rather than round the external wall(s), outboard of insulation, where there's a chance they could freeze (if the house were vacant for a period...winter holiday). Or can you run them under any built in cabinets or the bath?

Hard to tell from the photo, but have you removed a suspended floor, now exposing the solum, to be replaced with a solid floor? I think I can see a drain pipe running along the floor/solum??

Sort out the pipe routing first, then that clears the walls for insulation. I wouldn't worry at all about using non-breathable IWI for this room. It will be a small proportion of your house wall surface area. A large part of one of the ext walls is window anyway. Forget about the vented void, just adhere the IWI well to the wall behind (plus fixings), and try to ensure the VCL is as intact as you can make it.]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301096#Comment_301096 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301096#Comment_301096 Mon, 03 Apr 2023 23:31:29 +0100 bgasparotto Posted By: Nick ParsonsNot sure I would want (by which I mean I definitely would not want!) services behind the insulation (on the 'cold side'). Not least if you end up with a VCL (or at very least an air-tightness layer) you don't want to bu**er that up when you need to reach the pipes or cables.
Hmm that is an interesting point! I am planning to do as such because this is the recommendation I found from a few suppliers! Here is one (please see page 2: precautions): https://www.ecomerchant.co.uk/pub/media/productattachments/files/Ecomerchant_IWI_installation_guide.pdf

That said, we are getting the house rewired in a week, so I asked our electrician to install all wall cables inside of oval plastic conduits to help with maintenance if we need it in the future. If I top this up with installing the pipes in front of the insulation (but hidden under cupboards, etc), do you think it would make it better?

Posted By: djhYes any pipe going through the external wall will create a cold bridge. Use plastic rather than copper to minimise conduction. Put a bend of some kind on the outside (e.g. turn a horizontal overflow downwards) to minimize airflow. Combine as many pipes as possible into one inside the building. All this assumes you can't go down through the floor of course, which is a better choice where possible.

Not sure I can fit them under the floor, but I can definitely bend them horizontally on the outside. Thanks for the advice!]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301097#Comment_301097 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301097#Comment_301097 Mon, 03 Apr 2023 23:43:49 +0100 bgasparotto Posted By: GreenPaddyyou mentioned you are planning to screed the floor. Will there be insulation below that screed? My question relates to the pipes, which would be better run in that insulation, under the floor, rather than round the external wall(s), outboard of insulation, where there's a chance they could freeze (if the house were vacant for a period...winter holiday). Or can you run them under any built in cabinets or the bath?

Hard to tell from the photo, but have you removed a suspended floor, now exposing the solum, to be replaced with a solid floor? I think I can see a drain pipe running along the floor/solum??
Actually there is already screed in the floor! Sorry I can't take another picture at the moment as I am not home. To be honest I am still not sure what to do with this floor. I plan to install UFH on the rest of the house, but this bathroom has a solid screed floor that is preventing me from insulating it. I do consider removing the screed to insulate but I am unsure about how much work that will be and whether this could be too damaging to the building.

Posted By: GreenPaddySort out the pipe routing first, then that clears the walls for insulation. I wouldn't worry at all about using non-breathable IWI for this room. It will be a small proportion of your house wall surface area. A large part of one of the ext walls is window anyway. Forget about the vented void, just adhere the IWI well to the wall behind (plus fixings), and try to ensure the VCL is as intact as you can make it.

This bathroom is side by side with the kitchen which will also have tiles up to around ~140cm high from the internal floor. Would the combination of both alongside change the advice on this?]]> Bathroom breathable insulation and tiling? What are our options? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301102#Comment_301102 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17783&Focus=301102#Comment_301102 Tue, 04 Apr 2023 08:21:27 +0100 GreenPaddy
It would be such a shame to put UFH everywhere except the bathroom. You could then inset drains etc into the slab (eg. for shower tray) and not start off with compromises.

I think you said the floor level is quite a bit above the outside ground level, so ground based moisture/DPM's will be less of a risk factor.

Again, don't see an issue with parts of the bathroom and kitchen walls being non breathable, as so much of the house area will be breathable, and local extraction for peak vapour events (showering/cooking).]]>