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Housing - Renovation: Insulating plaster - what about the internal walls?

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  1.  
    Keen to use a breathable insulating plaster on the inside of my external solid brick walls to reduce risk of condensation etc. But I am wondering what to put on the other internal walls? Normal plaster? I was looking at options such as Bauwer light but seems like it would be very costly to do every wall in the house in this stuff.
    • CommentAuthorjfb
    • CommentTimeSep 20th 2019
     
    I did all my internal walls with sand/hydraulic lime. I guess you could use a cement render but wouldn't be my choice. Or even dot and dab plasterboard then skim.
    I compared the cost of insulating plasters against woodfibre board/ lime render and for me it was much cheaper to use woodfibre board. But that is doing the work myself - if you are getting trades in it may not be the same. It also depends on the walls themselves. If they are pretty flat then it is much easier to apply the initial layer of render that the woodfibre boards go against. If it is a really wobbly wall then the insulating plaster option has some benefits.
    Some of the insulating plasters that have a better u value are really expensive. Consideration of how thick you can afford to go with the insulation is relevant as some of the basic insulating plasters need quite a thickness to achieve the same u value as woodfibre board.
  3.  
    They do look expensive yes. Even to my untrained eye. The house is not huge so I don't want to lose too much wall so I would go about 50mm thick maximum. The Bauwer light stuff says it dries for re-coating in a day whereas I think lime would time much longer? I suppose I could use a combination of lime plaster and insulating plaster but I might have to wait a long time for the lime to dry? What was your experience?
    • CommentAuthorjfb
    • CommentTimeSep 20th 2019
     
    Yes lime render can take a few days (or longer if cold and damp) to be ready for another coat. I haven't used the bauwer renders so can't speak for them. I know others have used bagged renders with success and have said they can be lighter to use than normal sand/lime renders.
    An initial flattening layer of lime/sand might be a good way to go to do a lot of the filling in of the stone work. It would certainly be a bit cheaper.
    I guess it depends how the work is being done. If you are doing multiple rooms at a time then it is less of an issue to use lime since you can carry on with another room while one is drying.
    Remember to make sure you damp down the walls first especially in dry weather it can take a good hosing. And afterwards it is good to damp it down a bit. Not sure about the bauwer stuff.
    • CommentAuthortony
    • CommentTimeSep 20th 2019
     
    Insulating plaster would need to be considerably thick, 0.5 to 1m to be of any use, even to comply with building regulations too thick to be sensible internally
    • CommentAuthorJeff B
    • CommentTimeSep 21st 2019
     
    <blockquote><cite>Posted By: tony</cite>Insulating plaster would need to be considerably thick, 0.5 to 1m to be of any use, even to comply with building regulations too thick to be sensible internally</blockquote>

    0.5 to 1.0m thick!! That can't be right can it Tony?
    • CommentAuthortony
    • CommentTimeSep 21st 2019
     
    What U-value do you want to achieve?
  8.  
    '' The house is not huge so I don't want to lose too much wall so I would go about 50mm thick maximum.''

    Have you spoken to Building Control yet? When you add or replace a layer to a thermal element such as an external wall (whether that layer is internal or external) you 'kick in' Part L1B of the Building Regs, which for a solid-walled house requires a U value of 0.3W/m2K. 50mm of Bauwer light will not reach that. There are some 'get-out clauses' for old houses built (as yours will have been) of water-vapour-permeable materials, but you have to apply for a Building Notice anyway, and argue for a waiver/'dilution' if applicable.

    If I remember rightly Bauwer Light has a lambda value (thermal conductivity) of 0.068W/mK. If your house is approx. 225mm solid brick it will be deemed to have a base-case U value of 1.7W/m2K. That equates to and R value of 1/1.7, or 0.588. Calculate the R value of the Bauwer Light by dividing the thickness (0.05m) by the lambda value (0.068) and you get 0.735m2K/W. Add the 2 and you get 1.323. 1/1.323 = 0.755 = the U value, so less than half as good as the Building Regs would normally require. The only thing that would get you near 0.3 (and not quite there anyway) would be phenolic foam, unless you have very deep pockets and go with Aerogel (Spacetherm).
    • CommentAuthorKenny_M
    • CommentTimeSep 23rd 2019
     
    There have been a few threads on insulated render/plaster etc. I was considering it previously, and in the below thread I did a cost comparison of Bauwer, Diathonite and Wood fibre. Wood fibre was considerably cheaper, but I was only considering materials, not Labour. My house is 200 years old. The only wall I have done internally I did with EPS and plasterboard, but this was in a bathroom, so I was thinking more about keeping moisture our of the walls rather than letting it breathe.

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14292&page=5
  10.  
    I previously read through the thread on Bauwer Insulated plaster/render and actually it was this that persuaded me that it could be suitable for my project. I have to admit to not being familiar with Building Regs and when they would kick in. Also have to admit to being a bit surprised that I would need to achieve a U value of 0.3W/m2K. It seems like a tall order for a solid wall and surely something is better than nothing?! But the rules are the rules I guess.

    I have been reading about Spacetherm. I will have a look at phenolic foam also.
    • CommentAuthorjfb
    • CommentTimeSep 25th 2019
     
    The rules are the rules but they are not designed while considering problems of interstital condensation in old solid wall buildings. That is why there is some leeway for historic buildings.
    • CommentAuthorKenny_M
    • CommentTimeSep 25th 2019
     
    I've been a bit confused too about the circumstances under which the regs kick in, because as you say, surely its better than someone adds insulation, than does nothing because they can't meet the regs.

    Someone posted something the other day that suggested that you don't need a building warrant when 'adding' insulation, and its also been said that if you can demonstrate that it would take more than 15 years for ROI, then that's another get out clause. Not suggesting that we should be looking for loopholes, but its going to be practically impossible to meet the regs on most very old houses, and I would rather do something than nothing.
  13.  
    The regs kick in as soon as you 'renovate' (add or replace a layer to) more than 50% of a thermal element (and if it's internal ins that's 50% of the external wall *in the room you are in*. You may be allowed leeway, and as I stated in my post above the regs allow for that, but you still have to (pay the money and) apply for a Bldg Notice.

    Look on Planningportal.gov.uk for Approved Doc L1B. Cannot remember the section no's but headings are fairly clear and it's all there.

    @modernvictorian, ''I have been reading about Spacetherm. I will have a look at phenolic foam also. ''

    Spacetherm very pricey but sometimes, for small areas with v little depth to play with, the only way to get a halfway-decent result. Need to use it in a loft conversion with a steel ridge and v restricted height below. Phenolic foam isn't 'breathable', and your house is.
    • CommentAuthorKenny_M
    • CommentTimeSep 25th 2019
     
    Correction to above, checked and what Will quoted the other day from the Scottish regs was that you didn't need to apply for a building warrant for improvements to internal insulation, 'providing' that it meets the standard anyway. So you do need to meet the regs, but you don't need to apply for a warrant (in Scotland). Incidentally, this is the same for stoves in Scotland, below a certain kW.

    Still, from a householder point of view this all seems quite bizarre. Does this mean that technically, Joe Bloggs who slaps on some of that insulated wallpaper stuff over the whole of an external wall, needs to apply for a building warrant? Or, it would be legal for him to leave his loft uninsulated, but illegal to add 200mm of loft roll? :)
    •  
      CommentAuthordjh
    • CommentTimeSep 26th 2019
     
    We shouldn't really have to be arguing about the desirability of EXCEEDING building regs on the green building forum, let alone be discussing ways to avoid even complying with the poor standards the regs require, IMHO.
    • CommentAuthorGreenPaddy
    • CommentTimeSep 26th 2019
     
    Life would be so much easier without building control, but we'd have even worse buildings than the rubbish that's been built in the past, and all too often still today. Agree with djh that we should be looking beyond BRegs, on this forum.

    I still get picked up on oversights on my drawings by building control (building standards officer), which have to be fully checked and comply before starting any work in Scotland, despite the fact that I generally design well above building regs set values. So they perform a really valuable (really annoying) role. The fact of having a second pair of eyes over viewing in itself is a good thing...we all have blind spots, especially in the attempt to achieve great insulation values, the structural, condensation, or fire safety conditions can be worsened. Insulation in the wrong hands can do a lot of damage.

    There is a valid point, in just understanding when you need to formally apply for the building warrant/notice, as you do need to read the fine print carefully, and then try to interpret. It can be a bit of a circular search, as one reg seems to be clear, but then the next may contradict, for a very specific job you happen to be doing, but it has to be a high level catch-all document.

    If you consider it as paying a relatively small fee (relative to many arch's fees), to have assistance that is in the best interest of building at least a minimum quality, it's worth just doing it if in doubt. If the job is such a rush that you can't afford to wait for it to be checked, then maybe the job is in "too much of a rush".

    If your "Joe Bloggs" fires in a load of insulation in his loft, with an old style felt under his slates, and blocks all the eaves ventilation, he may come back in a few years to find a load of rotting roof timbers...and that's about the simplest of possible home improvements.
    • CommentAuthorKenny_M
    • CommentTimeSep 26th 2019
     
    I don't think that's what the argument is djh. If I was doing a new build I would be looking to exceed the regulations, but in a retrofit of a very old house its often not possible, or at least not reasonably practical.

    What I am saying is that if the choice is between doing nothing, or improving insulation to less than the building regulations, then I think it is better to improve.
  18.  
    There's no question of avoiding compliance with building regs/Stds.

    AD L1B is quite clear what the required standard is for renovations in England:
    "5.9 .. the element should be upgraded to the best standard that is technically and functionally feasible and which can be achieved within a simple payback of no
    greater than 15 years. "

    If Jo/Joe Bloggs adds 200mm of loft insulation where there was none, because that's how much is feasible or economic in their situation, then s/he has completely complied with regulations. If they use 250mm, they have exceeded regulations.

    Jo will have reduced the U value by about 3.0W/m2K. If we compare this with Fred who took a plot destined for a new building-regs compliant house, and blinged it up to a passiv house, Fred will have reduced the U by about 0.1W/m2K. So Jo has done a whole lot more for society and the UK building stock than Fred did.

    Edit: my point is, GBF should welcome and encourage Joe as well as Fred.
  19.  
    My mission in life (as I do what I really should be doing!) is to make as many people as possible aware of the requirements of Part L with regard to refurb. So many people I meet have refurbed their house to a non-compliant level, and without applying for a Bldg Notice, simply because they did not know there was anything to comply with. In many, many such cases they would have refurbed to a higher spec if they had known that was (a) legally required and (b) desirable.

    The insulation in my house will probably not be finished before I die, so I balance that by under-heating it. (I think that*) We all have Climate Change to focus our minds!

    *acknowledging that some don't agree that we are causing/contributing to it.
    • CommentAuthorKenny_M
    • CommentTimeSep 26th 2019
     
    Posted By: GreenPaddyIf your "Joe Bloggs" fires in a load of insulation in his loft, with an old style felt under his slates, and blocks all the eaves ventilation, he may come back in a few years to find a load of rotting roof timbers...and that's about the simplest of possible home improvements.


    To be fair, that is also possible if it was done by a 'professional', and I have never heard of anyone getting a building warrant for loft insulation. I had a company do it for me in another house a few years ago and they didn't apply for one. Before deciding to do my extension renovation myself I had a council approved 'truster trader' around who suggested putting underfloor heating in by cutting a raggle into a un-insulated slab. I could barely answer him I was so taken aback, and I'm the amateur.

    Another builder wanted to just cut away the wall to fit the doors and leave the timber post sitting on a corner dwarf wall that would . My original drawings that went to building control had this design on it and they did not flag anything up, I had to take it into my own hands along with advice on here, which prompted me revising the submitted drawing to a full length post. My warrant is now approved but they haven't asked me for structural calculations, even thought the post is double the length (I have done this to satisfy myself but they haven't requested them).

    I agree that 'if' you get a knowledgeable, helpful BCO, that the cost of the warrant is good value. To be honest I thinks it good value even just for the administrative aspect and the issuing of the warrant, but I think there has to be a judgement made on when it is needed, and if I make that judgement I accept that I am responsible if it goes wrong.

    Just to be clear, I am not advocating cutting corners or avoiding BC for the sake of it. I've obtained a warrant for my new doors and committed to 0.7u when I only need 1.6 for approval, I just think we have to be pragmatic when dealing with existing housing stock, especially very old properties.
    •  
      CommentAuthordjh
    • CommentTimeSep 26th 2019
     
    Posted By: WillInAberdeenIf Jo/Joe Bloggs adds 200mm of loft insulation where there was none, because that's how much is feasible or economic in their situation

    I don't think feasibility is a reasonable argument there. Simply look for a better performing insulation. And it isn't 'economic in their situation' it's economic according to the stated criteria.

    IMHO, if you look at a property and don't think you can sensibly improve it beyond building regs, then that's a very good reason not to buy the property, just like if it was in a flood zone or by a motorway. Leave it for somebody else and find another. If nobody else wants it, then knock it down and start again. With the only exception being buildings that are 'important' for some reason.
  22.  
    Posted By: djh
    Posted By: WillInAberdeenIf Jo/Joe Bloggs adds 200mm of loft insulation where there was none, because that's how much is feasible or economic in their situation

    I don't think feasibility is a reasonable argument there. Simply look for a better performing insulation. And it isn't 'economic in their situation' it's economic according to the stated criteria.

    IMHO, if you look at a property and don't think you can sensibly improve it beyond building regs, then that's a very good reason not to buy the property, just like if it was in a flood zone or by a motorway. Leave it for somebody else and find another. If nobody else wants it, then knock it down and start again. With the only exception being buildings that are 'important' for some reason.


    Many people do hope "somebody else" will sort out the existing housing stock, or hope somebody might "knock it down" and replace it with shiny new houses. But as I understand it, that isn't actually happening very much - or not nearly fast enough.

    So we need many more folk like modernvictorian (and others, and me) to make all the changes that are feasible and economic in our existing 19th/20th century houses, which are going to be standing for a long while yet.

    MV could "simply look for a better performing insulation", and aerogel was suggested as an improvement on phenolic, but he/she may find thats not economic in their situation.

    An example from my previous house was a partly floored attic, accessed through a low doorway. I put 2x200mm layers of wool in the unfloored bit, except under the eaves where only 1x200mm layer would feasibly fit (ventilation issue as mentioned above).

    I prodded and squished 200mm wool under all of the floored area. The access didn't allow rigid insulation and it needed to be breathable. I could have increased this to 300mm by hiring someone to rip the floor out, raise the doorway height, add a step up, then replace the floor on new joists, but that was uneconomic to achieve the extra 100mm of insulation.

    IMO that was entirely compliant with building standards, and the building standards people were quite happy when they came round to look at something else in that room.
    • CommentAuthorKenny_M
    • CommentTimeSep 26th 2019
     
    Posted By: djhLeave it for somebody else and find another.


    I don't understand how that would help. The previous (very wealthy) owner of my house, just left the 30 year old boiler on full blast, without a shred of insulation to be found anywhere including the attic, polycarbonate roof-lights, metal framed doors and single glazing throughout. I can't understand how that would be a better scenario than getting close to, but not quite meeting the modern building regs. I'd estimate my energy consumption is likely to be a 1/3rd of the previous owner.
  24.  
    Thanks for bringing a lot of relevant points to my attention here. I am sensing that I will be sat in some sort of Building Regs grey area whereby I may or may not be granted some leniency on the basis of the age of the house. The comments from @Kenny_M and Will are ringing true for me and I will be upfront in saying that I am looking for the best compromises between efficiency/cost/retaining the charm and character of the original building. It would be a different story if I was starting from scratch with a new build.
    •  
      CommentAuthordjh
    • CommentTimeSep 26th 2019
     
    Partly sorting out houses won't solve the climate crisis.
    • CommentAuthorJeff B
    • CommentTimeSep 27th 2019 edited
     
    <blockquote><cite>Posted By: modernvictorian</cite>I previously read through the thread on Bauwer Insulated plaster/render and actually it was this that persuaded me that it could be suitable for my project. I have to admit to not being familiar with Building Regs and when they would kick in. Also have to admit to being a bit surprised that I would need to achieve a U value of 0.3W/m2K. It seems like a tall order for a solid wall and surely something is better than nothing?! But the rules are the rules I guess.

    I have been reading about Spacetherm. I will have a look at phenolic foam also.</blockquote>

    Modern Victorian - have you considered Sempatap?

    https://www.mgcltd.co.uk/sempatap-thermal/

    I have never used it myself but looks useful in places where internal dimensions are critical. I am considering it for a shower room in our dormer bungalow where we have a curved ceiling (skeiling) situation with very little clearance above the shower enclosure.Won't comply with Building Regs as the U value is not brilliant but has to be better than nothing, if only to avoid condensation on the ceiling?
  27.  
    A few thoughts re 'thinner solutions':

    Proctors do 10mm Spacetherm (Aerogel) bonded to 3mm magnesium oxide board, with a combined thermal resistance of 0.676m2K/W. 13mm thick. One merchant charges about £55/ 600 x 1200mm board.

    Sempatap thermal resistance (at 10mm): 0.194m2K/W. 10mm thick

    12mm PIR + 9.5mm plasterboard. Thermal resistance combined: 0.5516: 21.5mm thick
    • CommentAuthorKenny_M
    • CommentTimeSep 27th 2019
     
    Something to think about, but I read some research done by Historic Scotland, who found that the walls in period had far better measured u values than the theoretical or modelled results. Not good by modern standards, but for example where some walls were modelled to be say 2.5, they were actually closer to 1. This was often down to the fact that what are presumed to be solid walls are usually in practice two skins with a filled cavity, and depending what was thrown in the cavity the u values would vary wildly. Often the wall itself isn't too bad, but air is coming through the suspended floor and up the back of the lath and plaster, which makes the u value of the wall pretty redundant.

    I only mention this because treating the walls in period houses can be really disruptive and difficult, and there might be bigger and quicker wins from other things while you think about the walls. If you have single glazed windows, or lots of air leaks for example in sash and case windows or through suspended floors. If you have a fire or stove, with winter coming in they provide an easy way to check for leaks as the fire will pull cold air in around all the gaps and make leaks easy to find. Also, if you have big old fashioned windows they might have a u value of 6 or worse, and even tightly fitted secondary glazing would dramatically reduce this if there is an issue replacing with DG/TG.

    You may already have done/considered all of this, and if so just ignore me! :)
  29.  
    Of course not, this is useful stuff! I hadn't considered about the air leaks through the floor but that sounds very feasible. I think I will end up going back to brick as the plaster seems to be blown in many places so there is a good opportunity to sort some of these issues out. In all honesty I can't see myself going for EWI as I would only do the back of the house (so as not to ruin the pretty face!) and given the kitchen extension at the back there won't be much wall left to insulate. Which leaves me finding the best internal solution.

    I will take look at Sempatap also. The U value looks pretty good for 10mm?

    I am not hearing anyone encouraging me in the direction of the Bauwer plaster :-)

    From everything I have read it seems like an old solid wall needs to be kept as dry as possible so any solution needs to be breathable. There is also some interesting findings about solid walls and how damp affects the U-values. I am really buying into the theory that dryer = warmer.

    The windows were replaced with really awful aluminium DG which are at the end of their life so the whole lot needs ripping out and replacing. Don't know how they got away with the aluminium in a conservation area. My heart bleeds for those original sashes. I have a quote for new double glazed sashes. Again this seemed like a good compromise as triple glazing will be very difficult to fit in a box sash frame and would look very odd I feel.

    I don't have any ideas about the suspended floor and how to draught-proof. I really want to put in UFH between the joists to generate a constant heat source (also good for keeping the walls dry) so I assuming that the floor insulation would be part of this installation? But really haven't looked very far into this.

    No fire to test for draughts I'm afraid. Just a gas imitation. As I mentioned most of the nicer period features are long gone.
    •  
      CommentAuthordjh
    • CommentTimeSep 27th 2019
     
    Posted By: modernvictorianThe U value looks pretty good for 10mm?

    About the same as a single-glazed window that's half as thick? I wouldn't call that especially good.

    I would suggest not doing anything in a hurry. I suspect you have a lot to learn and that your ideas will change quite rapidly over time.

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