Masons arrived today to start work on the sandstone chimney which is being completely rebuilt. I've been quoted £6k for this work, but it needs to be done as there is water ingress and years of cement patches that are not going to get any better. Part of that cost is £1200 for scaffolding, so while the scaffold is up I really need to make a decision on what to do with the render on that gable.

It looks like about £1k to remove the existing render which is cement based. The base coat is fairly solidly stuck on, but the outer roughcast is hanging off and needs to be removed. Cement render on sandstone is also known to prevent the natural breathing of the walls, leaving them damp and conductive, which is another reason for getting it off.

Option 1: Is to simply tidy and repoint the wall for which he has estimated £2,400. So the cheapest option available.

Option 2: Is to remove the cement and re-render in lime, and this probably sets me back about £3500 in total. I don’t really see the point of this, unless of course the original stone below is in too bad a condition to leave exposed.

None of this improves the insulation of the wall, which is why I have been looking into insulated render and asking about this on the other threads and leads me to option 3:

Option 3: Diathonite Evolution seems to have the best thermal conductivity (0.045) of the available breathable, insulated renders. 50mm of this stuff would give me a decent improvement but that is about as thick as I could make it for various reasons discussed on other threads. However, the main problem with this stuff is getting someone to do it, and although I have had a quote of around £4500 for that gable, the nearest contractor is hundreds of miles away and with travel/subsidence this quote would get higher, and I have a feeling it would need a lead flashing along the top which is probably going to mean another grand or so.

So, in summary on top of the work that needs to be done anyway, I am probably looking at a minimum of £2k, and probably more likely £3-4 to insulate one gable wall. When I consider that of the 5 rooms that are on this gable end, 2 are spare bedrooms that are rarely used and so rarely heated, one is a bedroom that is never heated to more than 10-15 degrees, and only the two downstairs ones are used with any regularity - which means some evenings and weekends, I am starting to wonder if I would be better insulating the rooms that are actually used with internal insulation. The internal area of the walls of these two rooms are around 8m2.

I haven't really researched internal insulation yet. I may be limited to around 50mm internally due to internal features. Old house so it needs to be breathable and I have read that aerogel is breathable and can go on the hard, but this is crazy expensive.

Sorry for the long ramble, but wondered if anyone has experience of breathable internal insulation or has a view on which is the better way to go?

One important point is that due to conservation area rules I can never cover the exterior of the house, and this is the north facing wall, so all the north facing rooms would still need to be insulated internally on one wall.

The suppliers say that any good plasterer could use it, but most that I speak to don't seem very keen. I think that the traditional lime based guys are understandably cautious of using non traditional materials, while the modern guys are only used to using sand and cement - and some of them look at me like I am crazy when I say that the wall needs to "breathe" :)

I posted on the plasterers forum to see if anyone had used Diathonite/Bauwer/Baumit etc, and there was only one person who knew someone who had used and said it was a nightmare to work with and a poor finish.

Even better, Graphite EPS is 0.032W/mK.

+2

EPS has approximately the same vapour permiability as wood (as does PIR without foil facings).

What is WVT? (wikipedia doesn't know)

The plannng department has no say or interest in EPS or not. All they care about is the appearance of whatever covers it.

The 'traditional' lime guys around me are very happy to experiment and use new materials, because they have to adapt modern materials to a whole host of different traditional situations (not many are too interested in mixing in cow manure or ox blood!).

In my view EPS is vapour open but foam sheets like PIR without foil are not.

<blockquote><cite>Posted By: Kenny_M</cite>EPS is somewhere in the middle</blockquote>
True - and variable in different reports. But def OK in say a new 'breathable' wall build-up, which is likely to include for instance OSB, which is equally 'middle and variable'.

Anyway it's a world away from cement render, which is not only highly absorbent of liquid water via its network of capillary cracks, but also usually (but not always) more or less impermeable against re-evaporation.

If conservation advice fails to mention EPS as suitable facing, that's prob more to do with purist ideology, and I'll bet there's no alternative insulation type that is recommended.

It's true that EWI does create detailing problems that can be unsightly anywhere, and utterly verboten in Listed/Conservation work. So yes, how would you treat the corners, if only doing an isolated gable end? Not to say neat solutions can't be found.

But yes again, 'thick' render like Diathonite has a chance to be craftily tapered off to the verge and to leave those corner stones exposed on the gable face (tho creates an insulation weak point), even softly tapering to nothing if the corner stones are flush, a bit like http://www.repointer58.com/siteimages/photo011%20(640x480).jpg (but in reverse - can't believe I can't find a gd pic).

Mind you, removal of cement render and knowlegeably done repointing will make that gable a lot drier, after a couple of summers, and therefore less lossy, less mould-prone.

Worth a close study of Permitted Development rules
http://www.legislation.gov.uk/uksi/2015/596/pdfs/uksi_20150596_en.pdf (see Part 1 on p13, and read all the rest in that light)
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/606669/170405_Householder_Technical_Guidance__-April_2017_FINAL.pdf (see esp p33)

A lot depends on whether your LA classes EWI as 'cladding' or 'over-cladding', or as simply replacement of existing render.

EPS has been used for over 30 years in Germany and there are studies that show no degradation over that time. There are also studies that show that EPS performs better below ground that the often quoted XPS needed for below ground applications.

There is no reason why EPS has to be installed with a square edge. It would be an easy job to taper or round off the edges either once the ESP is up and before rendering or before placing the edge sheet on the wall.

I have insulated a stone / rubble wall with EPS without problems. The stone work (basalt rock) was not too flat and the choice was to render flat first or use a thicker layer of adhesive to take up the difference. I calculated that a thicker amount of adhesive would be cheaper. The method used was to put a thick line of adhesive top and bottom of the sheets with 4 good dollops in the middle, the sheet was then pressed onto the wall as far as it would go or to give a reasonable fit to the adjacent sheet. Once the wall was finished the whole lot was sanded (with the tool made for the purpose) to take out any protruding edges prior to rendering. This worked well, the insulated wall is still not flat but has gentle undulations when you look down the wall. (it is 36M long).

Apart form the obvious the reason I insulated the wall (north facing) was because I have tenants in the house and one room, which they did not use much and only heated when needed was getting black mould all over the wall. They washed the wall with bleach but 2 weeks later the mould was back. 100mm of EPS insulation on the outside fixed the problem! It is now the 3rd winter with the insulation in place and there have been no problems. In fact I only insulated the problem area to start with and this solved the problem so last summer I insulated the rest of the building to match.

Posted By: Peter_in_HungaryEPS has been used for over 30 years in Germany and there are studies that show no degradation over that time.

I'm in France, and have 50mm EPS EWI on a 1983 construction.
Got a chance to examine it in detail 2 yrs ago during installation of new windows, looked as good as new.
It's true I have a few minor repairs (cosmetic) to address on the rendering in places...
(in fact it is not rendering, but extremely hard cement board, with a sort of Artex facade paint).

gg

Posted By: Kenny_MI'm not able to see the pic you posted - it just keep bringing up an error. Was interested to see this if you don't mind posting again.

I couldn't get it to 'underline' the whole - just copy/paste it into a new tab.

yeurrk !

perhaps it was the bedroom wall of the neighbouring property forcibly demolished in the meantime...


gg

djh - its the same here, but being in a conservation area changes everything. As far as I am aware there is no document as such covering what can and can't be done in this area. I've asked about this before and they just direct you towards submitting a householder application. What I have been told is that like for like repairs are fine, but anything that involves a change in materials being used requires an application. I know for example that they won't approve PVC frames for double glazing, and they are fussy about the type of glass that is used. I agree that with EWI its more how it looks that they will be concerned with. I'd have to do some drawings to convince them.

Tom - I see the pic now. Yes, this is what I was thinking about, in reverse as you say.

Peter - Interesting to know that you insulated a stone built house with EPS. I don't know how the permeability of Basalt compares to sandstone, although from the bits of the old render I have taken off so far it looks like my wall on the side is actually a mix of sandstone and whinstone. I think in at the time of construction Ashlar Sandstone would have been very expensive and only put on the front, with the sides made from cheaper rough cuts of local stone.

I don't see the weak point in the insulation being a big problem because where it tapers off to the side will be after the point where the uninsulated front wall begins , as they are around 600mm thick. Where it tapers off at the top will be at the roof, so also beyond the point of the heated part of the inside wall. On the gable I am talking about there is a drainpipe which would help to disguise the tapered end. However, on the other gable I have a bigger problem, the fact that this wall borders the next property, so any protruding insulation would be protruding into their space. They are pretty reasonable so would probably be ok, but its another consideration.

There remains the issue that the coldest wall (north facing) will be the one I can't insulate from the outside and I would have thought this would then become a condensation risk. I can of course insulate that wall from the inside, but then I am back to thinking if I am going to insulate one wall from the inside, would I be as well to just insulate all the walls on the inside and have a uniform insulation in the walls.

The other thing I keep thinking about is the chimney stack on the gable. 3 of the 4 flues are unused, so it means that I would be insulating the outside and a ventilated cavity in the middle.

I think all of this needs a bit of planning and I might be better not to jump in now unprepared just because I have a scaffold up. It might be good, as Tom says to let the wall breathe for a bit after getting the cement off, and ensure all the dampness issues are resolved before doing anything more. I actually think the leaky chimney has been the main problem but it will be some time after this is fixed before I can confirm that. Given the limited funds I have available its probably also better to direct these towards CWI in the extension, new condensing boiler, upgrading the glazing etc.

This discussion has given me plenty to think about so thanks all for your comments.

deleted - mis-posted

Posted By: fostertomafter render removal, essentially incl gd repointing, if it's to be left bare.

If it is to be left bare for any length of time and it matches the front then it might be the devils own job to get the CO to agree to re-rendering. Get agreement to re-render in writing before the works start.