Insulation on a period property

[Lithgae]

Hi all,
First post! About one year ago, we moved into a detached Sandstone house, in Linlithgow, central Scotland, built at some point in the 1800's. Not sure of exact date of construction, the surveyor said 1885, but I suspect that was a guess based on the Victorian bay window, but a closer inspection shows that the bay appears to have been added (stone is very slightly different), and if you take the bay away it has a very symmetrical Georgian look. Looking at some of the old records of the two I think it may have been first built around 1820, but could be on the site of an older property, possibly a cottage.

Much of the time since I have been dealing with various problems, reopening painted shut windows and shutters, some damp problems, getting some of the stonework on the exterior sorted, chimney rebuilt etc.

Anyway, the point of the post was to open up a discussion about insulation. I am planning on getting the cement render that has been applied to the exterior on the rear and sides taken off and depending on the state of the stonework underneath possibly re-render with something more appropriate than cement. If I re-render I am considering external wall insulation and was looking at a cork based insulated render. Discussing with some people who are very knowledgable about insulation and green building, they suggested rendering over EPS boards, stating that these are breathable or "vapour open". I am cautious about this because it doesn't seem to fit with what I know about old buildings, but I am also keeping an open mind.

Anyone on here used EPS on old houses, or have any thoughts about insulation?

 

[MatthewC]

Hi Lithgae, welcome to the forum.

I have no experience in the use of cork based insulated render or expanded polystyrene but I cannot believe that the latter is breathable.

However, I wonder if your building is listed? I'm sure the rules are different in Scotland but, since so many buildings are externally rendered in Scotland, I would have expected that there must be some sort of official guidance from conservation officers etc.

Are you going to insulate the loft? I have Thermafleece on the loft joists and that is mosr effective.

Best of luck

Matthew

 

[Lithgae]

Thanks Matthew.

The building is not listed, but it is in a conservation area, so while I could re-render using an insulated render to a similar depth to the current render without planning permission, if I was to put it on thick (as you would obviously want to with insulation), and it thus make the exterior look different, then I would need a householder application.

A lot of properties are harled (pebbledash I think its called in England) traditionally here, to protect the stone from the elements. However, its cement based (as opposed to lime) on my walls so I suspect it has been put on in the eighties. What the planning office would want to understand is how it would change the look of the building and this would be tricky particularly where it would be very visible towards the apex of the roof. I think the best way would probably be to taper the insulation off as it approaches the front of the house and the roof.

I think the thing about the word breathable is that materials don't go from a binary breathable to not breathable, obviously some are more breathable than others, but the difficult question is how breathable a material needs to be to match the characteristics of lime mortar and stone wall. The other thing is what you cover EPS with as it would have to be rendered, and how breathable that would be.

I am kind of trying to serve two masters here, attempting to retain the characteristics of the building as much as possible, and at the same time make a more energy efficient home, so there is a bit of a balancing act.

 

[Zebra]

I have woodfibre external wall insulation, 60-100mm thick over period timber frame, with a proprietary lime render. I don't know whether I can tell you anything useful about it. Woodwool is also an option. Both are less effective insulators but more breathable than polystyrene, I believe. I guess it depends how breathable you need it to be. Does the house have damp walls currently, from any source other than condensation, I mean?
I very much understand your approach of wishing to retain character while insulating as well as possible. I suppose in that regard you are lucky that your current render is of no historical value, as indeed mine wasn't.
The tricky bits are reveals, gables and eaves. If you are replacing other building elements like roof and windows then it's easier, otherwise creative solutions must be found!

 

[Tony.]

Can’t help, but visited a few years ago to the Palace!

Same age house, I’m whinstone in NE Fife, done the internal route of insulation but good luck with the external, do you have to watch out for window cills, down pipes etc as I recently saw a block of flats covered in EWI and they made no allowance for this apart from cutting in recesses into the insulation-

 

[Lithgae]

Thanks Zebra and Tony,
If I do the render, or any type of insulation, it would need finish near the front as there is Ashlar block sandstone on the front that would be a crime to cover with render, and in fact would literally be a crime as it is a conservation area. Fortunately there is a downpipe near the front that would hide the edge, but I would have to get lead flashing to edge it off and cover the join at the seam.

No damp issues higher up, not withstanding the leaking chimney. Some ground level issues so it would need to be breathable.

Bigger problem right now is the chimney rebuild which is turning into a disaster. Might put up a separate post about that.

 

[fernicarry]

they made no allowance for this apart from cutting in recesses

A group of houses up the back of Helensburgh just had the full EWI treatment, but they didn't bother moving the gas meter boxes so they now sit nicely recessed into the wall...

Lithgae, how are the internal faces of your external walls finished? If you're like us you'll have lath and plaster carried on studs 'dooked' (sp?) into the external walls. This allows air circulation up the inner face of the external wall to take away any moisture which might penetrate the full thickness of the wall. This air circulation would surely undo any of the benefits of EWI would it not?

 

[GPHouse]

Hi

I saw a demo of EcoCork at Mike Wye in Devon - its a cork based external render you plaster on. Really interesting stuff and its been about on the continent for some time.

Essentially its superlightweight insulating render, which has a high thermal efficiency. It finishes nicely but ther eis a bit of a sponginess tot he final finsh if you accidentally run into the wall.

Definitely worth having a look and it was really easy to apply.

G

 

[skier-hughes]

It finishes nicely but there is a bit of a sponginess tot he final finish if you accidentally run into the wall.

G

If I run into a wall a bit of sponginess is a benefit.... you appear to be saying it isn't

 

[Tony.]

they made no allowance for this apart from cutting in recesses

A group of houses up the back of Helensburgh just had the full EWI treatment, but they didn't bother moving the gas meter boxes so they now sit nicely recessed into the wall...

Lithgae, how are the internal faces of your external walls finished? If you're like us you'll have lath and plaster carried on studs 'dooked' (sp?) into the external walls. This allows air circulation up the inner face of the external wall to take away any moisture which might penetrate the full thickness of the wall. This air circulation would surely undo any of the benefits of EWI would it not?

Passed the block I mentioned

They didn’t move the door entry system either, the only thing they did seem to move was the sat dishes!!
Flats near tannadice when I go to the football

 

[Lithgae]

Sorry for the delay in replying, combination of me not getting notifications and as a new user my posts are taking a while to get moderated.

Fernicarry - the internal walls appear to be a mix. A lot of them have had gypsum plasterboard added, but I suspect some of the rooms are lath and plaster, but in either case there is a gap at the back and although they back isn't usually deliberately ventilated the inevitable drafts up here could be an issue. From what I can see where I have re-opened up one of the fireplaces it actually looks as though there was originally lime plaster straight on to the wall, then lath and plaster added later, then gypsum plasterboard used when the fireplace was closed up.

GPHouse - Ecocork I think is similar to the other products I was looking at, Bauwer Lite and Diathonite Evolution, although I think both of these have a lower thermal conductivity than EcoCork.

Diathonite appears to be the best insulator of all of the breathable/natural insulated renders on the market, but I have found it difficult to find anyone in the area with any experience of these types of render. There are also a few practical problems with applying it, not least planning permission, the fact that I would need to either extend out the coping stones, or fit lead flashing at the roof level which would be very expensive, and might look rubbish - which in turn would be a planning problem in a conservation area. There is also the the fact that I would probably be spending around £20k to get it all done, and I would still have an uninsulated north facing where even if I was enough of a savage to want to render over the Georgian Ashlar sandstone front of the house, I wouldn't get planning anyway.

I think that these natural insulated renders could be ideal for period houses that were already traditionally rendered all over, but for mine I am not sure it would ever look right. I've decided for now just to get the 1980's cement render off the sides and the back, and get it pointed up. I am going to take my time and think it through. It might be better to spend the money on internal insulation, focusing on the rooms that are used most.

 

[MikeG]

Just a note to the previous....

Insulating renders may have a role, but they are going to make very little difference to the thermal performance of the building. I looked into these before, and found that the best have approximately the same R value as a sheet of plywood. Render is applied to the wall at a maximum thickness of 25 to 30mm. Imagine the effect of a sheet of 1" ply on the outside of a wall, and how much or little difference that would make internally. The measurable effects would be negligible.

 

[noj]

Imagine the effect of a sheet of 1" ply on the outside of a wall, and how much or little difference that would make internally. The measurable effects would be negligible.

It all depends on the wall - for the OP with stone walls I guess it probably wouldn't be significant, added to our cottage it'd increase the amount of solid material by around 50% and I'm sure would be measurable (most walls are 1" lath and plaster inside, approx 1" weatherboard on the outside or, on the most exposed bit, lath/plaster in, lath/render out)

In this case I'd tend towards keeping the render to the original thickness (albeit more insulating) for appearance's sake and concentrate on draft proofing, loft insulation and an efficient heat source

 

[GPHouse]

The Ecocork is about 40-50mm and the figures are between 10 and 35% improvement - wile not amazing.... its still breathable, waterproof and an improvement on nothing at all!

 

[Lithgae]

Hi,
I don't agree that it is equivalent to a sheet of plywood. A quick google and Ply has a thermal conductivity of around 0.13, Ecocork is not much better than that so that might be the reference point, but Diathonite evolution, the best performing of the renders I have found is 0.045 W/mK - that's not far off EPS board. 25mm of diathonite would bring a sandstone wall with u value of 2.3, down to 1.02, that would more than half the heat loss from the wall, and ~50mm and you are getting to around 0.5. That's pretty good when you consider that new build minimum is 0.3.

I think the question really is whether it would be worth it compared to internal insulation, and I am not convinced it would be, given the complications of my situation where I can't render the front, and a flashing would need to be applied at the top etc, probably in expensive lead to meet planning. I also spoke to someone at the Scottish Lime Centre, and their only real concern is whether it would stand up to the Scottish climate, wind driven rain etc!