Insulating a pebbledash solid wall and damp concerns

[Adsibob]

On 28/01/2022 at 10:02, Ben Weston said:

though we are looking at an injected DPC as part of our renovation works)

Stay well clear of this nonsense. It’s a complete con. Rising damp is pretty much a myth invented by the damp proofing industry to make money. Damp is obviously a real problem in a country as humid as the UK but it is rarely solved by chemical injection.

[Adsibob]

What you are describing is similar to the issues I faced with my 1930s según that was covered with pebbledash. I got a RICS surveyor who designed a system where externally the pebbledash was replaced by EWI covered which was then covered in a silicone based render, and internally we used a Tyvek breathable membrane on the wall, plus a void of air to let it breathe. We only did the internal detail at ground floor because it was only ground floor that the walls were a bit damp (with one wall in particular being very damp).

We also introduced French drains externally. 

[Ben Weston]

8 hours ago, Adsibob said:

What you are describing is similar to the issues I faced with my 1930s según that was covered with pebbledash. I got a RICS surveyor who designed a system where externally the pebbledash was replaced by EWI covered which was then covered in a silicone based render, and internally we used a Tyvek breathable membrane on the wall, plus a void of air to let it breathe. We only did the internal detail at ground floor because it was only ground floor that the walls were a bit damp (with one wall in particular being very damp).

We also introduced French drains externally. 

 

Thanks Adsibob. Injected DPC already ruled out – realised quite quickly this is one of those 'old wives tales' with little substance.

 

Your approach sounds similar to the one I'm arriving at, though I'm currently looking at K Lime as the outer render. I'm interested in the air void you created. Presumably this had to be vented somehow? 

 

I'm going to look into EPS and modified lime render on the suggestion of Simon (thanks Simon). The house is surrounded by trees, so not exposed at all, which might make EPS viable. If we can get away with this, we'd have the budget to over-rate it to 200mm-ish and apply it around the whole house (including the new extension with cavity walls) which would result in a really well insulated house.

 

So today's research is whether the following system is viable:

 

K Lime Render > 200mm(ish) EPS > Vapour-Permeable Adhesive > Solid Wall > Traditional Lime Render

 

I realise that, just as important, is how the details are finished and how it terminates in the roof. This needs more research but it seems like the base should be XPS down to the bottom of the land drain and about 6 inches above to the bottom of the rail the EPS sits on.

[SimonD]

1 hour ago, Ben Weston said:

seems like the base should be XPS down to the bottom of the land drain and about 6 inches above to the bottom of the rail the EPS sits on.

 

This is the go to for plinth insulation although you can use EPS with no problem as EPS performs fine sub grade and even when it's wet. Saves a few quid on the project.

[Adsibob]

3 hours ago, Ben Weston said:

 

Thanks Adsibob. Injected DPC already ruled out – realised quite quickly this is one of those 'old wives tales' with little substance.

 

Your approach sounds similar to the one I'm arriving at, though I'm currently looking at K Lime as the outer render. I'm interested in the air void you created. Presumably this had to be vented somehow? 

I'm not entirely sure. The principle we used is that the inside of the house was breathable to that void, but the outside to the void was effectively sealed. This would allow any remaining damp to dry from the inside. The RICS surveyor liaised closely with the Tyvek technical department who carried out an interstitial condensation risk assessment and concluded this was the best solution. We have MVHR as well, and that was taken into account too.

 

3 hours ago, Ben Weston said:

 

I'm going to look into EPS and modified lime render on the suggestion of Simon (thanks Simon). The house is surrounded by trees, so not exposed at all, which might make EPS viable. If we can get away with this, we'd have the budget to over-rate it to 200mm-ish and apply it around the whole house (including the new extension with cavity walls) which would result in a really well insulated house.

 

So today's research is whether the following system is viable:

 

K Lime Render > 200mm(ish) EPS > Vapour-Permeable Adhesive > Solid Wall > Traditional Lime Render

 

I realise that, just as important, is how the details are finished and how it terminates in the roof. This needs more research but it seems like the base should be XPS down to the bottom of the land drain and about 6 inches above to the bottom of the rail the EPS sits on.

I did ask the RICS surveyor to consider lime render, as I had heard good things, but for some reason he ruled it out. I would recommend you get advice from a RICS surveyor who has expertise in designing these kinds of systems. Each house is unique and has it's unique challenges. There is no one size fits all, and ultimately when one is refurbing a house that is so old (and in my case, a bit damp) there is no perfect solution, just the best solution. I can recommend you my guy if you PM me, but I'm not sure where you are based.

[hb1982]

I believe typically EWI with 100mm EPS insulation can achieve around 0.30 W/m2K U-Value, a big improvement from existing 9 inch solid wall.

 

200mm EPS is not the standard. Although it improve the thermal performance to around 0.15 W/m2K (or lower?), i.e. around 3W per sqm (@ 20 degC temperature difference) in real term, it makes no practical difference. You are, however, introduce further risk of thicker / heavier build-up on existing masonry construction; much bigger and longer screws; non-typical details; bespoke windows cill... 

 

I would suggest to focus on the right materials which you have done so far already and stick with the industry norms. 

Edited February 2, 2022 by hb1982

[Ben Weston]

 

38 minutes ago, hb1982 said:

200mm EPS is not the standard. Although it improve the thermal performance to around 0.15 W/m2K (or lower?), i.e. around 3W per sqm (@ 20 degC temperature difference) in real term, it makes no practical difference. You are, however, introduce further risk of thicker / heavier build-up on existing masonry construction; much bigger and longer screws; non-typical details; bespoke windows cill...

 

Yes, having looked into it a bit more, I think 200mm would be overkill. I think there's scope to go more than 100mm especially as there's relatively little cost difference in doing so. Perhaps 130mm or something like that? That, I think, would still allow fairly 'standard' decoration.

 

2 hours ago, Adsibob said:

I did ask the RICS surveyor to consider lime render, as I had heard good things, but for some reason he ruled it out. I would recommend you get advice from a RICS surveyor who has expertise in designing these kinds of systems. Each house is unique and has it's unique challenges. There is no one size fits all, and ultimately when one is refurbing a house that is so old (and in my case, a bit damp) there is no perfect solution, just the best solution. I can recommend you my guy if you PM me, but I'm not sure where you are based.

 

That's very kind, thank you. To be honest, I've spoken to quite a few RICS/RIBA-certified people now who all give me slightly different advice. I'm sure there's more than one right answer, of course! At this stage, I just want to understand as much as possible myself so that I have confidence in whatever route we eventually choose. 

 

41 minutes ago, hb1982 said:

I would suggest to focus on the right materials which you have done so far already and stick with the industry norms. 

 

Thanks. I think I'm satisfied that EPS will provide enough permeability for what we need so long as we render in lime internally and use a lime, or lime-like, render externally. Still not sure which external render to go for but we can come back to that. The main thing is establishing how much is being added to the walls so our architect can sort the roof on the working plans.

 

Thanks all for your very detailed help as always.

[Ben Weston]

3 hours ago, Adsibob said:

We have MVHR as well, and that was taken into account too.

 

Missed this. We're looking at MVHR too.

[Roger440]

On 01/02/2022 at 17:17, Ben Weston said:

 

He thought a land drain around the building might be a good idea so long as it didn't dry out the clay the house is sitting on too much and lead to subsidence. The reason for us considering this is that the cottage sits in a 'dip', the internal and external floor levels are the same, and it's been known to flood in the street.

 

 

 

Unless you have a specific issue with water around the base, id strongly advise against this. The risk is exactly as you say. Why take the risk if its not needed.

 

I pondered the same early on, before i started inside. Elected not to. Most of my problems were caused by internal stuff. Base of wall is as dry as a dry thing..

 

As always with old stuff like this, it will have reached some kind of equilibrium. Mess with it at your peril.

[Roger440]

On 01/02/2022 at 18:16, SimonD said:

 

Yes, a lot of words of caution here. The buildup you have linked to uses Secil Reabilita CAL AC as the render on Schneider woodfibre boards. However, if you look at the technical data sheet for the Reabilita, it is a finishing render for SecilTek's Cork EWI system. There is no mention of suitability for use on a woodfibre board. If you go to the Scheider woodfibre page and download their European Technical Assessment document for alternative renders on their woodfibre boards installed on masonry substrates, Reabilita CAL AC is not present. https://www.schneider-holz.com/en/service/the-plus-in-service-accessories/downloads/download/eta-15-0731-different-plaster-manufacturers-on-mineral-substrates/ Also, the Reabilita Cal RB listed in the buildup by Ty Mawr is not given to be suitable as a render basecoat on Woodfibre by SecilTek - it's for masonry substrates.

 

My experience has been that Ty Mawr have changed the finishing render they use on this system but other than a registered LABC detail, there doesn't appear to be any technical assessment as to the suitability of the buildup.

 

You will also find that there is scant information on the whole ewi buildup by Ty Mawr; missing are, for example, reveal details, corner beads, stop beads, mesh detailing around window and door openings etc. If you go to Schneider's website, the technical details can be found for their render system, but given that it is totally different from the one Ty Mawr are proposing, it is unlikely to be in line with Reabilita CAL AC/Cal RB. https://www.schneider-holz.com/en/service/the-plus-in-service-accessories/downloads/download/installation-guidelines-etics/ . As this is going to be a thin-coat render system, there is no way you want to be installing it without all these requisite details and reinforcements. In addition, the layers given by Ty Mawr for the Reabilita renders, take it to 15mm, which is not suitable for woodfibre, which uses lighter weight thin coater render systems at approx 8mm.

 

The only pure lime render that I'm aware of that is technically developed specifically for woodfibre EWI is by Lime Green - https://www.lime-green.co.uk/warmshell/warmshell-exterior

 

I could of course be wrong here and the best way to test it is by asking Ty Mawr for the technical assessment and approval for the use of Reabilita CAL AC/ Cal RB on woodfibre and for their documentation on the system buildup detailing and specific installation instructions. Also, is there any warranty with their system?

 

What thickness ewi is your AT suggesting?

 

Interesting thoughts on the ty -mwar EWI. Do you have any thoughts on their interior systems?

[Roger440]

19 hours ago, Adsibob said:

What you are describing is similar to the issues I faced with my 1930s según that was covered with pebbledash. I got a RICS surveyor who designed a system where externally the pebbledash was replaced by EWI covered which was then covered in a silicone based render, and internally we used a Tyvek breathable membrane on the wall, plus a void of air to let it breathe. We only did the internal detail at ground floor because it was only ground floor that the walls were a bit damp (with one wall in particular being very damp).

We also introduced French drains externally. 

 

This never makes any sense to me. Where is the wall "breathing to". If its a sealed void it can get out. If its not sealed, surely it rather renders EWI pointless?

[Roger440]

4 hours ago, Ben Weston said:

 

 

Yes, having looked into it a bit more, I think 200mm would be overkill. I think there's scope to go more than 100mm especially as there's relatively little cost difference in doing so. Perhaps 130mm or something like that? That, I think, would still allow fairly 'standard' decoration.

 

 

That's very kind, thank you. To be honest, I've spoken to quite a few RICS/RIBA-certified people now who all give me slightly different advice. I'm sure there's more than one right answer, of course! At this stage, I just want to understand as much as possible myself so that I have confidence in whatever route we eventually choose. 

 

 

Thanks. I think I'm satisfied that EPS will provide enough permeability for what we need so long as we render in lime internally and use a lime, or lime-like, render externally. Still not sure which external render to go for but we can come back to that. The main thing is establishing how much is being added to the walls so our architect can sort the roof on the working plans.

 

Thanks all for your very detailed help as always.

 

Are you really sure EPS has the required permiability. I doubt it very much.

 

Ask for the actual values. Compare to a pure lime product. I think you will be surprised.

 

Almost everyone claims "breathability". Pretty much everything is. But at what level. If they wont tell you, theres probably a reason for that.

 

I know im in danger of looking like an extremist limeist (is that a thing?) but i know what i see.

[SimonD]

14 hours ago, Roger440 said:

Do you have any thoughts on their interior systems?

 

I haven't looked at their current IWI systems so can't really comment on those.

[hb1982]

On 02/02/2022 at 14:40, Ben Weston said:

 

 

Yes, having looked into it a bit more, I think 200mm would be overkill. I think there's scope to go more than 100mm especially as there's relatively little cost difference in doing so. Perhaps 130mm or something like that? That, I think, would still allow fairly 'standard' decoration.

 

 

That's very kind, thank you. To be honest, I've spoken to quite a few RICS/RIBA-certified people now who all give me slightly different advice. I'm sure there's more than one right answer, of course! At this stage, I just want to understand as much as possible myself so that I have confidence in whatever route we eventually choose. 

 

 

Thanks. I think I'm satisfied that EPS will provide enough permeability for what we need so long as we render in lime internally and use a lime, or lime-like, render externally. Still not sure which external render to go for but we can come back to that. The main thing is establishing how much is being added to the walls so our architect can sort the roof on the working plans.

 

Thanks all for your very detailed help as always.

 

In my case, 1930 semi detach with original pebble dash, I applied 100mm EPS and K-Rend, normal plaster on internal faces. Loose pebble dash was brushed off and retained. EPS stick on retained pebble dash surface plus mechanical fixing. Bottom EPS layer supported by a track system. I did my own IES fabric analysis and I was satisfied there is no predicted condensation risk. All wall DPC was checked carefully and the suspended floor ventilation had been retained. Good breathable paint is used for all surfaces (including external wall below DPC)

 

The house is ventilated internal with mechanical extraction, trickle vent air make-up. I am not a fan of MVHR in general as I have seen too many MVHR failure in my working life. 

[Gus Potter]

On 28/01/2022 at 10:02, Ben Weston said:

Hi all,

 

We have an 1870s cottage built with 9 inch solid walls. We're adding an extension off the back which will be built to new cavity spec but we need to get the 3 walls of the original house up to standard.

 

There seems to be so much conflicting advice and 'old wives tales' when it comes to managing damp, solid walls and insulation. The current red brick solid walls are pebbledash rendered on the outside. There are no signs of rising or penetrating damp (though we are looking at an injected DPC as part of our renovation works) and, despite there being no damp issues, I believe the cementitious render won't help the breathability?

 

It's been suggested we use EWI for the outer three walls and marry up with the cavity of the newer extension. This would be complemented with foil-backed plasterboard internally. I'm concerned that applying EWI on top of what we currently have might introduce damp issues by locking that water in the solid wall with nowhere to go.

 

The original plan was to chip the pebbledash off, render in lime so it can breathe and insulate internally instead but I'm open to EWI if it's suitable in this situation.

 

Can anyone help advise?

Just wondering..

 

Sounds like your extension may have lots of glazing for example so you are needing to do some compensatory U value calculations.

 

Have you really looked at this in the round. It's an old house and to insulate the original walls is going to cost a lot and you'll loose gross internal floor area if you do something on the inside which could impact on the value of the house. It's also going to be pretty disruptive.

 

I would have a good review of your strategy before committing to messing with the original walls.

 

EWI sounds good.. but what about the rain water pipes, the apprearance of the eaves and roof overhang, the ingoes to the windows.. you could make your house look cheep and nasty from the outside?

 

Now is the time to take a step back, really test your design approach, make sure you are doing the right thing before you commit. It may be that you need to go back and review the extension design. Reviews can be good as you may actually end up with something better!

 

 

 

 

 

Edited February 4, 2022 by Gus Potter

[saveasteading]

On 02/02/2022 at 11:55, Adsibob said:

a RICS surveyor who has expertise in designing these kinds of systems.

Agreed. There are so many optional ways to get RICS (including auctioneers, estate managers, estate agent)  that you must ensure that building construction is their speciality.

[Adsibob]

2 hours ago, saveasteading said:

Agreed. There are so many optional ways to get RICS (including auctioneers, estate managers, estate agent)  that you must ensure that building construction is their speciality.

His speciality is actually diagnosing and solving damp problems in old houses and designing roof details. Our house is almost 100 years old and had quite a lot of damp, so before insulating it we needed to resolve that. So that is why we consulted him. He's also a nice guy and not stupid expensive.

[saveasteading]

That's good then.

I came across a really interesting paper on rising damp in stone buildings. It basically says that damp rises to about 1m, and to live with that and line the inside. Not always possible (or easy) though.

So we will be applying a bitumen liner 1m up from dpc .

[Ben Weston]

On 04/02/2022 at 00:21, Gus Potter said:

Now is the time to take a step back, really test your design approach, make sure you are doing the right thing before you commit. It may be that you need to go back and review the extension design. Reviews can be good as you may actually end up with something better!

 

Thanks! We're not currently living in the house. It's being stripped back to only the outer 3 walls - new roofs, new doors, new windows, new floors, etc. The disruption and challenges of marrying it up with the extension are moot. The extension design isn't really a concern to be honest: we're actually going to build that first, marry it up with the existing house and 'do' the original house last.

 

The plans are already signed-off (which took 4 months) so not too keen on revisiting anything there.

 

In other news, architect came back having done his research and suggested an injected DPC, leaving the cement render on and using an EPS insulation system on the outside. He'd spoken to the National Insulation Association and Weber, who he works with for most of his projects. That said, the suggestion seems all wrong to me.

 

I want to go back and suggest that the whole house (old and new) are covered in the same external insulation system to ensure continuity. I think it should be, in principle:

 

Breathable external render > 100mm - 130mm rockwool or woodfibre > solid brick wall (block wall in new extension) > breathable internal plaster & breathable paints.

 

No injected DPC. Both renders/plaster likely to be hydraulic lime or similar. This seems consistent with most of the advice I've got here and from specialists in older buildings.

 

Any thoughts? Should we be doing something different to the block walls? Am I way off the mark?

Edited February 5, 2022 by Ben Weston

[Adsibob]

49 minutes ago, Ben Weston said:

I want to go back and suggest that the whole house (old and new) are covered in the same external insulation system to ensure continuity.

I don’t think this will work. Take a look at the exterior of your old house. How will all of its architectural features, window reveals, soffits etc cope with 100mm build up of insulation externally. I wanted to do this but was strongly advised against it because you ruin the look of your old house.

[Ben Weston]

4 minutes ago, Adsibob said:

I don’t think this will work. Take a look at the exterior of your old house. How will all of its architectural features, window reveals, soffits etc cope with 100mm build up of insulation externally. I wanted to do this but was strongly advised against it because you ruin the look of your old house.

As I said, nothing is remaining. The windows, doors, roofs are all being replaced. The architect is designing it with whatever thickness we add on in mind: he's assuming around 100mm.

Edited February 5, 2022 by Ben Weston

[Roger440]

19 hours ago, saveasteading said:

That's good then.

I came across a really interesting paper on rising damp in stone buildings. It basically says that damp rises to about 1m, and to live with that and line the inside. Not always possible (or easy) though.

So we will be applying a bitumen liner 1m up from dpc .

 

That is EXACTLY the wrong thing to do. Where on earth did you read that?

 

Before you ruin your house, you would do well to aquaint yourself with these:

 

https://www.heritage-house.org/

https://www.periodproperty.co.uk/forum/viewforum.php?f=1

 

[Roger440]

2 hours ago, Ben Weston said:

 

Thanks! We're not currently living in the house. It's being stripped back to only the outer 3 walls - new roofs, new doors, new windows, new floors, etc. The disruption and challenges of marrying it up with the extension are moot. The extension design isn't really a concern to be honest: we're actually going to build that first, marry it up with the existing house and 'do' the original house last.

 

The plans are already signed-off (which took 4 months) so not too keen on revisiting anything there.

 

In other news, architect came back having done his research and suggested an injected DPC, leaving the cement render on and using an EPS insulation system on the outside. He'd spoken to the National Insulation Association and Weber, who he works with for most of his projects. That said, the suggestion seems all wrong to me.

 

I want to go back and suggest that the whole house (old and new) are covered in the same external insulation system to ensure continuity. I think it should be, in principle:

 

Breathable external render > 100mm - 130mm rockwool or woodfibre > solid brick wall (block wall in new extension) > breathable internal plaster & breathable paints.

 

No injected DPC. Both renders/plaster likely to be hydraulic lime or similar. This seems consistent with most of the advice I've got here and from specialists in older buildings.

 

Any thoughts? Should we be doing something different to the block walls? Am I way off the mark?

 

You really should aquait yourself with proper facts as per my message above.

 

As i posted elsewhere on the forum, ive spent the last 12 months sorting out mine and undoing the kind of stuff your are being advised to do. To be honest, i was sceptical. The results however, speak for themselves. 

[Ben Weston]

54 minutes ago, Roger440 said:

 

You really should aquait yourself with proper facts as per my message above.

 

As i posted elsewhere on the forum, ive spent the last 12 months sorting out mine and undoing the kind of stuff your are being advised to do. To be honest, i was sceptical. The results however, speak for themselves. 

 

Sorry, I'm not really sure what this passive-aggressive comment refers to. I'm here specifically to listen to all advice, yours included. However, "proper facts" do need supporting. Everyone considers their opinions to be "proper facts", with all due respect. What haven't I listened to?

Edited February 5, 2022 by Ben Weston

[Roger440]

55 minutes ago, Ben Weston said:

 

Sorry, I'm not really sure what this passive-aggressive comment refers to. I'm here specifically to listen to all advice, yours included. However, "proper facts" do need supporting. Everyone considers their opinions to be "proper facts", with all due respect. What haven't I listened to?

 

Im suggesting you have a read of the links i posted. I could write it all myself, but to be honest, my attempt would likely be half arsed.

 

Ive no idea why you think im "passive aggresive"????

 

Have a read of some useful info IS my advice.

 

Not sure why i bothered now...........................