Is thin insulation board an option for improving solid brick?

[d000hg]

Our 1870 house has solid brick walls which have about the same u-value as leaving the window open!

The two normal options are to build an internal stud wall with insulation inside the walls, or to insulate the external walls. The 2nd option we just don't like, certainly not right now - the former loses some room space but would be an option in some rooms.

However our main living room has original, ornate coving and pulling the walls in 6" would ruin that. We would rather keep it than reproduce it.
It looks like we could lose 1-2cm of wall and blend it in just fine so I wondered if there would be any benefit to getting thinner insulating sheet material of this thickness. I don't know what's out there but am thinking some kind of hard foam sheeting we could panel with then skim/paint/paper as normal.
Does such stuff exist and would it make any detectable difference? Maybe it's something worth doing when we redecorate as it wouldn't add much time... in fact if we removed the plaster we might then have a good inch to play with if we affixed such a product to the bare brickwork and could skim on top?

Is this something people ever do? Any products I could look into?

 

[opps]

I have seen 27mm foam insulated plasterboard that you could dot and dab. I have no idea about how much it would improve the µ values though. I guess that you would need to hack away some of the plaster to see how much you have to play with (or randomly drill holes until you hit brick and see how deep the holes are.

You may want to post your question in the plastering subforum

https://www.diynot.com/diy/forums/plastering-rendering/

There are lining papers that claim to have improved thermal qualities and paint additives that make similar claims. I have no direct experience of either class of products and would strongly suggest that you thoroughly research them.

https://www.gowallpaper.co.uk/erfurt-mav-wallrock-thermal-liner.html

https://www.rawlinspaints.com/home/...753-thermilate-thermalmix-paint-additive.html

 

[d000hg]

I wonder if there's a way to directly measure this stuff, try and calculate u-values in my existing house? You can get those infrared thermometers, it would be a diverting nerdy project

 

[d000hg]

I'd be dubious of paper or additives personally though. An inch of insulating material sounds more feasible but then the planning regulations stipulate minimum thickness and don't seem (?) to allow you to use thinner layers of higher-tech material which perhaps suggests otherwise.

You'd kind of imagine just glueing 1 inch of polystyrene packing foam on solid brick would make some noticeable difference thermally though not practically

 

[opps]

I guess that the manufacturers of the insulated plasterboard publish the µ values on their websites.

I don't know how much an infrared thermometer would help though. It will tell you the temperature of the existing plaster on your wall but it wont take into account the temperature outside and the "natural" ambient temperature inside excluding heat sources such as light from windows, heat from your fridge, etc. Oh and the heat generated by you being in the house in the first place to measure things- its all a bit "is the cat in the box dead, or alive or both simultaneously...

However it would be pretty informative if you did a before and after.

 

[opps]

I'd be dubious of paper or additives personally though. An inch of insulating material sounds more feasible but then the planning regulations stipulate minimum thickness and don't seem (?) to allow you to use thinner layers of higher-tech material which perhaps suggests otherwise.

You'd kind of imagine just glueing 1 inch of polystyrene packing foam on solid brick would make some noticeable difference thermally though not practically

Apropos building regs- don't those apply to new builds rather than trying to improve existing properties?

 

[d000hg]

Apropos building regs- don't those apply to new builds rather than trying to improve existing properties?

Absolutely I just mean those regs presumably exist for some reason - if you could get the same effects from thinner, more advanced materials wouldn't that be allowed? As I understand it, you just have to build new walls/roofs with insulation measured in thickness not effectiveness?

 

[opps]

I am out of my depth here, but I would imagine that the rockwool types of insulation are less efficient than polystyrene (per cm of depth). The former however are easier to work with without having to worry about leaving gaps, and possible better with regard to fire resistance.

Again, I confess to knowing very little about the subject...

 

[endecotp]

Insulation boards will always have a layer of plasterboard, or similar, over the top; that’s typically 12.5mm but maybe 9mm could be possible. That would leave you 11mm of insulation with your 20mm space budget. 11mm of celotex, or similar, will have a thermal conductivity of about 2 W/m2K. Your existing walls might have a U-value of 2.7 W/m2K, so adding another 2 W/m2K will bring it down to about 1.2, i.e. you will slightly more than halve the heat loss through the wall.

Another option might be a Marmox type board, which is extruded polystyrene between thin cement facings. They are normally tiled over, but they might take skim plaster (anyone know?). That would get a slightly better U-value than celotex + plasterboard.

You might be able to get more depth by first removing the existing plaster from the wall.

More exotic materials do exist. For example there are magnesium silicate boards that can do the job of the plasterboard with less thickness. And there are some fancy insulation products e.g. vacuum insulation panels - which have the significant disadvantage that if you ever bang in a nail to hang a picture, the vacuum is lost.

 

[oldbutnotdead]

Marmox is good stuff & yes you can skim it and cut socket boxes into it- but it has similar performance to other solid insulation (so 25mm will be a lot better than nothing but 70mm would be optimum). You can fix it with screws or dot and dab (there's technical data somewhere)

There is a slight issue with hacking the existing plaster off- technically if you do that you are required (under building regs) to insulate the wall to a modern standard (70mm solid/100-odd mm rockwool). If you don't hack the plaster off then you can do what you like (aka you aren't required to insulate, you can if you want to but nobody needs to know).

I can understand your desire to keep the coving- have you had a search online to see if it is a current style? If so then it might not be a dealbreaker to replicate it (by getting someone in who knows what they're doing I mean).

EDIT Be wary of companies flogging magic superthin super effective insulation- insulation is all physics and it isn't that easy, most of the miracle products I've looked at are long on claims of 'save up to 50% on your heating bills' and very short of actual measured thermal performance (R value or U value certified by BBA are usually trustworthy). Also be aware of payback times- cost per sq m aggregated over 20 years versus energy savings.

 

[option_brum]

I've been doing a lot of research into this, as we are in a Victorian end-terrace, so more external wall & potentially more space lost.

An Irish architect has published papers showing that for solid walls you don't want to go below a U-value of 0.5 with internal insulation. Considering that solid brick walls (9", 225mm) usually have a U-value of 2.0 or worse, a 75% improvement is massive.


My plan is to remove the existing plaster (some of which is in a bad condition anyway) & fix 25mm of PIR insulation directly to the walls, with 12.5mm of plasterboard over. I reckon the current plaster is 20-30mm thick. So, could lose 10-20mm depth from the walls, which is acceptable.

To meet the current Building Regs of walls being no worse than U=0.30, would need 75mm of PIR. Which would lose 60-70mm depth from the walls, which is unacceptable.
The thicker boards are also 66% more expensive.

 

[d000hg]

I've been doing a lot of research into this, as we are in a Victorian end-terrace, so more external wall & potentially more space lost.

An Irish architect has published papers showing that for solid walls you don't want to go below a U-value of 0.5 with internal insulation. Considering that solid brick walls (9", 225mm) usually have a U-value of 2.0 or worse, a 75% improvement is massive.

Can you recall why? Maybe you have the paper? I have heard that these houses are designed to "breath" so blocking up all draughts can exacerbate damp issues, maybe it is related?

My plan is to remove the existing plaster (some of which is in a bad condition anyway) & fix 25mm of PIR insulation directly to the walls, with 12.5mm of plasterboard over. I reckon the current plaster is 20-30mm thick. So, could lose 10-20mm depth from the walls, which is acceptable.

To meet the current Building Regs of walls being no worse than U=0.30, would need 75mm of PIR. Which would lose 60-70mm depth from the walls, which is unacceptable.
The thicker boards are also 66% more expensive.

Sorry, what is PIR? And is that the case that the BR do talk about thermal efficiency rather than just giving blanket figures for minimum depth? That's useful to know.

 

[d000hg]

Insulation boards will always have a layer of plasterboard, or similar, over the top
...
Another option might be a Marmox type board, which is extruded polystyrene between thin cement facings. They are normally tiled over, but they might take skim plaster (anyone know?). That would get a slightly better U-value than celotex + plasterboard.

You might be able to get more depth by first removing the existing plaster from the wall.

More exotic materials do exist. For example there are magnesium silicate boards that can do the job of the plasterboard with less thickness. And there are some fancy insulation products e.g. vacuum insulation panels - which have the significant disadvantage that if you ever bang in a nail to hang a picture, the vacuum is lost.

I mean you could 'tile' your wall with slimline double glazing panels and cover this over - similarly impractical but interesting such products exist.

I hadn't realised these boards all require plasterboard, something that could take a skim sounds preferable.

Marmox is good stuff & yes you can skim it and cut socket boxes into it- but it has similar performance to other solid insulation (so 25mm will be a lot better than nothing but 70mm would be optimum). You can fix it with screws or dot and dab (there's technical data somewhere)

There is a slight issue with hacking the existing plaster off- technically if you do that you are required (under building regs) to insulate the wall to a modern standard (70mm solid/100-odd mm rockwool). If you don't hack the plaster off then you can do what you like (aka you aren't required to insulate, you can if you want to but nobody needs to know).

I can understand your desire to keep the coving- have you had a search online to see if it is a current style? If so then it might not be a dealbreaker to replicate it (by getting someone in who knows what they're doing I mean).

Interesting point on the regs, do you now where I can find that clause because I'd no idea. I mean, in practice it's probably a non-issue and if you hadn't told me I'd have proceeded blissfully unaware But it's good to know these things.

I don't know if I could get a modern reproduction of the coving, my guess would be yes but then removing the original stuff sounds a bigger job and I end up redecorating the entire room and potentially replacing the ceiling too?
However I kind of just don't WANT a modern version. Original features are nice to keep where possible and this isn't always the most practical option!

 

[option_brum]

It's the 'Breaking the Mould' papers from Joseph Little;
http://www.josephlittlearchitects.com/articles


PIR;
Polyisocyanurate (PIR) is one of the most efficient insulation material used in construction.
It's the Kingspan/Celotex insualtion boards that are available either stand-alone or attached to plasterboard.

 

[d000hg]

When we had a socket fitted, we found we have ~1/2" thick plaster at least on the internal brick walls... not quite enough for a slimline box! We have some rising damp issues which mean at least some of the plaster is going to have to be removed on the exterior wall. So it could be worth stripping it all, although even the 10-12mm board would seemingly do some good - notably reducing condensation - so there's the possibility we might even be able to board on top of the existing wall with marmox whenever we come to redecorate.