Can I insulate an 1880s stone house with insulation panels?

[Gary1111]

Is it possible fit insulation panels fitted to a metal frame to the walls inside the house?

Hopefully that would not cause damp, as there would be a gap between the wall and the non breathable insulation panel?

 

[Kearn]

No. It will cause damp.

You need breathable insulation and no air gap, one solid mass, but not too deep. Best bet is an insulated plaster straight onto the stones, which can follow the shape.

Stone walls however, can often be deep enough that the additional insulation doesn’t add much incrementally to the stones themselves. As long as the stone is dry and can breath. It’s a good insulator when dry, when wet it’s a great conductor. So, high ground levels, rainwater leaks, cement pointing/render/plastic paint… all this stuff will make the wall wet and sap heat from inside to out.

Assuming you have any of that externally/internally, once you remove it takes significant time for the mass to fully dry out. Rule of thumb about a month per inch of thickness.

 

[Lacan07]

Is it possible fit insulation panels fitted to a metal frame to the walls inside the house?

Hopefully that would not cause damp, as there would be a gap between the wall and the non breathable insulation panel?

How thick are these stone walls? As Kearn has indicated with really thick walls it gets to a point where insulation is irrelevant.

If you have a nice thickness of wall some insulating plaster will be the cherry on the cake, or if your walls are relatively flat you could think about wood fibre board.

If you batten a wall and apply PIR board you've created an airless gap where mushrooms can grow. The silver foil on the PIR board needs to be fully intact as you don't want the warm moist internal air to escape into the cold side of the insulation.

 

[aockenden]

Is it possible fit insulation panels fitted to a metal frame to the walls inside the house?

Hopefully that would not cause damp, as there would be a gap between the wall and the non breathable insulation panel?

Yeah there is definitely still a risk of damp / mould accumulation behind the panels. As Kearn said, one good option is an insulated breathable clay or lime plaster (which includes insulating aggregates instead of some or all of the sand) applied thickly directly onto the cold condensation-prone walls. These can improve things noticeably. We’re using this approach all over our old stone cottage.

If you wanted to stick with the insulation boarding approach on studs off the wall, you need to somehow get a really solid amount of ventilation behind the insulation boards and leave a good air gap of bare minimum 1 inch. You’d also be best advised to replace the standard foil-backed insulation boards between the studs with vapour-open / permeable / breathable insulation materials like wood-fiber boards or even sheepswool if it can be held in place vertically properly. And then you’d want to be sure you’re plastering over it with a good breathable lime or clay plaster and finishing with breathable mineral-based paints lime limewash or clay paint. The ventilation and the breathable insulation material + finishes will probably make that approach fairly safe.

 

[Lithgae]

I'm not sure I agree with this risk of damp. If you use impermeable insulation internally and ensure all joints are sealed, then damp can't get into the wall from inside. With the very thick walls in older houses its unlikely that rain will penetrate very far in so the main thing is to ensure that there are no leaks from the roof or walls etc.

I used to worry a lot about breathability in my old house, but I have come around to the idea that its breathability on the external surface that's most important and dealing with ground moisture in houses where there is no DPM.

If you choose to go that way, modern PIR insulation can be stuck directly to the walls and plasterboard directly over it. I think you do have to consider how much benefit you would get and whether its right to rip down lath and plaster that is in good order, but even lath and plaster was a 'modern' method at one point and replaced plaster on the hard so times change.

 

[thebadger7]

The other consideration with insulating solid walls in this way is you lose the benefit of thermal mass. The walls now sit outside the thermal envelope of your property, so you won't benefit from smoothing out of temperatures, which is becoming more important in summer (thermal mass of solid walls keeping houses cooler). I'd personally use a small layer of insulating render with no air gap, but if it's a thick wall then should be a good insulator already if dry.

 

[jamest]

I wouldn't go near PIR because if it is exposed to flame, even if it doesn't actually burn, it releases toxic fumes (hydrogen cyanide and carbon monoxide) that will kill you quickly. I remember good ol' Pete Ward doing a test of some allegedly non-flammable PIR insulation that burnt like nobody's business - don't believe what the companies tell you - remember Grenfell. Always use sustainable insulation that does not release so much toxic gas - cork is probably best for that.

 

[Lithgae]

The other consideration with insulating solid walls in this way is you lose the benefit of thermal mass. The walls now sit outside the thermal envelope of your property, so you won't benefit from smoothing out of temperatures, which is becoming more important in summer (thermal mass of solid walls keeping houses cooler). I'd personally use a small layer of insulating render with no air gap, but if it's a thick wall then should be a good insulator already if dry.

I would question the benefit of thermal mass, certainly in the climate I live in. The north facing room that I am currently insulating never gets too warm, even on the warmest days. This might be different for south facing rooms in the south of England, so its horses for courses.

Another problem with thermal mass is how you use a room, and how you heat the house. If you are in the room all day every day, then you might benefit from thermal mass, but if you want to be able to get a room to heat up quickly so you can use it on demand, then internal insulation will probably win out.

 

[CliffordPope]

I would question the benefit of thermal mass, certainly in the climate I live in. The north facing room that I am currently insulating never gets too warm, even on the warmest days. This might be different for south facing rooms in the south of England, so its horses for courses.

Another problem with thermal mass is how you use a room, and how you heat the house. If you are in the room all day every day, then you might benefit from thermal mass, but if you want to be able to get a room to heat up quickly so you can use it on demand, then internal insulation will probably win out.

An example would be if you lived in a Norman castle with 10 foot thick walls.
The walls would be at virtually the same temperature all the year round, which for 6 months of the year would be colder than the air inside. So any activities related to human activities, such as breathing, cooking etc, would produce moisture which would condense on the inside of the walls. Insulation to separate the thermal mass might then be a good idea.

That's perhaps an extreme case, but clearly there must come a wall thickness where this factor becomes significant.
As an example I did construct a (small) stone clock tower about 30 years ago at one end of our house, a folly perhaps you could call it, with solid stone walls. In summer it runs with condensation and produces puddles on the floor. It doesn't matter in this case because it's only a stone floored scullery and washhouse below, so is pretty damp anyway.

 

[Lithgae]

I wouldn't go near PIR because if it is exposed to flame, even if it doesn't actually burn, it releases toxic fumes (hydrogen cyanide and carbon monoxide) that will kill you quickly. I remember good ol' Pete Ward doing a test of some allegedly non-flammable PIR insulation that burnt like nobody's business - don't believe what the companies tell you - remember Grenfell. Always use sustainable insulation that does not release so much toxic gas - cork is probably best for that.

Grenfell is a slightly different scenario to most internal house insulation projects. In a two story house, by the time a fire has got to the point that it has burned through the (non flammable) plaster and started to burn the insulation, you would expect fire alarms to have sounded and residents to be out of the building. External insulation on high rise flats are a different animal.

I suppose its about tradeoffs. Cork is nice but about half has effective as PIR

 

[Lithgae]

An example would be if you lived in a Norman castle with 10 foot thick walls.
The walls would be at virtually the same temperature all the year round, which for 6 months of the year would be colder than the air inside. So any activities related to human activities, such as breathing, cooking etc, would produce moisture which would condense on the inside of the walls. Insulation to separate the thermal mass might then be a good idea.

That's perhaps an extreme case, but clearly there must come a wall thickness where this factor becomes significant.
As an example I did construct a (small) stone clock tower about 30 years ago at one end of our house, a folly perhaps you could call it, with solid stone walls. In summer it runs with condensation and produces puddles on the floor. It doesn't matter in this case because it's only a stone floored scullery and washhouse below, so is pretty damp anyway.

Totally agree. I remember years ago when I was first starting to think and plan about insulation etc in old houses and I would always hear this mantra that thermal mass is desirable, ergo internal insulation is bad. The more I started to understand it I could see that thermal mass is great if you live in the desert and get extremes of temperature day and night. In that scenario a 2 foot thick wall soaks up that heat during the day and evens out the internal temperatures over a 24 period. Where I live most of the year I am just heating up a big block of stone that is always conducting from inside to out.

Another factor is that most old houses will already have a significant amount of thermal mass on the internal walls. When I think of the room I am currently working on, there are two brick/stone walls internal wall rendered on the hard and two external walls which I will be insulating. The two internal walls will give me all the thermal mass I could possibly want.

I also find it interesting to see the opinion on the thread that a dry stone wall is a good insulator. Depending on construction and who you believe it could have a u value as poor as 3, or at very best 1ish, while even a wall consisting of nothing but 50mm of PIR would get about 0.4.

 

[Kearn]

I'm not sure I agree with this risk of damp. If you use impermeable insulation internally and ensure all joints are sealed, then damp can't get into the wall from inside. With the very thick walls in older houses its unlikely that rain will penetrate very far in so the main thing is to ensure that there are no leaks from the roof or walls etc.

That logic works, if your house is floating.

However, the ground moisture will happily track up and evaporate into the void. With an air gap, the dew point has likely moved to that inside face of the wall. So that trapped moisture will condensate on that surface…

People like to debunk rising damp, and in many circumstances it’s the scape goat for other water sources.

However, the image below shows the damage done by ground moisture travelling up our stone plinth wall.
Plinth was enveloped in and out by inch + thick excessively hard cement.
That curved section on the under side of the sole plate, is rotten heartwood. Which had been sat soggy for decades. For the 500 years before that, it had happily been doing its job.

Now, our barn was built directly onto the limestone bedrock, which doesn’t do a great job of shifting rainwater through it, so the ground may be wetter than some geologies, but the point stands. The entire central rubble section of that wall was of the perfect consistency for making sand castles when initially exposed.

 

[Lithgae]

That logic works, if your house is floating.

However, the ground moisture will happily track up and evaporate into the void. With an air gap, the dew point has likely moved to that inside face of the wall. So that trapped moisture will condensate on that surface…

People like to debunk rising damp, and in many circumstances it’s the scape goat for other water sources.

However, the image below shows the damage done by ground moisture travelling up our stone plinth wall.
Plinth was enveloped in and out by inch + thick excessively hard cement.
That curved section on the under side of the sole plate, is rotten heartwood. Which had been sat soggy for decades. For the 500 years before that, it had happily been doing its job.

Now, our barn was built directly onto the limestone bedrock, which doesn’t do a great job of shifting rainwater through it, so the ground may be wetter than some geologies, but the point stands. The entire central rubble section of that wall was of the perfect consistency for making sand castles when initially exposed.

Every structure is different. I think it is about understanding the one you are dealing with and the risks involved. If the house has a DPC then you can have good confidence that damp will not rise past that point. If it has no DPC but a vented, suspended floor then any dampness rising could vent through that route. If there is no DPC and a traditional solid floor on earth then yes I would be cautious about impermeable internal insulation.

 

[Kearn]

Every structure is different. I think it is about understanding the one you are dealing with and the risks involved. If the house has a DPC then you can have good confidence that damp will not rise past that point. If it has no DPC but a vented, suspended floor then any dampness rising could vent through that route. If there is no DPC and a traditional solid floor on earth then yes I would be cautious about impermeable internal insulation.

Well, of course. Although most houses in certain groupings largely follow a similar model.

Either way, the original question was regarding an 1880s stone built building, which could possibly have had an early slate DPC. But, highly unlikely… hence the responses appropriate for that building being of traditional construction, and the risks of the proposed approach.

 

[Lithgae]

Well, of course. Although most houses in certain groupings largely follow a similar model.

Either way, the original question was regarding an 1880s stone built building, which could possibly have had an early slate DPC. But, highly unlikely… hence the responses appropriate for that building being of traditional construction, and the risks of the proposed approach.

I don't completely agree with that. My house was built in about 1820, then had substantial renovations in the 1880's part including a bay section added. The section that was added in the 1880's has a slate DPC. Parts of the house have solid floors and other parts have suspended floors. The risk of moisture travelling up the walls is far greater in the sections where the floor is solid. On top of that there were vastly different methods and materials in use in different parts of the country and in my own stone walls there are sections made from whinstone, sandstone and brick. Each of these materials is completely different with respect to porosity. On top of that there are environmental variations depending on where you are, water table, wind driven rain etc.

No matter what type of insulation is fitted there will be a risk, also no insulation carries the risk... of being very cold from trying to heat up 2ft stone walls

 

[CliffordPope]

risk... of being very cold from trying to heat up 2ft stone walls

Then why try and heat them? A traditional house would be heated by open fires giving out intense radiant heat. They heat things nearest to the fire -the occupants, the furniture, carpets, etc, and also the fireplace and chimney (and the cat curled up on the rug just in front of the fire). These re-radiate absorbed heat and also spread a certain amount of heat by convection of adjacent air. Why bother trying to heat up a large lump of stone wall across the room?

A modern equivalent is the overhead radiant heater fitted in shops and warehouses etc. You feel a beam of heat when you walk underneath them.

 

[GillesF]

This has always wondered me: I read that you should heat your house to x °C to avoid condensation. But how did people manage 100 years ago? Rooms were heated by fireplaces and there must have been times that no one was present to manage the fireplaces so the house was unheated.

Or does this advice apply mainly to modern houses (built with gypsum, cement, ...)?

 

[thebadger7]

I would question the benefit of thermal mass, certainly in the climate I live in. The north facing room that I am currently insulating never gets too warm, even on the warmest days. This might be different for south facing rooms in the south of England, so its horses for courses.

Another problem with thermal mass is how you use a room, and how you heat the house. If you are in the room all day every day, then you might benefit from thermal mass, but if you want to be able to get a room to heat up quickly so you can use it on demand, then internal insulation will probably win out.

That's fair enough. I personally can't stand overheating in summer, so tend to stay away from PIR. For example will be insulating our pitched roof with woodfibre sarking boards which should be more effective at reducing summer heat gains. For our brick walls I plan to use an insulating lime plaster as a compromise to improve U value a bit, but still allow some heat transfer so masonry (soft brick) doesn't become too cold in winter.

 

[Lithgae]

Then why try and heat them? A traditional house would be heated by open fires giving out intense radiant heat. They heat things nearest to the fire -the occupants, the furniture, carpets, etc, and also the fireplace and chimney (and the cat curled up on the rug just in front of the fire). These re-radiate absorbed heat and also spread a certain amount of heat by convection of adjacent air. Why bother trying to heat up a large lump of stone wall across the room?

A modern equivalent is the overhead radiant heater fitted in shops and warehouses etc. You feel a beam of heat when you walk underneath them.

Because we have Victorian houses we should live like Victorians? Be freezing cold in the winter except when 2 foot away from the fire. They also tended to wear heavy house coats indoors, have wingback chairs to contain the radiant heat. The reality is that is not the way people live these days.

They also used massive amounts of polluting coal to heat their houses.

 

[Lithgae]

This has always wondered me: I read that you should heat your house to x °C to avoid condensation. But how did people manage 100 years ago? Rooms were heated by fireplaces and there must have been times that no one was present to manage the fireplaces so the house was unheated.

Or does this advice apply mainly to modern houses (built with gypsum, cement, ...)?

Old houses would have been much more draughty. Fireplaces suck also air in through the all the gaps and expel air out of the chimney so there would have been much high rate of air exchange back then. I would imagine that would help keep the humidity down, compared to modern air tight houses.