The next most effective thing to do is External wall insulation. However that'll mean that you'll loose the whinstone look. (unless you pay a _lot_ to get whinstone like shims put on after)

The alternative is to have internal wall insulation: https://www.insulationsuperstore.co.uk/product/vacutherm-vac...

This is as effective as ~150mm of rockwool, but only 20mm thick. So this can be stuck behind plaster/plasterboard.

but its not easy to work with, or widespread yet.

Yes, it's one of the top recommendations (internal wall insulation) on my EPC and have had a survey. 60mm PIR boards would be used. Turns out I wouldn't have to sacrifice much space but would have to pay a bit extra replacing the cornices.

There are some regional grants in the UK that can cover a large portion of the amount. For me, it is £7.5K, with the quote I received at £9K. This would not have covered the kitchen or bathroom.

Going by EPC recommendations and numbers alone, I can reduce my energy requirement by about 40%.

Be super careful internally insulating an old house. This can cause _a lot_ of humidity problems if not done _exactly_ right. Very often, there is no way to do it exactly right!

I would recommend you to consider breathable internal insulation materials, combined with breathable finish layers of course! Some hints.

Roof (or attic floor) insulation is the most important. I imagine those have been done properly already.

Walls. There's industrial products for walls, like Xella Multipor. You may also want to have a look at eco products, especially if working on the place yourself. Hempcrete is a fairly forgiving material that works rather well for this purpose. Rather expensive to have it installed, but easy to do yourself.

Ground floors. Have a look at foam glass [0] insulation. It both stabilises and insulates, is moisture and fire proof, not horribly expensive and saves you from having to put in a layer of concrete. Not super well known yet, but growing in popularity. A wonderful material and super easy and forgiving to work with. A no-brainer really in many cases...

[0] https://en.wikipedia.org/wiki/Foam_glass

The one key rule that you should always follow is to have your water-impermeable layer on the warm side of the insulation.

So, I'd recommend against breathable internal insulation, because that will make your solid wall (water-impermeable layer) colder, but still exposed to the humid inside air, and this could cause condensation on that cold wall. As an example of this, I have rubbish double glazing, and when the temperature drops outside, if I have just the curtains drawn (which don't really provide any insulation) then I'm fine, but if I lower the thermal blackout blinds, then I get loads of condensation on the inside of the windows, which I remove with a window vac in the morning.

Breathable external insulation is less of a problem, because it warms up the wall, while exposing it to the comparatively dry air from outside, so you shouldn't get any condensation.

> The one key rule that you should always follow is to have your water-impermeable layer on the warm side of the insulation.

This very much holds true in 99% of modern homes.. except if you build your entire wall breathable. That is how we did our walls. From inside to out:

- breathable paint. Lots of conventional options available. We made a really nice casein paint with low fat cottage cheese and lime paint as the main ingredients :-)

- lime plaster. 1/3 slaked lime powder, 2/3 sand.

- 1.2m of straw

- lime plaster

Agreed, houses with insulation have a vapour barrier behind the plasterboard for this reason: counterintuitively, the warm internal air carries a lot more moisture than the cold air outside. The partial pressure of water vapour is higher inside the house than outside, so the dew point of the internal air is higher than the outside temperature (dew point depends on water content).

If there's a way for that moisture to diffuse through the wall from inside, through the insulation, to the cold structure (which would be colder than before due to the internal insulation), the conditions are right for condensation to form. Those conditions are: surface temperature ≤ dew point.

Condensation can be prevented by a combination of:

1. Reduce the rate of moisture diffusion from the interior (seal the rooms and use a vapour barrier)

2. Lower the dew point of the air in the "cold" structural areas by ventilating the cold space to outside, so the moisture can exit (this is why houses have air bricks, vents in the roof, etc.)

3. Prevent the building structure from being colder than the internal dew point (i.e. use external insulation)

Had to sign up for this. Take extra care to use appropriate materials for a house this age or you'll create more problems than you solve. Solid stone walls need to breathe!

Make sure you've spoken with a surveyor specialising in heritage property too.

PIR boards are almost certainly unsuitable.

https://www.victorian-house.co.uk/ (be sure to pick up a copy of the Haynes Victorian House manual, it's a gem)

https://www.lime.org.uk/community/boards-insulation.html

I'm currently having to undo poor choices of modernisation on a building of the same age, which caused tremendous problems with damp.

Another good resource is https://www.neighbourhoodconstruction.org e.g their page on Thermal Envelope > Bio aggregate https://www.neighbourhoodconstruction.org/bio-aggregate/

Thanks for taking the time to sign up.

I intend to use rockwool for the floor and roof crawl space.

Luckily I have a relative in the field who can share advice. I am conscientious of the condensation issue. There's a company local to me who use hemp boards which are porous. What you say is definitely something to consider given the extent of work involved, and to possibly undo.

I followed your link, but am confused and/or doubtful:

how do you replace 150mm of rockwool with 20mm of anything other than a good vacuum? It says that they are 'very low internal pressure' - but if it contains any kind of gas (which i presume it must do - air if nothing else) then the conductivity does not depend on pressure until the mean-free-path has increased to be > the width of the container.

Is this product real? What is it about the physics that I am not understanding?

And how do you maintain the 'very low internal pressure' over the decades that you will need it for?

Thanks.

From what I've seen, its basically a honeycomb with a thick plastic coated foil to act as an atmospheric barrier. I came across it from a number of sites, but I've not managed to get any samples yet.

> And how do you maintain the 'very low internal pressure' over the decades that you will need it for?

now thats a million dollar question. I don't know.

https://en.wikipedia.org/wiki/Vacuum_insulated_panel Looks like the thing. So, yeah, very good vacuum. It's apparently decades for the lifespan, but much of it boils down to the materials being used.

> conductivity does not depend on pressure

I think it might be fumed silica aerogel at about 0.1 bar.

This paper describes the use of the same material for building insulation:

https://www.researchgate.net/figure/a-The-thermal-conductivi...

I suspect the key issue will be maintaining that low pressure for the ~100 year lifespan of the building. Perhaps future versions will come with micro pumps so that once per year the pressure can be pumped back down to 0.1 bar. Looks like for about a dollar you can buy a little 3 volt vacuum pump. One per panel out to do a decent job.

It is a good vacuum. They work but are expensive and a single nail destroys the whole panel, but maybe cheaper than the loss of floor space.

An easier solution is plasterboard already bonded to PIR or XPS. The XPS is cheaper and I don't think it will make a massive difference depending on all the other challenges like windows and doors. You can simply stick this to existing walls with adhesive foam and then dry-line or skim the boards afterwards.

To do it well, though, you will often need to cut out/remove any laminate flooring so the boards can meet the floor and they won't do anything about leakage between floors, which can be significant.

> plasterboard already bonded to PIR

As you point out they are normally ~25mm or so of EPS/XPS. which doesn't do _much_, especially compared to 600mm of stone. Plus XPS is pretty flammable, so with electricity cables sandwiched between it, its not a great thing to have inside the house.

I work on energy systems modelling and how domestic thermal performance interfaces with that - the UK has not just "one of the oldest in Europe" it actually has the oldest in the world. Many European countries had a lot more post WWII construction so at least have cavity walls (even if in many cases not filled until later).

My understanding was that cavities should actually not be filled, since they allow water to drain out. Is that incorrect?

The issue is will the cavity system allow water to penetrate to the inner leaf which is bad and will cause internal dampness.

Cavities can be carefully partially filled with some type of insulation which allows the water soaking through the brick to evaporate and drain back out.

The standard technique is to use blown in EPS beads which allow for drainage downwards, reducing the chance that any water loading will make it through the insulation layer and to the inner leaf of the wall.

Problems with cavity insulation are often caused by:

-Treating walls which have a large amount of debris in the cavity, leading to water bridging

-Over-filling cavities which also leads to water bridging

-Treating walls with very large amounts of rain exposure, especially to driving rain for extended periods of time since this will lead to saturation of the cavity insulation system which may be unable to dry for months at a time. These walls should be externally insulated and clad instead.

In the UK context for example, houses in Wales and parts of the English South coast, the whole Southwest, the East of Scotland, and most of NI are in zones 3 and 4 in terms of wind driven rain exposure.

In zone 3 and 4, installers are required to carry out an assessment of site conditions and of cavity thickness as well as exterior wall finish. Older houses might have 50mm cavities, new properties often have 100mm or 150mm cavities. Obviously that reduces the changes of water soaking through.

Approved Document C allows a full fill of insulation for a 75mm cavity on a fully rendered wall and on a 50mm cavity if clad with rain impervious material but requires 150mm for bare masonry.

Thanks for the detail! I have a 1930s house with, I think, unfilled cavities. I’ve always been put off looking into insulating because it seemed potentially harmful.