If you are like us then you have been searching the internet far and wide looking for answers on how to insulate your stone or brick house to make it cosier.
With a lot of talks online about breathability and eco-friendly insulation, we found no definitive answer to the question of what should we insulate our stone house with and what types of insulation we should use.
We thought we would share the process we took and how we managed to decide our insulation type.
We insulated our solid walls to create a lovely warm and well-insulated home.
In this post I will explain the reasoning behind exactly why we chose this material to insulate our home and run through all the other alternatives that we came across.
Before we dive into what we used I might detail first as to why you would insulate your stone walls and how they need to be insulated differently to other walls such as cavity block walls.
If you already know then skip this part but if you didn’t know then this will hopefully explain a bit better.
Why insulate your stone walls
For me insulating our home well and properly was a must.
I am what we call around here a ‘cosy hole’ meaning I do like to be nice and warm in my home.
The climate in Ireland, especially the west where we live can be quite harsh and cost so insulating your house can make a massive improvement.
Stone or brick walls were originally constructed with the intention of keeping heat in the house and taking time to escape. The thicker the wall the longer it will take for the heat to escape.
So therefore a thick solid stone wall is already a good insulator, however with the way houses are now and the need for a higher Energy Rating in homes people are now looking to insulate their stone walls.
Heat leaving your home is broken down into percentages.
- The roof lets out about 25% of heat
- Windows and doors let out another 25%
- Walls let out about 35%
- And Floors let out a further 15% of heat.
So as you can see at the top of the list are the walls in your house with a whopping 25% of heat being lost through them.
This of course is what happens when a home is not insulated properly with the proper materials.
Why solid stone walls need to be insulated differently to cavity
So solid walls that are built using Stone or Brick are different to cavity block walls because they need to breathe.
The term ‘breathable’ or ‘breathability’ is often applied to many products which are only slightly vapoured permeable. In general, no synthetic modern materials should be applied to the masonry or plaster surfaces of historic buildings.
So in other words you should not slab straight onto your stone wall with a standard insulation board..
As shown in this diagram if you do insulate with your regular insulated slabs you will create moisture or condensation that is trapped in between your wall and insulation.
This of course means that you will cause great problems and could seriously damage the wall.
This is where the hot air from inside meets the cold from out behind the insulation and starts to sweat. It won’t be long then until you see the signs coming through your lovely newly plastered wall.
Types of insulation
So we have established so far that you cannot insulate your house with regular, synthetically manufactured insulation.
So what do we do with a stone wall? Well the answer is simple. We still insulate it.
But insulate it with breathable materials.
Materials such as Sheep’s wool, Wood boards and Hemp for example.
Here is a list of materials or methods that we looked at to insulate the walls in our home.
- External insulation (wrap)
- Sheep’s wool
- Hemp block
- Hemp pack
- Hemp wool
- Insulated plaster
- Thermal board (wood fibre)
- Gutex (wood fibre)
- Calistherm board
- Thermafleece CosyWool
- Stud wall and dry line
While we did look at insulating externally we felt it was best for us to insulate the internal boundary walls.
The material we chose for a number of reasons was hemp wool insulation. I will give reasons why we chose this type of insulation later.
What we had to consider before buying insulation
While we were choosing our final insulation there were several factors we had to think about that were specific to us.
So make sure that you do take this into consideration before you purchase.
- We wanted to insulate the house with something that required little skills or knowledge on how to install. Something that we could install ourselves and not have to pay someone to come in and install for us.
- We needed something like a stud wall to hang our ceiling from. Our ceilings were almost 11 foot high in the old house so I wanted to drop down to 8 feet and hang new joists. We thought it would make sense to sit the joists on top of a stud wall and kill 2 birds with the 1 stone. Just seemed logical.
- We are trying to avoid plastering with lime plaster on the inside if possible. I know that is almost impossible to do but it does mean finding a plasterer that uses Lime and also down the road looking for breathable paints etc. We know we will have to do this outside but are trying to minimise the cost inside as much as possible
So with these factors in mind we started to look at insulating our walls.
One by One I went through every possible insulation that I could find for an old solid wall stone house to try and determine which suited us best.
Lets start here with External Insulation.
1: External Insulation
The first one we will look at is an external insulation or what is known as a ‘wrap‘.
This requires you to slab external insulation onto the outside of the house.
There are so many types of materials that a wrap can use but the particular one we looked at was a tongue and groove wood board.
It is by quite a bit the more expensive and most people do not like it as it masks the stone or brickwork on the outside of the house that some people may want to leave exposed.
You also need a bit of an overhang as this will protrude from the wall quite a bit.
In this case our walls were already extremely thick and we felt that adding another 60mm plus onto the walls would not look right, especially around the windows.
The main reason we chose not to install this was price.
Even though you can receive a grant of up to €6,000 here in Ireland the price as you can see below was over our budget by quite a bit.
If you have the money and don’t want to keep any outside stone then go for this.
Installing it is straightforward enough, however, if you are not that familiar with using a trowel you are best off to get someone to install it for you.
Pros
- Great thermal performance
- Quick to apply
- Doesn’t take up inside space
Cons
- Expensive
- Bit difficult to apply compared to other insulations
- Doesn’t suite every house
2: Sheeps Wool
Sheeps wool is extremely easy to apply.
You can handle it without any gloves or masks.
It has surprisingly good thermal conductivity and works well as attic or ceiling insulation.
It is easy to apply between a timber stud or aluminium stud wall.
The reason why we did not choose this insulation to insulate our home was simply for the fact that it was a bit too flimsy.
All the demonstrations showed the wool being, for want of a better word, floppy and being tacked onto a wooden background while being installed.
We of course have a stone wall and thought that we would have to install it by tacking it onto the stud wall which surrounds it.
Also I figure that overtime it might droop and fall to the bottom of our stud wall.
Although we are not using this method to insulate our walls we will use it to insulate the ceilings.
Installation method
Pros
- Great thermal Performance
- Cheap
- Natural
- Easy to Install
- Quick to Install
Cons
- Lightweight
- Takes up internal space
3: Hemp Block
The Hemp block is extremely versatile. Mostly used for constructing walls it can also be used to insulate.
It can be used as internal or external insulation.
For this we focused on the 60mm internal block for internal insulation.
It is a thin block that would be stuck using adhesive on the boundary walls.
Reason we didn’t use this was for a few reasons.
1st was price. It seemed a bit more pricey then some other insulations.
2 the process required some good plastering skills, which would have to be outsourced of course.
Pros
- Solid
- Can be used internally and externally
- Good insulator
Cons
- Can be difficult to install
- Needs good plasterer finish
- Slightly Pricey
- Lower thermal conductivity than others
4: Hemp Pack
I must say I was very close to order this. It seemed to be a great fit to what we were trying to do at our home.
The idea is you would build your stud wall, pack it with the hemp mixture and it creates a solid wall against your original stone wall.
As you can see in this video here it is quite easy to do and quite a good solution.
It does save a lot of hassle introducing other materials such as adhesive, membranes etc.
Pros
- Easy to install
- Quick to install
- Doesn’t require too much
Cons
- Lower thermal conductivity than others
- Needs good plasterer finish
- Slightly Pricey
- Takes up internal space
5: Hemp Wool
This is what we actually chose to use for a finish.
Thermo Hemp is a natural hemp based wool product.
It is very similar to Sheeps Wool insulation but it is more sturdy and solid and this is why I chose it over Sheeps wool.
It comes in sheets that you can roll in between your timber stud frame.
It is easy to use and install and has a decent thermal conductivity with a Value of 0.040 W/mK.
The material is not extremely expensive either and we can install it ourselves which is a big plus.
I also contacted the manufacturer asking what kind of plasterboard can be attached to your timber stud and he told me any kind of plasterboard as long as it’s not foil back.
Pros
- Little equipment needed to install
- Good thermal conductivity
- Easy to install
Cons
- A bit Expensive
6: Insulated plaster
The process was appealing to me at first. I liked the idea of just having to layer on this plaster and the more you put on the warmer your home would be.
The more I thought about it the more I didn’t like the idea of it.
I’m not saying it’s wrong as a lot of people use it and have seen great results it’s just not for us.
I didn’t like the idea of getting a plaster to come in over and over again to plaster the same walls.
Also it was more expensive than I thought.
Pros
- Little equipment needed
- Doesn’t take up much space
Cons
- Needed a plasterer
- Didn’t give a thermal conductivity value
- Expensive
7: Steico Therm (wood fibre)
Steico therm are basically naturally sourced wood fibers that are compressed and made into slabs.
I was actually very close to purchasing this product also.
It was definitely a runner for many reasons.
- The Thermal conductivity was good
- It was not the most expensive in comparison to other insulations
- It was easy to apply
What changed my mind, in the end, was that it was missing one of the factors which were that we planned on using a stud wall to rest our ceiling on and this did not require a stud wall.
This was very similar to the hemp block but the only real difference was the thermal board was the Steico board had better thernal conductivity than the Hemp blocks.
Pros
- Good price
- Good Thermal Conductivity
- Easy to install
Cons
- Needs a plasterer to finish
8: Gutex (wood fibre)
This is basically the same as the Steico just the more premium brand.
Almost everything was exactly the same including the installation.
Pros
- Good Thermal Conductivity
- Easy to install
Cons
- Needs a plasterer to finish
- Bit more expensive than Steico
9: Calistherm board
This is a similar product to the timber Gutex and Steico boards but claims to be more intelligent, boasting mould prevention and moisture control.
It is made from a mixture of Lime and Sand and can absorb up to 4.7 times its own weight in water.
It is more expensive however than the timber boards.
The thermal conductivity was also higher but the thermal resistance was 0.85 m²K/W so it is a good all round insulator.
Pros
- Moisture control
- Easy to install
Cons
- Expensive
- Needs a plasterer to finish
10: Stud wall and dry line
This was something my engineer actually suggested.
I have heard it working on old stone houses before however it is a bit of a gamble as the insulation is not breathable.
How it works is you leave a gap of about an inch or two between the stud wall and the insulation board.
See the picture below for a clearer image.
We didn’t go for this for obvious reasons, 1 being we didn’t want to take the risk.
Our engineer told us that if you leave a gap for air to circulate then it would be ok and to be honest it definitely could work.
We actually removed something similar in a room on the west side of the house.
Lats of timber drilled into the wall, styrofoam placed in between the vertical lats and then plasterboard placed on top. We didn’t see any signs of dampness from it, which was amazing.
However we still didn’t want to take the chance
Pros
- Cheap
- Easy to install
- Doesn’t require lime plaster
Cons
- Not breathable insulation
- The price of insulated slabs or insulation boards are rising
11: Thermafleece CosyWool
This is essentially the same as Sheep’s wool just named something different by a different manufacturer.
75% of it is made from sheep’s wool while the rest is made from recycled fibers.
Pros
- Great thermal Performance
- Cheap
- Natural
- Easy to Install
- Quick to Install
Cons
- Lightweight
- Takes up internal space
Prices
These are the prices that I received based on 90m2.
All thicknesses vary but also as you can see so too do the prices.
The reason why the thicknesses vary is simply because some of the suppliers did not have a thicker product.
| Types | Thermal conductivity | Thickness | Price of 90m2 excluding Adhesive etc |
| Gutex Thermoroom | 0.039 W/mK | 60mm | €2,145 (ex VAT) |
| Calsitherm Climate Board | 0.059 W/mK | 50mm | €5,616 (ex VAT) |
| Steico Therm | 0.038 W/mK | 50mm | €1,289 (EX VAT) |
| Insulation Plaster | 50mm | €4,550 (EX VAT) | |
| Sheeps wool | 0.035 W/mK | 100mm | €2,358 (incl VAT) |
| Thermafleece CosyWool | 0.039 W/mK | 140mm | €1,278 (Ex VAT) |
| Hempcrete Block | 0.072 W/mK | 90mm | €3,173.9 (Ex VAT) |
| Hempcrete packing | 0.070 W/mK | 100mm | €2,227 (Ex VAT) |
| External Wrap | 0.037 to 0.040 W/mK | 100mm | €25,865 (EX VAT) |
| Thermo Hemp | 0.040 W/mK | 140mm | €1,921 (EX VAT) |
As you can see there are so many breathable insulations to choose from.
It really does depend on you.
What your budget can afford, what you would like to install and what suits you best.
The Hemp wool was best suited to us for a number of reasons but it might not be best suited to you.
Make sure to do your own research when purchasing insulation.
These prices were received in Ireland and they could be vastly different depending on what country you are in.
To help you along here is a link to a simple comparison table that I created.
You can input your findings in it yourself and compare them.
Just click the link below, go to file, make a copy and then save to your own Google drive.
You can edit it in your own Google Docs then.
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