Eco Friendly Insulation Materials Compared and What Works in Different Parts of a House

Sometime last year I finally sat down and started looking properly at how and where our house was losing heat. My first couple of attempts were half-hearted at best and centred around the classic mistake of attacking the places you can visibly see. New double glazing, new boiler, perhaps some draught excluders around the doors.

It took one of our energy assessors waving a thermal imaging camera at every wall in the house to make me realise I’d been looking at this completely the wrong way around. By far the worst areas of heat loss were neither visible nor tangible. They were buried deep inside the walls, under the floors, and above our heads in the roof.

Once I started learning about how and where to insulate, it became clear that effective insulation is about more than just stuffing the joists with wool. As well as understanding how heat loss occurs and where to stop it, you need to know what materials work best and where to use them. Choosing eco-friendly options can help to cut your heating bills down even further, massively reduce your carbon footprint and help the planet at the same time.

When done right, insulation can reduce home heat loss by up to 35 percent (Energy Saving Trust), dramatically reducing both your energy bills and carbon footprint. But when I started this journey I didn’t know the first thing about what materials to actually use, where to apply them or why some ‘eco-friendly’ options sounded amazing but actually make your problems worse. If you’re starting from zero too, here’s what you need to know.

After extensive research into eco-friendly insulation materials I’ve put together this complete guide covering:

• The different types of eco-friendly insulation materials
• The best places to install them in your house
• The most common DIY installation mistakes you should avoid

Lets start with a bit of science.

## All insulation materials are not equal…

It doesn’t matter if you go full“What John boy did last summer” absurdity and build an ‘igloo’ style insulated room in your loft. If you use the wrong materials it’ll just end up costing you more money to run your heating.

Thermal performance aside for a moment, sustainable insulation materials offer vastly different levels of embodied carbon. Better loft insulation materials such as natural fibre insulation can reduce embodied carbon by half when compared to mineral wool (Carbon Trust).

That’s great and all, but it doesn’t matter how sustainable your loft insulation material is if it doesn’t actually work.

Unfortunately, not all eco-friendly insulation options are suitable for every application. Installation location matters as much as the materials you use to do it.

I could’ve saved a fortune if someone had told me that at the start.

Natural materials such as sheep’s wool can absorb moisture from the air and release it again when conditions are drier, acting as a sort of built-in humidifier for your rooms. This is fantastic if you’re insulating solid walls on an older property as it literally allows your walls to breathe.

However, exactly the wrong thing to do if you install breathable insulation on half of your wall then cover it with an impermeable vapor barrier.

These materials can handle moisture better than traditional fiberglass options but trap it against the structure is a disaster waiting to happen.

Pretty much every natural insulation material I investigated has strengths in certain applications and huge drawbacks in others.

Eco material	Avg cost per m2	Typical application	DIY?	Overall Rating
Sheep’s wool	£8-£12	Loft insulation, timber frame walls	Yes
Cork Board	£15-£25	External Wall Insulation	No
Recycled Plastic / Denim / Newspaper	£5-£10	Vacant Homes / DIY Lofts	Yes

Time to dive into each of these materials to see where they work, and equally importantly, where they don’t.

## Sustainable Insulation Material Breakdown

Around a quarter of heat is lost through an uninsulated roof( Energy Saving Trust) so the loft should always be your priority. The best eco insulation material for your loft is going to depend on your specific use case. Are you going to be boardering it and creating a storage area or will you be using it to mount a ghetto trampoleneff.

### Sheep’s wool

I’ve heard a few people complain that wool insulation isn’t very fire resistant so it needs chemical fire retardants. This is complete nonsense. Sheep’s wool insulation does not need fire retardants. It’s naturally fire resistant.

In testing ( Gardiner Agency) wool insulation was exposed to direct flame point and began to char, not melt. Good old science.

So how does it stack up on actual heat loss? Its thermal performance is comparable to other natural options and better than many synthetics. Costs however are higher at around £8-12 per square metre compared to £3-5 per square metre for equivalent thickness of mineral wool.

### Cork Board

As you can guess from the name cork boards work amazingly well as loft insulation. Each tile is essentially a tiny bottle that’s had all the air squeezed out of it. What you’re left with has astonishingly good thermal performance and is completely natural.

It does have downsides though – cork is expensive. If you’re boarding your loft for storage then it works out fine but for straight insulation you’ll pay £15-25 per square metre compared to £6-8 for wool.

### Recycled Plastic, Denim and Newspaper

These all technically count as ‘natural’ insulation materials so I wanted to cover them, but honestly there’s not much natural about splitting water bottles to use them as insulation.

Recycled denim does have some benefits in very specific circumstances, mostly relating to its compression strength when installed inside timber frame walls. Most of these materials dont cope well with moisture so using them as loft insulation where ventilation is poor is a bad idea.

	Sheep’s Wool	Cork Board	Recycled Materials
Cost Per Square Metre	£8-12	£15-25	£5-10
Good For	Loft insulation, attics.	Lofts you’re boarding	Damp free lofts with excellent ventilation
Not Recommended For	N/A	Insulation where you cant add 20% thickness	Most homes.

Cavity wall insulation can reduce heat loss by up to 35 percent which is great but whether you can actually use it depends on the age of your property. The majority of cavity walls were built between 1920 and 1990 which accounted for two-thirds of all housing built( Dwelling). However, if you house was built pre-1920 you’re one of the 35 percent that have solid walls not cavities.

There are several options available for cavity wall insulation but due to the application method the only option available to you as a DIYer is blown insulation.

### Blown Wool

Just as it sounds wool insulation blown into the cavity. The compressibility of wool allows it to fill awkward spaces without settling like some other materials. It can also handle moisture better than most alternatives.

### Blown Cellulose

Cellulose insulation is usually made from recycled newspaper which is shredded and then blown into the cavity. Installation costs are high as this needs to be done by professionals but performance is excellent. The only downside to cellulose is that it does settle with time which will reduce thermal performance. Most manufacturers quote between 10-20% shrinkage which should be factored into your buying decision.

There are a huge number of external solid wall insulation options that require professional installation, some of which are environmentally friendly and some that arent.

A typical UK house contains around 45 tonnes of carbon ( The UN) so choosing lower embodied carbon materials can make a huge difference to the carbon footprint of your home.

Historic England recommend natural options wherever possible as external wall insulation typically accounts for approximately 45 percent of heat lost through an uninsulated solid wall home.

In my opinion cork has one of the best overall ratings when it comes to eco solid wall insulation. Installation is complex and will need to be done by a professional but it outperforms a lot of high-profile green alternatives.

One thing to consider with solid wall insulation materials is thickness. 100mm of PIR board will have better thermal performance than 100mm of wood fibre or sheep’s wool. Materials like cork need to be thicker to make up the difference.

Here’s how much thicker –

100mm PIR = 140mm Cork Board = 270mm Sheep’s Wool

Unfortunately this means that unless you’re fitting external solid wall insulation as part of a rebuild or new home you’re probably limited to either internal wall insulation or nothing at all.

We used cork board on our house because the game plan was to rebuild pretty much everything anyways so thicker material wasn’t a limitation.

	External Solid Wall Insulation
Material	Cork Board
Avg cost per m2	£100-£150
Remarks	27% thicker than synthetic options

Obviously if you can’t do external solid wall insulation due to budget or planning permissions your next best option is going to be internal.

Internal wall insulation isn’t something I’ve looked into personally so rather than guessing I’m going to point you towards the guys who have.

Homewith Granny have put together an excellent guide on internal solid wall insulation which covers both eco and traditional materials.

## Areas You Need to Insulate – Pros & Cons

No contest here. Your roof should always be your first priority for insulation as around a quarter of heat is lost through an uninsulated or poorly insulated roof ( UK Gov).

### Pros

Cutting heat loss through your roof will have instantly noticeable effects on the temperature in your home and the cost of your heating bills.

### Cons

There are no cons of loft insulation other than accessibility and physical effort if you’re doing it yourself. The higher up you can fit insulation the better.

Reducing the amount of heat you lose through your walls is the next most important area. Because of the installation process all of these options require professional installation.

### Pros

DIY cost is zero and increased thermal performance should be noticeable especially if your house is older with thin walls.

### Cons

Like loft insulation you won’t really notice performance decreases until its too late and you’ve already spent all your money. Caveat emptor.

Due to the nature of solid wall construction external insulation is always going to be more expensive than adding insulation to your loft or filling your cavities.

One of the biggest benefits to insulation is reducing heat loss through solid walls. Approximately 45 percent of heat is lost through solid walls in an uninsulated home( Historic England).

### Pros

As mentioned before external solid wall insulation is a game changer. If your able to make it work then do it.

### Cons

Not everybody can fit external wall insulation either due to planning restrictions of budget. Internal wall insulation is option #2 but will reduce the width of your rooms and doesnt apply to all properties.

Underfloor insulation is something a lot of people forget when they’re looking to reduce heat loss but it can account for up to 15% of heat lost( Energy Saving Trust).

### Pros

Again no chance to go wrong with underfloor insulation. Will instantly make your feet feel warmer.

### Cons

Depending on your floor type installing underfloor insulation can be a real pain and you might need professional help.

## Real Cost Comparison – How Much Will It Cost Me?

I created this chart to show you estimated costs for both DIY and professionally installed insulation materials. The assumption made with these figures is that installation cost for professionals will be £50 per hour and diy will take twice as long.

Costs will vary based on where you live in the UK but it should give you a ballpark idea for each specific insulation application.

Material	Diy	Professional install
Loft Insulation	Sheep’s wool insulation – £600-800 inc VAT	€1000-£1200 Inc VAT
Cavity Wall Insulation	N/A	€800-1200 Inc VAT
Solid wall external insulation	N/A	€8000-15000 Inc VAT
Underfloor	Sheep’s wool insulation – £400-700 inc VAT	€600-1000 Inc VAT

• 

• Thermal Imaging Survey – £200-£400. Know where to lose before you start spending money.
• Measure spaces – Grab a tape measurer and find out how much material you need. If you’re doing external solid wall insulation now is the time to get exact measurements.
• Planning (if necessary) – Assuming you don’t live in a standard brick box like mine’ll need to check for planning requirements. External wall insulation can require planning permission where other insulation materials do not.

• Loft Insulation – Allows you to save most money for the least effort. Focus on your loft first before lookelsewhere.
• If you have cavity walls professional cavity wall insulation – Done. Congratulations your hands are now free to enjoy a celebratory pint. Or summerroll.
• Solid wall insulation external – Will take a few months to organise and setup but will save you more money than pretty much anything else. Depending on where you live theres probably Grants available.

Insulating walls takes times,plan accordingly.

## Conclusion

In summary – insulate everywhere you can with sheep’s wool, its awesome.

Hopefully you’ve found this ultimate guide to eco-friendly home insulation helpful, if there’s anything I’ve missed that you’d love to know about get in touch.

Larry Leverage

Editor-In-Chief of MoneyZone and mediocre student of martial arts.